ABSTRACT CLEMONS, COURTNEY MOORE. Effects of Birth Characteristics, Nursing Behaviors, and Supplemental Milk on Piglet Pre-Weaning Growth and Survival

ABSTRACT CLEMONS, COURTNEY MOORE. Effects of Birth Characteristics, Nursing Behaviors, and Supplemental Milk on Piglet Pre-Weaning Growth and Survival. (Under the direction of Dr. William Flowers). The primary objective of this study was to determine the relative importance of various factors associated with the perinatal environment on pre-weaning survival and growth performance. Secondary objectives were to evaluate the effectiveness of administering an oral gavage of high-energy milk replacer within 24 hours after birth on subsequent pre-weaning survival and growth and to examine the compositional changes of colostrum over time in teats from different anatomical locations. Sixty-one sows were monitored during farrowing and length, timing, order, and other birth characteristics were recorded for 789 piglets. Body weights and nursing behaviors of piglets were recorded on days 1, 8, 15, and 22 of lactation. Piglets with similar birthweights that were nursing either the first two or last two pairs of teats were randomly assigned to receive nothing (control; n=205) or an oral gavage of 1 mL of milk replacer (n=204) between 12 and 24 hours after birth. Colostrum samples were collected from sows (n=8) between 1 and 4 hours prior to farrowing and again between 20 and 24 hours after the onset of farrowing from the first and last two pairs of teats. Colostrum concentrations of dry matter, protein, and IgG were higher in the anterior teats versus posterior teats (P < 0.0001) and decreased during the first 24 hours of lactation (P ≤ 0.001). Fat, IgA, and IgM concentrations all decreased (P ≤ 0.001) over time but were not affected by teat location (P ≥ 0.5059). Ash content was higher (P < 0.0001) in anterior than posterior teats and decreased over time only in posterior teats (P = 0.0249). Lactose content was higher (P < 0.0001) in anterior teats but did not change over time (P = 0.4268). Birthweight (P < 0.0001) and teat location nursed (P < 0.0001) were significant sources of variation for both growth and survival. Both decreased (P ≤ 0.05) as piglet birthweight decreased and as piglet nursing location became more posterior. Nursing

consistency was defined as the proportion of time piglets nursed the same nipple during lactation significantly affected piglet survival (P < 0.0001) with piglets having a nursing consistency of

99.6 + 0.1% having the lowest pre-weaning survival rates of 57.4 + 3.3%. Pre-weaning growth and weaning weights were greater (P < 0.05) for piglets without compared with their counterparts with umbilical hematomas at birth regardless of birthweight or the anatomical location of the teat nursed. Milk replacer did not affect piglet growth (P ≥ 0.2070) but improved survival (P ≤ 0.0429). Birth order, farrowing length, and birth interval (P ≥ 0.15) did not affect pre-weaning survival or growth performance. These results indicate that birthweight and the anatomical location of teats piglets nursed were significant aspects of the perinatal environment that affected their pre-weaning growth and survival; colostrum quality decreases significantly during the first 24 hours of lactation but to a greater extent in posterior than anterior teats; and an oral gavage of milk shortly after birth appears to have potential for improving pre-weaning survival.

Effects of Birth Characteristics, Nursing Behaviors, and Supplemental Milk on Piglet Pre- Weaning Growth and Survival

by Courtney Moore Clemons

A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science

Animal Science

Raleigh, North Carolina

2020

APPROVED BY:

______Dr. William Flowers Dr. Jonathan Holt Committee Chair

______Dr. Charlotte Farin Dr. Glen Almond

BIOGRAPHY Courtney Moore Clemons was born on February 17, 1996 in Gastonia, North Carolina to

Resa and David Moore. She has one older brother, Cory. Courtney graduated from Crest High

School in Shelby, North Carolina in 2014.

Courtney began attending North Carolina State University in August of 2014 and graduated with a Bachelor of Science degree in Animal Science with a minor in Leadership in

Agriculture and Life Sciences in May of 2018. She married her high school sweetheart, Justin

Clemons, in May 2018. In August 2018, she began pursuing a Master of Science in Animal

Science with a physiology concentration under the advisement of Dr. William L. Flowers at

North Carolina State University.

ACKNOWLEDGEMENTS I would like to thank Dr. William Flowers for his continual guidance throughout my graduate career. Dr. Flowers’s passion for swine reproduction and love for teaching makes him an exceptional mentor. Thank you for sharing your knowledge with me and inspiring me to continue in this field of research. I would also like to thank my committee members Dr.

Jonathan Holt, Dr. Charlotte Farin, and Dr. Glen Almond for their encouragement and insight.

I would like to thank Ivan Garcia for his support and willingness to help during each phase of my data collection at the Swine Educational Unit. Thank you for being so accommodating and supportive of my project. I would also like to thank my fellow graduate students for their encouragement and undergraduates Zoe Olmstead and Haley Cook for their tremendous help with data collection.

Lastly, I would like to thank my family and friends for their unwavering support. Thank you to my parents and grandparents for the love and encouragement you have given me every step of the way. A special thank you to my husband, Justin, for wholeheartedly believing in me and sharing this journey with me.

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TABLE OF CONTENTS LIST OF TABLES ...... v LIST OF FIGURES ...... vii Literature Review ...... 1 Introduction ...... 1 Porcine Mammary Gland Anatomy ...... 2 Mammary Gland Development and Function...... 3 Composition of Colostrum and Milk ...... 13 Piglet Nursing Behavior ...... 20 Piglet Pre-Weaning Mortality ...... 25 Conclusion ...... 37 Literature Cited ...... 38 Introduction ...... 45 Materials and Methods ...... 47 Animals, Facilities, and General Management ...... 47 Experimental Procedures ...... 48 Colostrum Composition Analyses ...... 50 Statistical Analyses ...... 51 Results ...... 54 Changes in Colostrum Composition ...... 54 Teat Selection by Piglets ...... 54 Piglet Pre-Weaning Survival ...... 55 Piglet Pre-Weaning Growth ...... 56 Discussion...... 59 Literature Cited ...... 67 Conclusions ...... 70 Tables ...... 72 Figures ...... 98 Appendices ...... 102 Appendix A. Descriptive Statistics ...... 103 Appendix B. Composition of Milk Replacer and Estimated Intake of Selected Nutrients ...... 104

LIST OF TABLES Table 1 Effect of Teat Location and Time Relative to Farrowing on Dry Matter (%) in Colostrum ...... 72 Table 2 Effect of Teat Location and Time Relative to Farrowing on Fat (%) in Colostrum ...... 73 Table 3 Effect of Teat Location and Time Relative to Farrowing on Protein (%) in Colostrum ...... 73 Table 4 Effect of Teat Location and Time Relative to Farrowing on Lactose (%) in Colostrum ...... 74 Table 5 Effect of Teat Location and Time Relative to Farrowing on Ash (%) in Colostrum ...... 74 Table 6 Effect of Teat Location and Time Relative to Farrowing on IgG Content (mg/mL) of Colostrum ...... 75 Table 7 Effect of Teat Location and Time Relative to Farrowing on IgA Content (mg/mL) of Colostrum ...... 76 Table 8 Effect of Teat Location and Time Relative to Farrowing on IgM Content (mg/mL) of Colostrum ...... 76 Table 9 Multiple Regression Analyses for First Pair of Teats Nursed by Piglets ...... 77 Table 10 Effect of Birthweight on Anatomical Location of Teats Nursed by Piglets during the First 24 Hours After Birth ...... 77 Table 11 Multiple Regression Analyses for Pair of Teats Nursed Most Often by Piglets ...... 78 Table 12 Main Effects of Selected Production Variables on Piglet Survival (%) During Lactation ...... 79 Table 13 Effect of Birthweight on Piglet Survival During Lactation ...... 80 Table 14 Effect of Anatomical Location of Teats Nursed During the First 24 Hours After Farrowing on Piglet Survival During Lactation ...... 81 Table 15 Effect of Anatomical Location of Teats Nursed During Lactation on Piglet Survival ...... 82 Table 16 Effect of Nursing Consistency on Piglet Survival During Lactation ...... 83 Table 17 Effect of Oral Gavage of Supplemental Milk During the First 24 Hours of Life on Piglet Survival During Lactation ...... 84 Table 18 Effect of Birth Interval on Piglet Survival During Lactation ...... 85 Table 19 Multiple Regression Analyses for Weight Gain (kg) During First Week of Lactation ...... 86

Table 20 Multiple Regression Analyses for Pre-Weaning Weight Gain (kg) ...... 87 Table 21 Multiple Regression Analyses for Weaning Weight (kg) ...... 88 Table 22 Effect of Birthweight on Piglet Pre-Weaning Growth Characteristics During Lactation ...... 89 Table 23 Effect of Anatomical Location of Teats Nursed During Lactation on Pre-Weaning Growth Characteristics of Piglets ...... 90 Table 24 Effect of Anatomical Location of Teats Nursed During the First 24 Hours After Farrowing on Pre-Weaning Growth Characteristics of Piglets During Lactation ...... 91 Table 25 Pre-Weaning Growth Characteristics of Piglets with Umbilical Hematomas at Farrowing ...... 92 Table 26 Effect of Providing Supplemental Milk During Lactation on Piglet Pre-Weaning Growth Characteristics ...... 92 Table 27 Effect of Sow Parity on Piglet Pre-Weaning Growth Characteristics During Lactation ...... 93 Table 28 Effect of Length of Parturition on Piglet Pre-Weaning Growth Characteristics During Lactation ...... 94 Table 29 Effect of Birth Interval on Piglet Pre-Weaning Growth Characteristics During Lactation ...... 95 Table 30 Effect of Nursing Consistency on Piglet Pre-Weaning Growth Characteristics During Lactation ...... 96 Table 31 Effect of Oral Gavage of Supplemental Milk during the First 24 Hours of Life on Piglet Pre-Weaning Growth Characteristics During Lactation ...... 97

LIST OF FIGURES Figure 1 Unique combination of colored zip-ties applied to piglets’ tails ...... 98 Figure 2 Piglet covered with meconium ...... 99 Figure 3 Normal umbilical cord (top) compared to umbilical cord with hematomas (bottom) ...... 99 Figure 4 Piglets nursing with different-colored crayon marks ...... 100 Figure 5 Summary of perinatal factors affecting piglet pre-weaning success ...... 101

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LITERATURE REVIEW Introduction

Improving prolificacy has been of major interest in swine production and has been primarily accomplished by increasing the total born piglets per litter. While genetic selection for total born piglets has been successful, it has prompted new challenges for pork production, with the main one being an increase in pre-weaning mortality. Pre-weaning mortality ranges from 16-

20% (Edwards and Baxter, 2015), which is considered high. For most genetic lines of sows, losses of 16-20% translates into approximately two piglets per litter, on average. These losses affect producers and present a major challenge for the pork industry. Thus, reducing pre-weaning mortality is of great importance for swine production.

Many factors influence piglet survival and growth and understanding these factors can provide means for reducing pre-weaning mortality. Access to nutrients during lactation for piglets is considered to be one of the most important of these factors. Proper mammary development and production of mammary secretions are critical for ensuring young piglets receive adequate nutrition to promote piglet survival and growth. Piglets must actively compete with their littermates for milk, and thus nursing behavior is of great importance during the pre- weaning period. While several factors such as birth weight, nursing behavior, and vitality are known to affect piglet growth and survival, there are still many that remain to be studied.

Consequently, the purpose of this literature review is to provide a brief summary of mammary gland anatomy and function in swine and then to concentrate on physiological, behavioral and environmental aspects of the postnatal period for the nursing piglet and their relationship with its growth and survival.

Porcine Mammary Gland Anatomy

The number of teats can vary considerably across sows, but typically falls between 12-18

(Martineau et al., 2012). From an anatomical perspective these should be arranged in 7 to 8 pairs spaced equally between the front and rear flanks to maximize milk production for piglets.

However, the U.S. industry standard is at least 12 functional teats, which is a more practical goal.

Teats are classified as anterior, middle, or posterior, depending on their location on the underline.

Teat location on the sow is very important, as poor teat location can hinder the piglets’ access to milk and result in piglet starvation and mortality (Martineau et al., 2012).

The mammary gland contains two types of tissue, parenchymal and extraparenchymal tissue. Parenchymal tissue is glandular and composed of the milk-synthesizing epithelial cells, or lactocytes. The extraparenchymal tissue is largely adipose tissue, commonly referred to as the fat pad. Mammary glands are distinctly separated from other adjacent glands. Each mammary gland is a complex gland, containing two simple glands which are independent ductal systems that exit the teat through separate teat canals. Simple glands are composed of tubuloalveolar tissue arranged in lobular alveoli, and lactocytes cover the interior surfaces of the alveoli. Once milk leaves the lobules, it enters the lactiferous duct and then flows through the teat canal to be ejected. In contrast to ruminants, mammary glands of the sow receive vascular supply through multiple arteries (Busk et al., 1999). The anterior mammary glands are supplied by the common carotid artery, and the posterior glands are supplied by a portion of the abdominal aorta (Farmer et al., 2007).

In prepubertal gilts, the mammary gland is largely composed of adipose tissue, or a fat pad, and only small amounts of parenchymal tissue are observed (Hurley, 2019). Mammary glands undergo drastic changes so that by the start of lactation, the mammary parenchyma has

2 exponentially increased in size and composes almost the entire mammary gland. Unlike other livestock species, the mammary gland of the sow lacks teat cisternae, which prevents much storage of milk. Because of this limited storage capacity, the mammary gland reaches capacity relatively quickly and must be emptied approximately every 50-70 minutes by the nursing piglets

(Farmer et al., 2001).

Mammary Gland Development and Function

Mammary tissue develops from the ectoderm layer of the embryo. At birth, porcine mammary glands are poorly developed and mainly composed of subcutaneous stromal tissue

(Martineau et al., 2012). Most of mammary development occurs rapidly in three distinct phases:

90 days of age until puberty, the last third of gestation, and throughout lactation. Little mammary growth occurs before day 90 of age. Before the first phase of rapid development, the mammary gland is mostly extraparenchymal tissue with very little parenchymal tissue. Accretion of mammary tissue accompanied by an increase in mammary DNA occurs between day 90 and puberty (Sorensen et al., 2002). Puberty has been observed to aid in mammary development by stimulating a 51% increase in parenchymal tissue and a 16% decrease in adipose tissue (Farmer et al., 2004). Estrogens play an essential role for triggering the onset of puberty and thus the pubertal alterations of mammary tissue. The result of the first stage of rapid development is that by the time of mating, mammary glands remain relatively small but now contain an extensive duct system (Farmer and Hurley, 2015).

The second stage of rapid mammary development occurs during the last third of gestation, which marks exponential growth of the mammary gland. Not only does the mammary tissue drastically increase in tissue mass and DNA, but histological and compositional changes also occur. Prior to this stage adipose tissue comprises the majority of the mammary gland;

3 however, after day 75 of gestation, lobuloalveolar tissue largely replaces the extraparenchymal tissue. By day 110 of gestation, the mammary gland is now mostly comprised of parenchymal tissue (Farmer and Hurley, 2015). Elevated estrogen and progesterone concentrations in maternal circulation stimulate these changes via local modulation of growth factors (Ash and

Heap, 1975). Furthermore, the composition of mammary tissue drastically shifts from high lipid to high protein. Lastly, differentiation of the epithelial cells comprising the secretory tissue occurs between days 90-105 of gestation, indicating the onset of the lactogenic process. The growth of each mammary gland during gestation is influenced by its location on the underline.

By the end of gestation, the middle glands (third, fourth, and fifth pairs) grow to be largest, while the posterior glands (sixth, seventh, and eighth pairs) remain smallest in size (Farmer and

Hurley, 2015).

The last stage of rapid mammary development occurs during lactation. At this time, glandular parenchyma largely replaces connective tissue (Farmer and Hurley, 2015). The resulting mammary gland is composed of tubuloalveolar tissue consisting of secretory lobules lined by lactocytes. Between days 5 and 21 of lactation, the average weight of the mammary gland increases by 57%. Both hyperplasia and hypertrophy contribute to this increase for first- parity sows, but hypertrophy is primarily responsible for the weight increase in multiparous sows

(Farmer and Hurley, 2015). As with gestation, mammary growth during lactation is largely dependent on anatomical location of the glands. The smallest glands experience the most growth while the largest glands have the least amount of growth. Specifically, gland pairs 1, 6, 7, and 8 increase in mass by day 5 of lactation, while glands 2 and 3 experience very little growth.

Interestingly, the largest middle glands do not grow at all, but regress by day five of lactation

(Hurley, 2019). Milking capacity is directly related to the amount of lactocytes in each

4 mammary gland, which is reflected by the size of the mammary gland (Martineau et al., 2012).

Thus, the largest glands during lactation are capable of producing the most milk, while the smallest glands yield the least amount of milk. This is also affected by suckling intensity, which will be discussed subsequently.

Mammogenesis is largely under hormonal control. As previously mentioned, estrogens are essential for stimulating pubertal developmental changes. Additionally, estrogens and relaxin synergistically stimulate parenchymal tissue development (Farmer and Hurley, 2015).

Relaxin, produced by the corpora lutea, actively increases parenchymal tissue and decreases adipose tissue during the last third of gestation. Development of lobuloalveolar tissue during gestation is prompted by elevated estrogen and progesterone concentrations in maternal circulation (Ash and Heap, 1975). While prolactin is largely attributed for its role in lactation, the anterior pituitary peptide hormone is also active between days 90-109 of gestation, eliciting parenchymal tissue growth (Farmer and Hurley, 2015). Concentrations of growth hormone in maternal circulation remain stable throughout gestation and studies of the administration of exogenous growth hormone have varied results (Farmer and Hurley, 2015). However, it has recently been reported that exogenous porcine somatotropin (pST) can stimulate mammary development of parenchymal tissue during days 90-109 of gestation in gilts, likely through a 4- fold increase in insulin-like growth factor-1 (IGF-1) (Farmer and Langendijk, 2019).

Lactogenesis

Lactogenesis refers to the ability of the mammary tissue to synthesize and secrete milk and can be described by two phases. During the first phase of lactogenesis, the mammary tissue is being prepared to synthesize milk components (Hartmann et al., 1995). Milk components

5 begin to appear in the alveoli between days 90 and 105 of gestation, and there is scant secretion of milk during this phase of lactogenesis. Phase II of lactogenesis marks the beginning of milk synthesis and secretion (Hartmann et al., 1995), and the prepartum surge of prolactin prompts the transition from phase I to phase II of lactogenesis (Martineau et al., 2012; Quesnel et al., 2015).

A decline in circulating progesterone concentrations at farrowing (via lysis of the corpora lutea) triggers the prepartum rise in prolactin concentrations, thus initiating milk synthesis.

Importantly, onset of milk production is inhibited without the prepartum rise in prolactin

(Quesnel et al., 2015).

Lactation begins around the time of parturition and can be categorized both by the type of mammary secretions produced and the phase of milk production. The initial mammary secretion is colostrum, which is primarily synthesized before parturition and ingested by the piglets for the first 24 hours after the onset of parturition. Colostrum is notably rich in immunoglobulins and contains less lactose and lipids than later mammary secretions. After this time, mammary secretions begin to change in composition and are termed transient milk until day 4 of lactation.

Lastly, mature milk refers to the mammary secretions produced from day 10 of lactation until weaning, and remains relatively stable in composition (Quesnel et al., 2015).

Milk production in the sow can be described by four phases. The first phase, or colostral phase, occurs during the first 24-48 hours after parturition and coincides with secretory differentiation. During this phase, colostrum is secreted by the mammary glands, but only slight growth of piglets is observed (Kim et al., 2000). Adequate colostrum intake is critical for newborn piglets, as colostrum contains high concentrations of immunoglobulins that supply the neonatal piglets with passive immunity. Unlike the subsequent phases of milk production, colostrum is continuously available for the nursing piglets to suckle. After the colostral phase,

6 mammary secretions become cyclical and milk is only available for the nursing piglets during specific time periods. Additionally, the subsequent phases of lactation coincide with secretory activation, during which time mammary secretions allow for linear growth of the nursing piglets

(Kim et al., 2000).

The second phase of milk production, referred to as the ascending phase, occurs as colostrum transitions to milk approximately 24 hours after onset of parturition. The transition of colostrum to milk is primarily marked by a decline in immunoglobulin concentrations. During the ascending phase, both nursing frequency and quantity of milk at each nursing increase

(Martineau et al., 2012). Also, during this phase, it is believed that the nursing order, or the teats that piglets nurse through the remainder of lactation, is established. This phenomenon will be further discussed in a subsequent section. If any teats are not nursed during the first 36 hours after parturition, those teats will begin to involute and become nonfunctional for the remainder of that lactation (Theil et al., 2006).

The third phase of milk production, or the plateau phase, begins after day 10 of lactation.

During this phase, milk production can be adjusted based on suckling intensity, but becomes insufficient to allow for maximal piglet growth. This is especially evident in large litters

(Martineau et al., 2012). In fact, it has been observed that the growth limitation for piglets during later stages of lactation can be as much as 2 kg per piglet due to inadequate milk supply

(Harrell et al., 1993). The issues associated with inadequate milk supply probably have only increased in the recent years due to selection pressures for increasing litter sizes.

Piglets raised in commercial settings may or may not experience the last phase of milk production, or the descending phase. When weaning is done at approximately 21 days, pigs are weaned at the peak of lactation and do not experience the descending phase. However, lactations

7 lasting greater than 21 days will enter this phase. If nursing proceeds without any intervention, the descending phase will continue until involution occurs at approximately 6-8 weeks.

Milk Removal and Ejection

Milk ejection in the sow varies depending on the stage of lactation. During the colostral phase of lactation, mammary secretions are spontaneous and almost continually available for piglets to suckle due to very high concentrations of oxytocin. After the colostral phase, milk ejection becomes strictly cyclical and requires teat stimulation from the piglets. The pre-ejection teat massage triggers removal of milk from the alveolar ductal system via the neuroendocrine milk ejection reflex (Fraser 1980). Described briefly, tactile stimulation from the piglets prompts the release of oxytocin, which then causes the myoepithelial cells surrounding the alveolar lumen to contract. This contraction results in milk being forced through the ductal system and into individual teats to be ejected. The entire process of milk ejection occurs quite quickly. A 1-3-minute interval of teat stimulation prompts oxytocin release and within approximately 30 seconds milk is ejected (Ellendorff et al., 1982), resulting in a brief 10-20 second interval of milk release (Fraser, 1980).

Milk ejection is also regulated by accumulation of autocrine feedback inhibitory factor(s)

(Farmer and Hurley, 2015). As milk gathers in the mammary glands, autocrine feedback inhibitory factor(s) build up in the mammary alveoli, preventing further cellular secretion of milk components until the gland is suckled. Once the mammary gland has been fully emptied, the inhibitory control is removed, and oxytocin is released to prompt further milk secretion.

Furthermore, suckling stimulates prolactin secretion. Prolactin secretion and removal of the feedback inhibitory factor have synergistic control on the mammary gland to maintain lactational function and prompt mammary growth (Farmer and Hurley, 2015). Build-up of the autocrine

8 feedback inhibitor limits further milk secretion and if not removed will trigger mammary involution.

Mammary Involution

Mammary gland involution describes the regression of mammary tissue after cessation of nursing, which reverts the glandular morphology back to that of a non-pregnant state. Weaning primarily causes mammary gland involution due to an abrupt cessation of milk removal. Post- weaning mammary involution is mostly complete within 7 days and can be divided into three phases (Ford et al., 2003). The first phase of involution, days 0-2 post-weaning, marks the most drastic regression of mammary tissue. The lack of milk removal from weaning causes milk stasis in the mammary gland, which initially causes the mammary glands to swell on day 1 post- weaning until reabsorption of milk in the lumen occurs. Accumulation of autocrine feedback inhibitor of lactation in the lumen of alveolar cells prevents further milk secretion. By post- weaning day 2, the cross-sectional area, glandular weight, and parenchymal DNA have all significantly decreased. Alterations in mammary tissue observed in the subsequent two phases, days 2-4/5 and days 4/5-7 post-weaning, respectively, are minor compared to what occurs in the first phase of involution. Secretory mammary tissue and parenchymal DNA continue to decrease so that by day 7 post-weaning, a 69% reduction in parenchymal tissue wet weight and a 67% decrease in parenchymal DNA is observed (Ford et al., 2003). The rapid regression of parenchymal tissue causes a significant reduction in protein percentage and increased fat percentage of the mammary tissue (Farmer and Hurley, 2015). Although this pattern of involution is fairly consistent for litters weaned at three weeks of age, mammary involution may initiate before complete weaning for lengthier lactations, as observed by Farmer et al. (2007).

Mammary involution can also occur in early lactation, and mammary glands that remain unsuckled by day 3 of lactation will regress. Involution at the beginning of lactation follows a similar pattern as involution that occurs after weaning, with a 67% reduction in wet weight mammary tissue by the first 7-10 days of lactation (Ford et al., 2003). Importantly, mammary glands that regress in early lactation do not undergo any further loss of mammary parenchymal tissue at weaning. Regression of unsuckled glands is reversible within the first 24 hours of lactation but is permanent by day 3 of lactation (Theil et al., 2005). However, glands that are unsuckled initially but then are nursed have lower milk yield throughout lactation compared to regularly suckled glands. It is imperative that mammary glands are suckled for the first 36 hours postpartum to prevent early involution. This critical window of time is explained by the transition into the secretory activation phase of lactogenesis (Theil et al., 2014), when milk replaces colostrum secretions at approximately 34 hours.

Role of Mammary Secretions and Factors Influencing Their Production

As mammary secretions are the primary source of nutrients for neonatal piglets, adequate intake of colostrum and milk during lactation is vital for piglet growth and survivability. Ample yield of colostrum and milk combined with successful piglet consumption is critical for combatting pre-weaning mortality. Colostrum is essential for early postnatal survival because it serves as the initial source of energy and passive immunity for the piglet. Piglets are born without thermogenic brown adipose tissue and with very little lipid content. Their main sources of heat-production are hepatic and muscle glycogen, which will be completed expended by 12-17 hours postnatal without consumption of colostrum (Quesnel et al., 2015). In addition to a lack of thermoregulatory ability, piglets are also born without immunoglobulins and functional immune cells, which are necessary for proper immune function. Only through consumption of colostrum

10 can piglets obtain the required immune cells to fight off pathogens. Thus, without timely ingestion of colostrum, the chances of piglet survival greatly diminish.

Consumption of transient and mature milk is a major determinant of piglet growth rate

(Quesnel et al., 2015). Once the mammary secretions transition from colostrum into milk, the sow cannot produce enough to meet the piglets’ demands. Thus, sow milk yield is a limiting factor for piglet growth (Harrell et al., 1993), a fact that has only been exacerbated by the increased emphasis placed on hyperprolific sow lines. Adequate milk consumption not only benefits piglet growth during the pre-weaning period but is also advantageous for post-weaning performance; as a linear relationship exists between weaning weight and average daily gain

(ADG) during the nursey phase of production (Cabrera et al., 2010).

Total colostrum yield is highly variable between sows, and unlike milk production, is not strongly influenced by litter size and weight. Factors that impact colostrum yield include sow parity and endocrine status (Quesnel et al., 2015). Parity 4 sows and older have been shown to produce less colostrum than younger parity sows. Lactogenesis relies on hormonal control of progesterone and prolactin. The prepartum peak in prolactin, stimulated by decreased progesterone concentrations, is critical for causing lactogenesis (Quesnel et al., 2015).

Alterations in these hormone profiles can have impacts on colostrum production in the sow. It has been observed that primiparous sows can experience delayed declines in progesterone concentrations, which delays the prepartum peak of prolactin. This occurrence has been seen to significantly reduce the total yield of colostrum (Foisnet et al., 2010). It is speculated that mammary gland development, sow metabolic status, and gestational nutrition may also play a part in impacting colostrum yield, however more research is still needed in these areas (Quesnel et al., 2015).

The number of suckling piglets is a major determinant of milk yield in the sow, and milk production increases as both litter size and birth weights increase (Martineau et al., 2012;

Quesnel et al., 2015). Larger piglets remove more milk from mammary glands, thus allowing for greater refilling. Conversely, smaller piglets remove less milk, which restricts subsequent milk secretion. Furthermore, glands suckled by larger piglets grow significantly larger during lactation than glands nursed by smaller piglets (Kim et al., 2000), meaning more lactocytes are present for greater milk yield. Although milk production increases as litter size increases, the amount of milk ingested per pig significantly decreases. Auldist et al. (1998) reported that when litter size increases from 6 to 14 pigs nursing, milk ingested per piglet decreases from 1.63 to 1.11 kg/day.

Thus, milk production remains a limiting factor of piglet growth even with larger litters.

Additional factors impacting milk production include genetics, parity, litter size and behavior, environment and management, nutrition, and endocrine status. Between the 1970s and late 1990s, milk yield increased due to genetic selection, but has remained constant since.

Selecting for number of functional teats has recently been studied as a means for further improving milk yield of the sow (Lundeheim et al., 2012). It is evident that breed influences milk yield, which is illustrated by Chinese-derived sows producing more milk than typical European breeds (i.e. Landrace, Large White), and European breeds producing more than meat breeds (i.e.

Duroc, Pietrain) (Quesnel et al., 2015). A sow’s parity also affects milk yield, with maximum production observed for parities 2-4 (Dourmad et al., 2012). The environment for lactation can alter milk production negatively if continuous loud noises are present or if staff is often disturbing the lactating sows and their litters. Loud noises that startle the piglets can cause the piglets to perform less teat stimulation, resulting in less milk secretion. Disruptions from staff can cause early termination of nursing bouts, ultimately decreasing milk output. Heat stress is

12 another issue that impacts milk yield, as high temperatures from 27 to 32°C decrease sow milk yield (Farmer and Prunier, 2002). The importance of nutrition for milk production is typically only seen with severe restriction; it is suspected that sows may compensate for less severe nutritional deficiencies by mobilizing their own body tissues to support lactation (King and

Dunkin, 1986).

Composition of Colostrum and Milk

The composition of colostrum and milk is most notably influenced by stage of lactation.

Both milk and colostrum contain various nutrients and bioactive factors necessary for piglet growth and survival. As discussed above, colostrum is rich in energy and immunoglobulins, which are crucial for immune development and survival of neonatal piglets. Colostrum also contains higher amounts of various microminerals, vitamins, hormones, and growth factors relative to milk, but contains lower concentrations of lactose (see review by Hurley, 2015).

While transient milk contains elevated fat concentrations, the lipid composition of mature milk remains fairly stable throughout lactation. Although mammary secretions undergo many changes as colostrum transitions to milk, the composition of mature milk after day 7-10 postpartum remains mostly unchanged throughout the remainder of lactation.

The major components of colostrum and milk for a 3-week lactation can be categorized by class of nutrients, as discussed in the following sections. It should be noted that water is a critical component of colostrum. Water accounts for 73% of mammary secretions, on average, during and immediately following parturition and remains relatively stable for the duration of lactation at 77-81% (Hurley, 2015). Not only is water the primary liquid component of milk but it is also an essential nutrient.

Carbohydrates

Lactose is the main carbohydrate present in mammary secretions and has the least variation throughout lactation. Concentrations of lactose are relatively low in colostrum and gradually increase as colostrum is replaced by transient milk. Lactose concentrations remain relatively stable in mature milk, accounting for approximately 5.2% of total solids, on average

(Hurley, 2015). Additional carbohydrates present in mammary secretions include glucose and galactose, although their concentrations are low compared to lactose. Both glucose and galactose are highest in early lactation with a peak in glucose at day 3 of lactation and galactose concentrations highest in colostrum (Atwood and Hartmann, 1992). Several complex carbohydrates contribute to the carbohydrate portion of mammary secretions, with oligosaccharides having highest concentrations in colostrum (Tao et al., 2010).

Lipids

Lipid concentration is the most variable component of sow mammary secretions. On average, lipid accounts for 5.9-6.4% of total solids, transiently peaks between 24 hours and day 3 postpartum, then holds steady at 7.0-7.6% for the remainder of lactation (Hurley, 2015). The peak in lipid content coincides with the transient phase of milk production as colostrum is transitioning into mature milk.

Protein

The protein component of mammary secretions is comprised of protein bound amino acids, major milk proteins, casein and whey protein, immunoglobulins, and non-protein nitrogen

(NPN). Concentrations of total protein are highest at parturition, accounting for an average of

16.6% of total solids, and remain elevated through the first 4 hours postpartum (Hurley, 2015).

These heightened levels of protein during early lactation are namely due to the highly prevalent immunoglobulins in colostrum. Indeed, both immunoglobulin concentration and total protein concentration decrease by over 50% by 24 hours postpartum (Hurley, 2015). Total protein concentration continues declining through the transient milk phase and remains between 5-5.4% of total solids in mature milk.

Glutamate and proline are the most prevalent protein bound amino acids in mammary secretions, while casein and whey protein are the major milk proteins in mammary secretions.

Casein concentrations vary inversely with immunoglobulin concentrations. Thus, casein increases over the first 24 hours postpartum as immunoglobulins decline (Brent et al., 1973;

Csapo et al., 1996). Once mature milk is being secreted, casein comprises 50-55% of total protein, on average (Hurley, 2015). At parturition, whey protein accounts for an average of 90% of total protein, with immunoglobulins as the primary components. Whey protein declines during the colostral phase, reaching approximately 70% of total protein by 24 hours postpartum

(Hurley, 2015), and accounts for 47-50% of total protein in mature milk (Csapo et al., 1996).

Once immunoglobulins have declined after the colostral period, β-lactoglobulin becomes the major whey protein in mammary secretions. Non-protein nitrogen includes free amino acids, nucleotides, and amino sugars. Non-protein nitrogen concentrations are lowest in colostrum and increase throughout lactation.

Immunoglobulins are the main protein components in colostrum. Specifically, immunoglobulin isotypes IgG, IgA, and IgM are found in colostrum (Hurley, 2015).

Concentrations of all three isotypes are highest at parturition and remain elevated for several hours postpartum, with IgG being most prevalent. IgG concentrations decline rapidly during the first day of lactation, with an almost 50% decline by 12 hours postpartum. Following the

15 colostral phase, IgG concentrations remain low for the remainder of lactation. Likewise, IgM and IgA decline significantly during the first day of lactation, but their decline is more stable compared to IgG.

Minerals

Several minerals and microminerals have been characterized in mammary secretions.

Calcium and phosphate concentrations increase as colostrum transitions into mature milk, however diffusible calcium concentrations are highest in colostrum (Hurley, 2015). Conversely, sodium, potassium, chlorine, and sulfur are present in greater concentrations in colostrum than milk. Most milk components are synthesized in a high potassium low sodium environment within the mammary epithelial cells, and the composition of mammary secretions reflects this association. Most notable of the microminerals, copper, iron, iodine, manganese, selenium, and zinc are all more prevalent in colostrum than mature milk.

Vitamins

Vitamins A, E, and C concentrations are typically higher in colostrum than mature milk.

On average, vitamin C is highest at 190 and 94 ug/ml; followed by vitamin E at 10 and 2.6 ug/ml; and vitamin A at 1.14 and 0.48 ug/ml, for colostrum and milk, respectively. Much variability has been reported with vitamin E concentrations, and vitamin K does not appear to be affected by stage of lactation. Although research is limited for B vitamin concentrations in mammary secretions, riboflavin, niacin, and folic acid seem to follow similar patterns as those observed for vitamins A, E, and C (Hurley, 2015).

Cells

Somatic cells of mammary secretions include neutrophils, macrophages, lymphocytes, eosinophils, and epithelial cells. Much variation has been reported when characterizing total somatic cell counts, and this variation likely results from subclinical mastitis, route of oxytocin for milk sampling, or teats collected from, which were not accounted for in initial collections

(Hurley, 2015). Neutrophils comprise most of the cellular portion of mammary secretions, averaging 69.4% of total cells in colostrum and 47.9% of total cells in milk (Hurley, 2015). The next largest cellular components are lymphocytes and macrophages, while eosinophils total to less than 2% of total cells in mammary secretions. As lactation progresses, neutrophils decrease in concentration, lymphocytes and macrophages remain relatively stable, and epithelial cells drastically increase. Alterations in the cellular component of milk continue so that at weaning,

90-98% of cellular milk components are neutrophils (Hurley, 2015).

Energy

Changes in gross energy of mammary secretions are associated with variations in both immunoglobulins and lipids during early lactation. Colostral secretions contain elevated gross energy, and these levels continue through at least day 3 of lactation. Gross energy declines after approximately day 3 of lactation. Highly prevalent immunoglobulins contribute to the increased gross energy in colostrum, while the peak in fat content is likely responsible for keeping gross energy elevated through approximately day 3 of lactation (Hurley, 2015).

Bioactive Factors

Mammary secretions of the sow contain many diverse biologically active components, including immunoglobulins, leukocytes, enzymes, hormones, and growth factors. Importantly,

17 many of the hormones, growth factors, and cytokines are hypothesized to influence the neonate.

Hormones present in mammary secretions include prolactin, relaxin, estrogens, progesterone, cortisol, and thyroid hormones (Hurley, 2015). Prolactin concentrations are influenced both by the stage of lactation and litter size. Prolactin is most elevated just prior to parturition; rapidly declines during the first day of lactation (Devillers et al., 2004a); and transitions to a gradual decrease for the remainder of lactation. Larger litters of 10-12 nursing piglets have higher prolactin concentrations in mammary secretions compared to smaller litters of 8 piglets.

Furthermore, a positive correlation between serum and milk prolactin is observed through at least day 13 of lactation (Hurley, 2015). Concentrations of estrogens, progesterone, cortisol, insulin, and neurotensin are all higher in colostrum compared to subsequent stages of lactation (Devillers et al., 2004a; Hurley, 2015), while thyroid hormones remain largely unchanged during lactation.

Insulin-like growth factor-1 concentrations are highest in colostrum; followed by a rapid decline during day 2 of lactation; and a gradual decrease until day 10 of lactation (Monaco et al., 2005).

Additionally, several cytokines have been characterized in mammary secretions, each of which are highest in early lactation and decline throughout lactation (Hurley, 2015).

Lastly, the pro-form of relaxin is found in mammary secretions, with highest concentrations observed in colostrum (Yan et al., 2006). Interestingly, relaxin appears to be important for maternal programming of neonatal development, as described by the lactocrine hypothesis (Bagnell and Bartol, 2019). The lactocrine hypothesis describes how milk-borne bioactive factors (MbFs) delivered from mother to young during nursing can affect the trajectory of offspring development (Bagnell et al., 2017). Reproductive tract development completes postnatally (Bartol et al., 1993), creating a window of opportunity for maternal lactocrine programming. It has been reported that MbFs in colostrum significantly impact the development

18 of female uterine and cervical tissues and lack of colostrum consumption can have long-term consequences on prolificacy and fecundity by impairing uterine capacity (Bagnell and Bartol,

2019). Relaxin has been proposed as a prototypical lactocrine-active factor important for maternal programming of female reproductive tissues. Bioactive relaxin is present in colostrum, only detectable in neonatal circulation if piglets nurse colostrum, and has been shown to have trophic effects on neonatal cervical and uterine tissues (Bagnell and Bartol, 2019).

Variation in Colostrum and Milk Composition Among Teats

Recent studies have analyzed differences in colostrum and milk composition among teats at different anatomical location. Colostrum has been observed to vary greatest in protein, dry matter, and total IgG concentrations between anterior and posterior teats. Anterior teats have been shown to contain significantly higher concentrations of these nutrients than posterior teats, with a gradual decrease for more posterior teats (Lannom, 2018). Likewise, dry matter and fat concentrations of milk were reported as significantly greater in anterior teats compared to posterior teats (Lannom, 2018; Farmer et al., 2015). Conversely, lactose concentrations in milk were reduced in the third pair of teats compared to all other locations (Lannom, 2018). These differences may be due to mammary development, blood flow, or suckling frequencies. As previously discussed, the amount of mammary growth differs depending on the anatomical location, and different vasculature supplies anterior and posterior glands. In addition, larger piglets prompt greater milk yield through increased suckling intensity. Any of these factors may contribute to the variation seen among teat location; however, more research is needed to conclusively state any effects.

Piglet Nursing Behavior

Nursing Behavior Related to Stage of Lactation

Nursing behavior during the colostral period of lactation differs from the nursing behavior during later stages of lactation. During parturition, colostrum is almost continually available for piglets to suckle, and teat stimulation is not required for milk ejection. Within hours after birth, piglets navigate to the udder and begin sampling various teats (de Passillé and

Rushen, 1989), without any preference for teat location. This teat sampling behavior continues for the first 8 hours postpartum (de Passillé et al., 1988), during which time it is advantageous to suckle from more teats to increase colostrum consumption. Individual piglets fall into cycles of

2-3 hours of activity, followed by rest periods, which gradually transform to synchronized nursing bouts within the first 12 hours postnatally (de Passillé and Rushen, 1989). These early nursing bouts typically only involve a few piglets at a time, with small groups of piglets following separate suckling rhythms. By 10 hours postpartum, colostrum is no longer continually available, but is ejected cyclically at a constant rate of 1.5 times per hour.

Furthermore, by 12-16 hours postpartum, colostrum ejection is no longer spontaneous, but must be stimulated by teat massaging from piglets’ snouts (Špinka and Illmann, 2015). Only approximately 85% of the litter participates in nursing bouts by day 1, with complete nursing synchronization not occurring until day 3 postpartum (de Passillé and Rushen, 1989).

The transition from the colostral period of lactation to established lactation is not only marked by the change in milk that is excreted from the mammary glands, but also by a substantial shift in nursing behavior. By as early as 10 hours postpartum, piglets are beginning to nurse in cyclical nursing bouts, and complete suckling synchronization occurs at day 3 postpartum (de Passillé and Rushen, 1989). This progression is both a behavioral and

20 physiological one. During early postpartum, oxytocin concentrations are markedly high, allowing for spontaneous milk excretion (Quesnel et al., 2015; Špinka and Illmann, 2015).

Oxytocin concentrations then decline as cyclical sucklings begin to develop and milk excretion starts to be dependent on teat stimulation from the piglets that triggers pulsatile oxytocin secretions. The cyclical nursing bouts become more distinct as more of the litter participates, and complete synchronization or established nursing is marked by the entire litter nursing at defined intervals.

As lactation continues, the amount and duration of nursing episodes begins to shift.

While a slight increase in nursing frequency is observed between the first 24 hours postpartum and second week of lactation, both frequency and duration decline thereafter until weaning. The sow is primarily responsible for this decline. At the beginning of lactation, the sow initiates 80-

100% of nursing episodes, but by week 4 that percentage drops to less than 10% (Špinka and

Illmann, 2015). If piglets are left to naturally wean, the nursing frequency will continue to decline until piglets are completely weaned at 6-8 weeks of age (Špinka and Illmann, 2015).

During the established nursing phase of lactation, distinct nursing bouts occur fairly consistently with one nursing every 50 minutes. Each complete nursing episode lasts for several minutes and consists of five main phases. The first phase, nursing initiation, can be triggered by the sow or the piglets. The sow can initiate by lying laterally, exposing the underline, and emitting rhythmic nursing grunts to attract the piglets. Conversely, the piglets can initiate by individually approaching the sow, vocalizing near the sow’s mouth and massaging her underline with their snouts. This behavior will continue until enough piglets join to stimulate the sow to expose her underline and begin rhythmically grunting. After this occurs, the second phase, pre- ejection teat massage, begins. During this phase, the piglets intensely massage and occasionally

21 suckle their respective teats. The tactile stimulation from the piglets continues for 1-3 minutes until enough stimulation triggers a surge of oxytocin for milk ejection (Ellendorff et al., 1982).

Milk ejection, the third phase of a nursing episode, is the shortest phase and only lasts for 20 seconds on average. During milk ejection, milk is released synchronously from all mammary glands. Milk ejection can be observed by watching the litter’s behavior. Once milk is released, piglets stop massaging the teats with their snouts and begin firmly holding the teats and distinctly suckling. The ejection phase can also be observed by the sow’s vocalizations. Before milk ejection, the sow grunts approximately every two seconds, but during milk ejection, grunts rapidly increase to about two grunts per second. Once milk ejection has completed, the frequency of grunts decreases again, and there is a refractory period of approximately 20 minutes wherein no amount of teat massaging can stimulate milk release. The fourth phase, or post- ejection teat massage, occurs once milk ejection has ceased. Piglets then switch back to massaging their respective teats instead of suckling them. Although the post-ejection teat massage may last for several minutes, the time and number of piglets contributing is highly variable. As lactation progresses and the sow begins terminating more of the nursing episodes, post-ejection teat massaging becomes more limited. The final phase of a nursing episode is nursing termination. Termination can be triggered by either the piglets falling asleep at or leaving the underline or by the sow rolling over or standing to no longer expose the udder. The predominant nursing behavior during each nursing episode is teat massaging. Teat massaging is required for milk ejection, which marks the importance of this behavior. The pre-ejection teat massage is most critical, as it takes between 1-2 minutes for the piglets’ tactile stimulation to trigger milk ejection. Post-ejection teat massage is much more equivocal but thought to be associated with inadequate milk consumption (Špinka and Illmann, 2015).

Interestingly, not all nursing episodes result in milk ejection. Non-nutritive nursings follow a similar initiation as nutritive nursings, but tactile stimulation from the piglets fails to stimulate a surge of oxytocin and subsequent milk ejection. Non-nutritive nursings can be identified by noting the sow’s vocalizations and piglet’s nursing behavior during what should be the milk ejection phase. The sow does not exhibit a peak in grunting and piglets do not display distinct suckling motions with the absence of milk ejection. Non-nutritive nursings can constitute 5-30% of total nursing episodes throughout lactation and have been suggested to be a physiological strategy to down-regulate milk output when piglets initiate nursings too frequently

(Špinka and Illmann, 2015).

The sow’s behavior greatly influences the litter’s nursing behavior. During parturition, sows mainly lie in lateral recumbency with udders exposed for piglets to nurse at any time. Sows will emit deep rhythmic grunts when lying in the nursing position, and these grunts gradually transform to be distinctive and solely associated with nursing bouts as colostrum and milk ejection become strictly cyclical (de Passillé and Rushen, 1989). During established lactation, the sow’s vocalizations signal to the piglets when a new nursing bout is starting. These vocalizations are not only important for the individual sow’s litter but will also stimulate the onset nursing for other nearby sows when sows are housed in groups of at least 3-4 per room/area (Špinka and Illmann, 2015). Thus, lactational vocalizations from the sow serve as communication means between sow and litter, as well as between neighboring sows.

Teat Ownership

Piglets actively compete for resources through teat disputes. Within hours after birth, teat sampling becomes a competition for ownership over specific teats. Earlier born piglets, heavier piglets and piglets originally at the targeted teat typically win more disputes, which is

23 advantageous for early teat ownership (de Passillé and Rushen, 1989). Teat ownership increases over the first few days postpartum, from 5-50% of the litter claiming ownership by day 1 to 85-

95% claiming ownership by day 4 postpartum (de Passillé et al., 1988). Early teat ownership is greatly beneficial for piglets. A piglet that has claimed a specific teat will return to that teat and defend it for successive nursing bouts, ensuring colostrum/milk intake during nursing. However, piglets still disputing for teats typically do not consume as much colostrum and expend more energy competing with their littermates, consequently leading to starvation and death (Špinka and Illmann, 2015).

Once teat ownership has been established by day 7 of lactation, piglets primarily suckle from their respective teat or teat pair for the remainder of lactation (de Passillé and Rushen,

1988). It has recently been observed that a fair amount of variation exists regarding teat ownership. Although teat order seems to be relatively stable after week 2 of lactation (Špinka and Illmann, 2015), piglets may nurse from nearby nipples throughout lactation, and this variation is especially noted with rear nursed teats and once milk letdown ceases (Lannom, 2018;

Kim et al., 2000). Previous studies have observed that the 2nd, 3rd, and 4th pairs, are most competed for (de Passillé and Rushen, 1989; Kim et al., 2000). However, most recently,

Lannom (2018) recorded that the two most anterior teat pairs are nursed most consistently by piglets, and that significantly greater variation exists with all other teat pairs.

It has been suggested that anterior teats are most sought after either because they produce more milk (Kim et al., 2000) or because piglets are more attracted towards the sow’s grunts

(Devillers et al., 2016). It has recently been observed that neonatal piglets can distinguish between more productive and less productive teats, indicating that higher preference for anterior teats is likely due to anterior teats being more productive (Devillers et al., 2015). It has also been

24 reported that piglets nursing the first 5 pairs of anterior teats have faster pre-weaning growth than pigs nursing posterior teat pairs (Kim et al., 2000). A second study reported that pre-weaning survival, weaning weight, and pre-weaning weekly weight gain all significantly decrease as pigs nurse more posterior teats (Lannom, 2018).

Piglet Pre-Weaning Mortality

A singular cause for piglet mortality is difficult to distinguish, as mortality is highly multifaceted. Maternal, piglet, and environmental factors all contribute to piglet mortality, and often a combination of factors are responsible. Understanding factors that predispose piglets to pre-weaning mortality as well as factors that directly or indirectly lead to early postnatal death can aid in implementing new measures to decrease piglet pre-weaning mortality.

Total piglet mortality includes live-born and stillborn deaths that occur before weaning.

Pre-weaning mortality, as well as additional information gathered during farrowing and lactation can be summarized for an entire herd with proper record keeping. This summary can then be used to assess the herd’s performance over a given period of time by comparing past performance and using production reference standards and decision boundaries. Reference standards refer to acceptable levels of production, and decision boundaries are levels at which management changes should be initiated to improve performance. According to a National Pork

Board report, pre-weaning mortality has averaged 17.3-20.5% since 2013, and with current estimates (2017) being 17.8% (2018). The industry accepted reference standard and decision boundary for pre-weaning mortality are <8.0% and >12.0%, respectively, which illustrates the importance of increasing piglet survival. Although the three main reported causes of mortality are stillbirths, crushing by the sow, and starvation (Edwards and Baxter, 2015), these causes are

25 undoubtedly influenced by a variety of factors, which is indicative of the complexity of finding solutions for piglet mortality.

Factors that Contribute to Pre-Weaning Mortality

Maternal factors contributing to piglet pre-weaning mortality include intrauterine effects, farrowing characteristics, colostrum availability, and maternal behavior. Competition for resources begins in utero for the piglets, especially when there is overcrowding. Hyperprolific sow lines have intensified this occurrence, as uterine crowding has been shown to restrict fetal development when the number of embryos exceeds 14 (Dziuk, 1968). Both asynchronous elongation and intrauterine growth restriction (IUGR) are innate homeostatic mechanisms that occur in sows when the number of fetuses exceeds uterine capacity (Edwards and Baxter, 2015).

Overcrowding prompts disproportionate allocation of nutrients in utero, resulting in differential rates of development among conceptuses. Conceptuses, remarkably, can alter the uterine environment through secreting estradiol 17β (Špinka, 2017). Prior to and during conceptus elongation, more developed conceptuses have been reported to release estrogen, which appears to hinder proper elongation of less developed conceptuses.

Furthermore, uterine crowding can cause IUGR, which greatly impedes proper fetal development, and can cause fetal death and reduced viability in neonatal piglets. IUGR is characterized by significant within-litter variation, with growth-restricted fetuses weighing substantially less than their littermates. It has been shown that IUGR piglets fall into a separate subpopulation of low birthweight animals, which can typically be identified by birth weights less than two standard deviations of the mean litter birth weight (Foxcroft and Town, 2004; Ji et al.,

2017). Moreover, IUGR results in asymmetric fetal growth, with relative sparing of the brain at the expense of other fetal organs (Town et al., 2004). This disproportionality reveals that IUGR

26 piglets are not only smaller than their littermates, but in fact have compromised organ development. Thus, there is an important distinction between small for gestational age (SGA) piglets and IUGR piglets. SGA piglet are classified by weighing less than the 10th percentile but having normal allometry, which gives them a better chance of recovery and survival compared to

IUGR piglets (Edwards and Baxter, 2015).

Uterine capacity becomes a limiting factor for fetal growth and survival after day 25 of gestation, with the greatest effects occurring between days 30-40 of gestation (Foxcroft et al.,

2006). Interestingly, Meishan sows can produce significantly larger litters (12.0 born alive versus 10.6 and 11.6 for Large White and Duroc x Large White crosses, respectively) with significantly low (3%) proportion of stillbirths compared to Large White and Large White Duroc cross breeds (Canario et al., 2006). Meishan sows have been reported to overcome uterine crowding through increased placental efficiency, which is thought to be due to an increased density of blood vessels in their placentae (Edwards and Baxter, 2015). Although Meishan birthweights are typically reduced, piglets are born more developmentally proportionate, better preparing them for neonatal survival.

The duration and difficulty of farrowing can directly influence the number of stillbirths

(Edwards and Baxter, 2015). The average duration of farrowing ranges from 156 to 262 minutes

(van Dijk et al., 2005), and lengthier farrowings result in significantly higher stillbirth rates (van

Dijk et al., 2005; Edwards and Baxter, 2015). Larger litter sizes, fatigue, and high ambient temperatures have all been reported to significantly increase the duration of farrowing (Edwards and Baxter, 2015). Piglets in lengthier farrowings, especially when in the last third of the birth order, are more likely to be deprived of oxygen and either die of asphyxiation or be less viable because of hypoxia. Farrowing difficulty can be partly characterized by the birth interval, which

27 is the interval of time between each piglet birth. Birth intervals range from 15.1 to 28.5 minutes, on average (van Rens and van der Lende, 2004), but are highly variable both within litters and across sows. Increased birth weight and stillborn piglets are associated with significantly longer than average birth intervals (van Dijk et al., 2005), and birth intervals have been shown to increase as farrowing progresses (van Rens and van der Lende, 2004). In addition, older parity sows consistently produce more stillbirths than first-, second-, and third-parity sows (Edwards and Baxter, 2015). The prevalence of stillbirths can have a lasting effect, as sows with high stillbirths will likely be prone to stillbirths in subsequent litters (Roehe et al., 2010).

Maternal behavior of the sow relates to colostrum and milk availability, as the sow must expose her underline for piglets to initiate and complete their nursing bouts. Sow restlessness hinders colostrum and milk intake by the piglets; prolongs farrowing; and increases the incidence of crushing (Edwards and Baxter, 2015). Another maternal behavior important for piglet survival is the sow’s responsiveness to her piglets, where responsiveness refers to the sow’s actions towards her piglets. Highly responsive sows easily expose the underline for piglets to nurse and will change posture to prevent crushing of piglets. Unresponsive sows display more lateral lying, which inhibits suckling, and do not respond to their piglets’ squeals to reduce crushing

(Jarvis et al., 1999). Less responsive sows contribute to the hypothermia-starvation-crushing complex, exacerbating the risk of mortality already present for compromised piglets (Edwards and Baxter, 2015). Lastly, the sow’s temperament influences piglet survivability. Sows that are more nervous around humans and/or their young typically have increased reactivity and crush more piglets. Piglet mortality or injury from savaging can result from increased maternal nervousness and be accompanied by decreased udder access, predisposing piglets to starvation or crushing (Edwards and Baxter, 2015).

Piglet factors contributing to pre-weaning mortality include size, behavior, thermoregulatory abilities, and gender. Birth weight is accredited for being the primary determinant of live-born survival (Edwards and Baxter, 2015), as low birth weight piglets can be at greater risk for pre-weaning mortality. Roehe and Kalm (2000) demonstrated this by reporting

40% pre-weaning mortality for birth weights less than 1 kg, 15% pre-weaning mortality for birth weights between 1-1.2 kg, and a low 7% pre-weaning mortality for birth weights above 1.7 kg.

Low birth weight and IUGR piglets can have compromised organ development, which decreases vigor and can impede ingestion and digestion of colostrum. Therefore, even if less active IUGR piglets can obtain colostrum, they might not be able to utilize its biological properties. This inability to absorb colostrum is due to gut closure, which occurs at approximately 48 hours postnatally in piglets (Cranwell, 1995). Thus, there is a critical window for gut permeability of macromolecules in colostrum, most notably immunoglobulins. It is imperative that piglets consume adequate amounts of colostrum before the gut closes, especially for acquisition of passive immunity. It is generally accepted that there are two defined windows of opportunity for pathogens to invade the piglet’s systemic circulation. The first 24 hours postnatally and the transition from passive to active immunity – both of which occur early in lactation (Edwards and

Baxter, 2015). Inadequate colostrum consumption directly inhibits the piglets’ immunity to pathogens during this time, thus illustrating the importance of piglets getting adequate and timely colostrum intake.

Vigor, or vitality, refers to a piglet’s survival behavior, which can be highly variable in neonatal piglets (Edwards and Baxter, 2015). Several neonatal behaviors can be used to define vitality, including movement capacity, interval between birth and first suckling, and piglet screaming (Muns et al., 2013; Baxter et al., 2008). A piglet displaying low movement capacity

29 is unable to keep a voluntary position or unable to move, while a piglet with high movement capacity can turn its body axis >90° from its initial orientation within 15 seconds. Low vitality piglets take between 44-61 minutes, on average after birth to suckle while high vitality piglets first suckle within 27-30 minutes, on average after birth (Baxter et al., 2008). The occurrence of piglet screaming reflects the piglet’s ability to signal distress calls to the sow and prevent crushing, with lack of screams and presence of screams during manipulation representing low and high vitality piglets, respectively (Muns et al., 2013). Piglets displaying more vigor are associated with greater neonatal activity, greater colostrum consumption, and less crushing, resulting in improved survivability (Edwards and Baxter, 2015). In fact, small but vigorous piglets are equally as likely to survive the lactation period as their larger littermates (Baxter et al., 2008). Heavier piglets at birth are typically associated with greater vitality and winning more teat competitions. This allows for timely establishment of teat ownership and greater suckling frequency than lighter littermates (De Passillé and Rushen 1989). Thus, larger and more vigorous piglets clearly have an advantage when competing for resources during lactation.

Nursing behavior influences piglet mortality through the consequences of teat competitions. The emphasis placed on hyperprolific sows has only exacerbated the consequences of teat competition, as larger litters typically have lower birth weights and much intra-litter birth weight variation. Thus, larger litters produce more piglets born at a disadvantage for securing teat ownership (Špinka and Illmann, 2015). An added concern is the amount of colostrum available for consumption. Colostrum yield is not dependent on litter size, meaning that sows producing larger litters do not produce more colostrum to compensate. In fact, colostrum consumption per piglet decreases by approximately 10% with each added piglet (Devillers et al.,

2007), making early teat ownership even more crucial. Moreover, piglets nursing from posterior

30 teats have significantly reduced weekly weight gain and survival compared to piglets nursing anterior teats. Specifically, piglets nursing the two most posterior teat pairs have reduced weight gain throughout each week of lactation compared to piglets nursing the three most anterior teat pairs. Piglet pre-weaning survival is significantly reduced from piglets nursing the two most anterior teat pairs compared to those nursing the three most posterior teat pairs (>93% versus

<87%, on average, respectively) (Lannom, 2018).

Impaired thermoregulation leads to hypothermia in the piglet, which is considered a primary cause of pre-weaning mortality (Edwards and Baxter, 2015). Newborn piglets do not possess proper thermoregulatory abilities because they are born mostly without hair and lack brown adipose tissue needed for heat production (Herpin et al., 2002). In addition, piglets experience a drastic change in environmental temperature at parturition, as there is typically a

15-20°C difference between the sow’s core temperature and the ambient temperature of the farrowing room. Thus, neonatal piglets are easily prone to chilling. Birth weight influences the piglet’s risk of chilling. Smaller piglets are at greater risk of hypothermia because more heat is lost per unit of body weight (Herpin et al., 2002). Thermoregulatory ability, like many other factors influencing mortality, is dependent on colostrum intake. Adequate colostrum intake and metabolism ensures proper initiation and maintenance of thermoregulation (Edwards and Baxter,

2015).

It has been reported that male piglets have a reduced chance of pre-weaning survivability compared to female piglets (Baxter et al., 2012). This difference is not related to birth weights, but rather compromised thermoregulatory abilities (Baxter et al., 2012). The cause of this impaired thermoregulation in male piglets has not been entirely determined, but it is thought to be due to energy allocations in the neonatal pig or insufficient colostrum consumption (Baxter et

31 al., 2012). Male piglets may direct more energy towards body size and composition during early neonatal hours, while female piglets may be directing more energy towards specific physiological systems. Additionally, male piglets may have a decreased nursing frequency and duration during the colostral period or may be more likely to suckle from less productive teats.

Lastly, because male piglets typically have larger birth weights and thus increased metabolic demands, they may be expending more energy massaging teats in an attempt to yield more milk during each nursing bout.

It is clear that physiological challenges, resulting from low vigor, starvation, or hypothermia increase the risk of crushing due to lethargic piglets being unable to escape the moving sow and/or from piglets residing in crushing-risk areas. In addition, piglets with slower weight gain are more likely to remain in crushing-risk areas, such as underneath the sow.

Moreover, inadequate colostrum intake impairs the piglet’s ability to escape from crushing, by not providing the neonate with proper energy. Once again, it is highly evident that ingestion of colostrum is necessary for piglet pre-weaning survival.

Management Interventions to Increase Survivability

Many factors contributing to pre-weaning mortality can be partially combatted by management strategies. These include providing proper farrowing and neonatal pig management and decreasing competition for resources within litters (Edwards and Baxter, 2015). Farrowing induction is a commonly used approach that helps synchronize farrowings and ensure enough staff are present on farrowing days. Successful farrowing induction allows for monitoring and assisting of sows during farrowing, which has been shown to decrease the rate of stillbirths

(Edwards and Baxter, 2015). Induction also results in a more uniform weaning, which is beneficial for the type of management system commonly used on sow farms, termed ‘all in, all

32 out’ management. For ‘all in, all out’ management, all sows in a group are simultaneously moved in and out of the farrowing barn, and it is beneficial for sows to be on the same weaning schedule to facilitate this.

Induction can be carried out by administering a prostaglandin prior to the farrowing date to increase the synchrony of farrowing. When prostaglandins are administered correctly to induce farrowing, they typically cause an earlier mean onset of farrowing and reduced variation in farrowing dates (Kirkden et al., 2013). Conversely, when sows farrow naturally, the farrowing dates for a group of sows can spread over a period of 10 days (King et al., 1979), making farrowing monitoring and neonatal pig management difficult. When farrowing is induced between days 111-114 days of gestation, between 40% and >90% of sows will farrow during the next 8-12 hour working day (Kirkden et al., 2013). The timing of treatment, number of doses administered, and degree of sow disturbances can affect the degree of synchrony. Inducing after day 111, giving two prostaglandin injections 6 hours apart, and reducing farrowing room disturbances may all aid in increasing the effectiveness of synchronization (Kirkden et al., 2013).

Induction alone does not have any clear effects on piglet mortality, as studies have yielded varied results (Kirkden et al., 2013). However, differences in farrowing supervision clearly influences stillbirth and live-born mortality when combined with induction protocols. Studies have consistently shown that increased supervision results in significantly increased piglet survival

(Kirkden et al., 2013; Nguyen et al., 2011; Holyoake et al., 1995). In addition, artificial insemination protocols can influence induction synchrony. Great success has been reported from using a single fixed-time artificial insemination protocol combined with induction on day 113 of gestation (Kraeling and Webel, 2015). Following this protocol, more than 80% of treated sows

33 farrowed on the same day and 92% of treated sows farrowed within 2 days compared to 38% for controls (Webel et al., 2014).

Caution should be taken when inducing sows as incorrect induction can have drastic consequences. Piglets go through a phase of increased growth and development, notably lung maturation, during the final days of gestation. Therefore, parturition should not be induced before day 113 of gestation so that birthing complications and compromised neonatal survival are avoided (Kirkden et al., 2013). Furthermore, gilts should not be induced, as they experience more gestation length variation than sows (Kirkden et al., 2013). Pharmacological intervention can also be practiced during farrowing by administering oxytocin to combat farrowing fatigue.

However, misuse of oxytocin can increase fetal asphyxia and increase stillbirths (Edwards and

Baxter, 2015).

Proper management of newborn pigs can help combat pre-weaning mortality (Edwards and Baxter, 2015). A primary concern for neonatal piglets is their lack of ability to thermoregulate. Thus, it is imperative that farrowing barn temperatures and supplemental heat sources are managed in such a way to assist the piglets with thermoregulation. During farrowing and the first few days following, temperatures of piglet areas should be kept between 90-95°F.

After that, temperatures should be adjusted accordingly depending on the behavior of the piglets

(England et al., 2019). Although these are optimal temperatures for piglets, ambient temperature of the farrowing barn needs be kept at less than 80°F to prevent the sows from getting heat stressed. To achieve optimal temperatures for both sows and piglets, the farrowing barn ambient temperature should be kept between 70-80°F, and supplemental heating equipment should be used in piglet areas. Both heating lamps and heating mats can be used as supplemental heat sources in farrowing crates. While both can be effective heating options, it has been shown that

34 piglets may prefer heating lamps over heating mats during the first two days after birth, which is expected because radiant heat is more effective at drying off birth fluids (Zhang and Xin, 2001).

After this, heat source preference does not significantly differ between lamps and mats (Zhang and Xin, 2001; Xin and Stinn, 2014). Average weight gain and pre-weaning mortality do not significantly differ for either source (Xin and Stinn, 2014; Beshada et al., 2006). Conversely, heating mats are more energy efficient than lamps, as mats have been shown to save over 50% in energy costs compared to lamps (Xin and Stinn, 2014; Beshada et al., 2006). Thus, although piglet performance does not significantly differ between heat sources, heating pads are more cost effective for farrowing crate use.

Additionally, drying off newborn piglets may be an effective management strategy to help prevent chilling (Andersen et al., 2009). Although solely drying off newborn piglets may not affect piglet mortality, it has been shown to effectively increase rectal temperatures and decrease latency to suckle (Kirkden et al., 2013). Additionally, drying off piglets and placing them under heat lamps has been reported to significantly decrease postnatal mortality, especially due to crushing (Andersen et al., 2009). This combination is likely most important for inactive piglets, which have lower heat production and do not seek out heat sources (Kirkden et al.,

2013).

Strategic cross-fostering, split suckling, artificial rearing, and milk supplementation are additional management strategies used to improve piglet health. These remaining interventions specifically help to better allocate resources for large litters and litters with significant weight variation. Interestingly, within-litter variation may be more important for determining piglet survival than birth weight (Edwards and Baxter, 2015). Because larger piglets win more teat disputes and establish ownership of teats faster than smaller littermates, intra-litter weight

35 variation leaves smaller piglets at a significant disadvantage, especially when the number of piglets exceeds functional teats.

Cross-fostering is commonly used on sow farms, and when done correctly, enhances piglet survival (Edwards and Baxter, 2015). If cross-fostering is implemented, it should be done in such a way that allows piglets to obtain adequate amounts of colostrum (i.e. not moving piglets too early) and prevents excessive teat competition (i.e. not moving piglets too late).

Repeated cross-fostering of the same piglet is not recommended, as it disrupts both the nursing order and suckling episodes (Edwards and Baxter, 2015). Successful cross-fostering requires uniform farrowings to allow for colostrum consumption and equal allocation of resources between piglets, and this can be accomplished through farrowing induction. Farrowing induction allows for timely cross-fostering between litters that have farrowed on similar dates, which is most recommended.

Split-nursing is a common practice in Denmark and the Netherlands used to combat the challenges of large litters (Edwards and Baxter, 2015), although it has not been largely adopted in other countries. Artificial rearing systems are also used in the Netherlands and in the United

States to separate surplus or low viability piglets from the rest of the litter. Piglets are moved to an elevated surface at day 3 of lactation and provided with heat, lighting, artificial milk, and water. Although artificial rearing has been reported to improve piglet survivability (Van Dijk,

2012), further research is needed to determine the system’s overall implications.

Providing artificial milk replacer to litters is an effective management strategy, and colostrum supplementation during early postnatal life may also be effective. When artificial milk replacer was supplemented from day 3 of lactation until weaning, piglet weights were significantly increased each week of nursing compared to non-supplemented piglets (Quesnel et

36 al., 2015). Orally supplementing low birth weight (less than 1.35 kg) piglets with colostrum within 4 hours postpartum increased piglets’ IgG levels at day 4 (Muns et al., 2014), potentially enhancing piglet immunity and resistance to pathogens.

Lastly, genetic selection for traits associated with lactation and piglet growth also appear to be viable approaches for reducing pre-weaning mortality. Recently, selecting for traits related to neonatal survival has successfully improved piglet survival rates, reflected by an average perinatal survival of 96.4% compared to the literature average of 82-95.6% (Roehe et al., 2010).

Selecting for live piglets at postnatal day 5 (LP5) instead of total born resulted in an increase of

2.3 pigs weaned/litter (Su et al., 2007). Furthermore, reduced intra-litter birth weight variability

(Huby et al., 2003), improved placental efficiency (Van Rens et al., 2005), and improved maternal behavior (Baxter et al., 2011) may be possible selection criteria to increase piglet survival.

Conclusion

The sow’s natural biology presents a significant challenge for reducing pre-weaning mortality, as competition for resources within litters arises in utero and continues throughout lactation. Although many beneficial management practices are being utilized on sow farms, pre- weaning mortality remains high. It is well documented that most pre-weaning deaths occur during the first few days of lactation. Thus, further research is needed to determine what other factors influence mortality during this time, and how these factors can be manipulated to increase piglet survival. Of particular interest is whether piglet birth order and birth interval affect which teats piglets choose to nurse, and consequently if this influences their growth and survival, which was the primary objective of the research contained in this thesis.

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INTRODUCTION Piglet pre-weaning mortality currently averages 17.8% among U.S. swine farms which is considered high, and it appears to have been increasing over the past several years (National

Pork Board, 2018). Although many factors influence pre-weaning mortality, birthweight and colostrum consumption are considered two of the most important determinants (Edwards and

Baxter, 2015). It has recently been shown that the anatomical location of teats piglets nurse affects both pre-weaning survival and growth performance (Lannom, 2018). In this study, as piglets nursed more posterior pairs of teats, their growth and survival decreased, and these effects were independent of birthweight. One possible explanation for this was that the nutritional and immunological quality of colostrum after farrowing was highest for anterior teats and lowest for posterior teats (Lannom, 2018). Other studies have reported that colostrum quality decreases considerably during the first 24 hours post farrowing (Hurley, 2015), but whether these decreases are consistent for all teats is not known. This information could provide a better representation of colostrum quality available to piglets shortly after birth and may give additional insight to the differences in pre-weaning performance associated with teat location.

Another factor thought to influence survival is the activity level, or vigor of piglets, immediately after birth. Previous studies have attributed differences among piglet vigor after birth to colostrum consumption (Baxter et al., 2008; Herpin et al., 2002; Tuchscherer et al.,

2000). However, piglet vigor may be related to hypoxia, which is influenced by the length of time it takes the sow to push piglets through the birth canal (van Dijk et al., 2005; Edwards and

Baxter, 2015). Currently, there are no published studies that have examined aspects associated with parturition in conjunction with nursing activities and colostrum quality on piglet pre- weaning growth and survival. Additional research is needed to provide a more comprehensive

45 understanding of how these factors may interact to influence pre-weaning survival and growth.

Therefore, the primary objective of this study was to determine the relative importance of various factors associated with the perinatal environment of piglets on their pre-weaning survival and growth performance. Of particular interest were characteristics associated with the timing and birth order during parturition and whether these factors influence teat selection. Secondary objectives were to evaluate the effectiveness of administering an oral gavage of high-energy milk replacer within 24 hours after birth on subsequent pre-weaning survival and growth and to evaluate the compositional changes of colostrum over time and across different teat pairs.

MATERIALS AND METHODS

Animals, Facilities, and General Management

The study was conducted at the Swine Educational Unit (SEU) at North Carolina State

University. The SEU is a closed herd, farrow-to-nursery operation with 250 sows. All females used in the study were Smithfield Premium Genetics (SPG) maternal-line sows that farrowed litters sired by SPG terminal-line boars. Sows were moved to farrowing crates at approximately day 107 of gestation. Each farrowing room consisted of 12 individual, bow-bar crates that measured 1.5 m wide by 2.5 m long. The flooring in the farrowing crates consisted of either

TriBar®, an expanded metal, or Tenderfoot®, a plastic-coated wire. Each room had a propane heater suspended from the ceiling for general heating purposes and each farrowing crate had two heat lamps in order to provide supplemental heat for the piglets. Ventilation for each room was provided by a side-wall baffle ventilation system with an evaporative cooling cell. An under-slat flush system was used for waste removal. During lactation, sows were fed a corn and soybean formulated ration ad libitum twice per day that was formulated to meet or exceed NRC recommendations for lactating sows at a daily feed intake of 6.36 kg (NRC, 2012).

Piglets were processed within 24 hours of parturition. The standard operating procedures for processing piglets included ear notching, clipping needle teeth, docking tails, administering oral antibiotics (Spectam; Bimeda, Oakbrook Terrace, IL, USA) and injecting iron (Uniferon

100; Pharmacosmos Inc., Copenhagen, Denmark), and penicillin (Norocillin; Norbrook, Lenexa,

KS, USA). Body weight and sex for all piglets were also recorded. Cross-fostering occurred between 24 and 48 hours after birth and after all piglets were processed. Piglets were distributed in a manner such that each sow was nursing 10-12 piglets after cross-fostering. Male piglets were castrated at 6 days of age. Access to milk replacer (Calf Milk Replacer Non-Medicated;

Sav-A-Caf, Chilton, WI) was provided ad libitum beginning at day 7 of lactation to litters nursing sows whose milk production was deemed to be suboptimal by the SEU management. All piglets were weaned at 22 days of age.

Experimental Procedures

All experimental procedures performed on the sows and piglets during this study were approved by the N.C.S.U. Institutional Animal Use and Care Committee (18-101-A). Data was collected from sows (n=61) first and their litters (n=789 piglets) across seven different production groups that farrowed between October, 2018 and May, 2019. Parturition was synchronized with 2.5 mL of a prostaglandin analogue (Lutalyse, Zoetis, Kalamazoo, MI, USA) administered on day 113 of gestation to sows whose historical average was 114 days. This resulted in all sows used in the study farrowing on the same day of the week (Wednesday) which was designated as day 0 of lactation. Sows were monitored continuously during farrowing and manually checked for the presence of piglets in their birth canals when they were in obvious distress or when the birth interval between consecutive piglets exceeded 30 minutes. Piglets encountered during these examinations were removed manually. Fetal membranes were removed; respiratory activity was assessed and stimulated if necessary; and a drying agent

(Mistral, Olmix Group, Brittany, France) was applied to all piglets immediately after they were born regardless of whether they were manually removed or delivered without human assistance.

In addition, a unique combination of different-colored zip ties (0.2 x 10.2 cm, Staples Office

Supply, Raleigh, NC) were placed securely on the posterior one-third of each piglet’s tail (Figure

1). This provided a temporary form of identification until piglets received their ear notches at processing. Data recorded at birth for each piglet included the following: time of birth; birth order; presence of meconium (Figure 2); presence of umbilical hematomas (Figure 3); and

48 whether they were born naturally or removed manually. The anatomical location of teats suckled by piglets was also recorded even though nursing activity was sporadic in most litters while sows were farrowing. Parturition was considered to be finished once sows passed their placental membranes and a manual examination of the reproductive tract did not detect additional piglets.

Data recorded for each litter after farrowing was deemed to be over included the following: length of farrowing; number of piglets born alive; number of stillborn piglets; number of mummified fetuses; total number of pigs born; and number of piglets fostered.

Piglets were weighed at processing which was designated as day 1 of lactation and on days 8, 15 and 22. Nursing observations were recorded during farrowing (day 0) and on days 1,

8, 15 and 21 of lactation. Before each nursing observation period the back of each piglet was marked with different color crayons (All-Weather Paint Stick, QC Supply, Schuyler, NE) in order to facilitate data collection (Figure 4). Colors for each pig were assigned randomly. After being marked, the entire litter was returned to their sow and the teat that each piglet nursed was recorded during two to three consecutive nursing bouts for each observation period. A nursing bout was considered to begin when the sow was laying on her side with her underline exposed and all the piglets were attempting to nurse a teat. It was considered to end when the sow rolled over with her underline underneath her body or when she stood, and the piglets moved away from her. If a piglet started nursing one teat and then switched to another one, then the piglet was given credit for nursing two teats during that nursing bout and the sequence in which the teats were nursed was recorded. Nursing bouts lasted between 45 and 240 seconds.

A subset of piglets within each litter was used to examine the effect of an oral gavage of milk replacer on pre-weaning survival and growth. Pairs of piglets with similar birth weights that were nursing either the first two or last three pairs of teats were randomly assigned to control or

49 milk replacer treatments. The milk replacer treatment (Calf Milk Replacer Non-Medicated; Sav-

A-Caf, Chilton, WI) was prepared in a concentrated form such that 1 mL contained an average of

890 ± 7 calories. The estimate of all the nutrients in the dose of milk replacer is contained in

Appendix B. An 8-ounce plastic bottle fitted with a single dose pump action dispenser was used to administer the concentrated milk replacer. Treated piglets (n=204) received an oral gavage of

1 mL between 12 and 24 h after birth. Control piglets (n=205) were picked up and held for about

20 s which was the length of time required to administer the oral gavage to treated pigs and then returned to the litter.

Colostrum samples were collected from sows (n=8) in the May (2019) farrowing group.

Samples were collected without the use of oxytocin between 1 and 4 hours prior to farrowing and again after administration of 10 IU of oxytocin between 20 and 24 hours after the onset of farrowing from the first two and last two pairs of teats. Teats at each anatomical location were gently massaged until colostrum was expressed. Samples were pooled across both teat pairs at each anatomical location and stored in triplicate at 4°C immediately after collection until they were sent to a commercial laboratory for subsequent analyses.

Colostrum Composition Analyses

The commercial laboratory was a GLP certified facility and used techniques in accordance with the Association of Official Analytical Chemists for determination of dry matter, ash, fat, protein and lactose composition of samples (AOAC, 1990). The laboratory used the

Babcock method to estimate the percentage of fat. Protein was determined by measuring nitrogen using pyrolysis and quantification of N2 (Dumas method) and then multiplication of the N content by 6.38. Lactose was assayed using an enzymatic method (LECO TFE-2000).

Immunoglobulins G, A, and M were analyzed by ELIZA using commercially available kits

(Bethyl Laboratories, Montgomery, TX) for porcine IgG and IgA and human IgM.

Immunoglobulins were assayed in duplicate. The intra- and interassay coefficients of variation were 4.7 and 9.5% for IgG; 4.8 and 10.4% for IgA; and 7.2 and 11.6% for IgM, respectively.

Statistical Analyses

The primary objective of this study was to determine relative contributions of factors associated with perinatal environment of piglets on their pre-weaning success. Dependent variables used to estimate pre-weaning success were as follows: weight gain between days 1 and

7 (kg); weight gain between days 7 and 14 (kg); weight gain between days 14 and 21 (kg); weight gain between days 1 and 21 (kg); weaning weight (kg); percentage of piglets that survived from birth to 7 days of age; and the percentage of piglets that survived from birth until weaning at 21 days of age. Variables used to characterize the perinatal environment included the following: sow parity; total number of pigs born; length of farrowing (min); birth order of piglets; birth of piglets relative to onset of farrowing (min); presence of meconium on piglets at birth; presence of umbilical cord hematomas at birth; whether the piglet was manually removed during farrowing; birth weight (kg); first pair of nipples piglets nursed immediately after birth; whether piglets were given an oral gavage of supplemental milk during the first 24 h after birth; pair of nipples nursed most frequently during entire lactation; nursing consistency which was defined as the proportion of observed nursing bouts during which piglets nursed their favorite pair of nipples (%); total number of pigs nursing; whether supplemental milk was provided for the entire litter after the first week of lactation; and number of pigs weaned. The decision to provide supplemental milk to the entire litter after day 7 of lactation was a standard operating procedure for the farm on which the study was conducted. Supplemental milk was provided to litters with > 50% of piglets with weight per day of age < 230 grams.

Initially, multiple regression analyses using SAS (SAS Institute, Inc., Cary, NC) were performed to determine the relative contributions of the independent variables listed previously on the pair of nipples selected to nurse most often and pre-weaning growth and survival of piglets (Snedecor and Cochran, 1998). The inclusion criterion for main effects to enter the model was p < 0.15. Based on these results, piglet birth weight; sow parity; nursing consistency; pair of nipples nursed most during lactation; length of farrowing; birth of piglet relative to the onset of farrowing; presence of umbilical hematomas; supplemental milk for individual pigs between 12 and 24 hours of birth; and supplemental milk for the entire litter after the first week of lactation were selected for subsequent analyses.

Data for piglet birth weight; sow parity; nursing consistency; length of farrowing and birth of piglets relative to the onset of farrowing were partitioned post priori into three groups.

For piglet birth weight and birth of piglets relative to the onset of farrowing the three categories were piglets that were less than; greater than; or within one standard deviation of the overall population mean. For sow parity, the three groups were parity 2; parities 3 through 6; and parities greater than or equal to parity 7. These were based upon previously reported and commonly accepted age-related production differences (Flowers, 1999). A similar approach was used for length of farrowing with the three groups being less than 3 hours; 3 to 6 hours; and greater than 6 hours. These groups also were based on previous studies examining the incidence of hypoxia in neonatal piglets (Herpin et al., 1996). In contrast, nursing consistency groups were created such that each subset had equivalent numbers of observations since this was a novel variable that has not been studied extensively. The anatomical location of the teat nursed most often and whether or not piglets were manually removed during farrowing; received supplemental milk; or had

52 umbilical hernias, respectively, served as the grouping criteria for each of the remaining variables.

Next, the effect of each of these variables on piglet survival and growth characteristics was determined individually. For piglet growth characteristics, analyses were conducted using mixed model procedures in SAS (PROC MIXED; SAS; SAS Institute, Cary, N.C.) with a statistical model that included the variable of interest and farrowing group as the main effects with all other independent variables treated as covariates (Littel et al., 1996). A similar approach was undertaken for survival rate with the exception that mixed model procedures for categorical data (PROC GLIMMIX; SAS; SAS Institute, Cary, N.C.) were used (Koch et al., 1977). When significant main effects were present, Student-Newman Kuels multiple range test was used to determine differences among individual means (Snedecor and Cochran, 1989).

Concentrations of IgG (ug/mL), IgA (ug/mL) and IgM (ug/mL) and percentages of dry matter, ash, fat, protein, and lactose in colostrum were analyzed with mixed model procedures for repeated measures using SAS (Proc Mixed; SAS; SAS Institute, Cary, N.C.). The statistical model included teat location (first two pairs versus last two pairs) and time (0 to 4 hours prior to farrowing versus 24 hours after farrowing) and their interaction (Littel et al., 1996). Total number of pigs born alive and length of farrowing were used as covariates in the model. The variance/covariance adjustment was determined by finding the appropriate structure with the lowest fit statistics. The error term for teat location nested within sow was used to test for the main effect of teat location and its interactions and was considered to be a random effect.

RESULTS

Changes in Colostrum Composition

Changes in colostrum composition over time in the first two and last two pairs of teats are shown in Tables 1 through 8. Dry matter (Table 1), protein (Table 3) and IgG (Table 6) concentrations were higher in the anterior versus posterior teats (P < 0.0001) and decreased during the first 24 hours of lactation (P < 0.001). However, the magnitudes of these decreases were greater for the anterior than posterior teats resulting in a significant interaction between anatomical location and time for each of these estimates of colostrum quality (P < 0.05). Ash content (Table 5) was higher (P < 0.0001) in the anterior teats compared with their posterior counterparts and did not change over time (P = 0.6072). In contrast, it decreased (P = 0.0133) during the first 24 hours of lactation in the posterior teats (time x anatomical location, P =

0.0249). Fat (Table 2), IgA (Table 7) and IgM (Table 8) all decreased (P < 0.001) over time but were not different (P > 0.5059) between the anterior and posterior teats. In contrast, lactose

(Table 4) did not change over time (P = 0.4268) but was higher (P < 0.0001) in the anterior than posterior teats.

Teat Selection by Piglets

Multiple regression analyses revealed that piglet birthweight (P = 0.0021), total number of pigs born (P = 0.0520), birth order (P = 0.0589), and sow parity influenced (P = 0.0630) which pair of teats piglets nursed within the first 24 hours after birth, although these four variables collectively accounted for less than 3% of the total variation observed (model R2=0.0286; Table

9). Piglets weighing less than 1.09 kg chose to nurse the last two pairs of teats more frequently (P

≤ 0.05) and the first six pairs of teats less frequently (P ≤ 0.05) compared with their heavier counterparts (Table 10). The pair of teats nursed most frequently by piglets during all of

54 lactation was influenced the most by the pair of teats piglets nursed during the first 24 hours after birth (partial R2 = 0.9829; P < 0.0001) and whether piglets had an umbilical hematoma at birth

(partial R2 = 0.0001; P = 0.0929; Table 11). Piglets born with an umbilical hematoma (84.1 +

7.8%; n=40) tended to nurse (P ≤ 0.1) the last three pairs of teats during lactation compared with piglets born with a normal umbilical cord (21.4 + 1.8%; data not shown).

Piglet Pre-Weaning Survival

Multiple regression analyses revealed that birthweight (P ≤ 0.0095), oral gavage of milk replacer within the first 24 hours of life (P ≤ 0.0325), anatomical location of teats nursed during the first 24 hours after farrowing (P ≤ 0.0432) and throughout lactation (P ≤ 0.0473), and nursing consistency (P ≤ 0.0139) influenced piglet survival during lactation while all other variables did not (P ≥ 0.1; Table 12). Smallest birthweight piglets (≤ 1.09 kg) had lower survival (P ≤ 0.05) compared to their larger counterparts during the first week of lactation and throughout the entire pre-weaning period. During the third week of lactation, average-sized piglets (1.10 – 1.80 kg) had higher (P ≤ 0.05) survival rates compared with small piglets, and there were no mortalities for large piglets (> 1.80 kg; Table 13). Piglets nursing the most posterior teat pairs during the first 24 hours of lactation (Table 14) as well as throughout lactation (Table 15) had reduced survival rates (P ≤ 0.05) compared with piglets nursing other pairs over the same time periods.

Survival rates were 100% for piglets with a medium nursing consistency (73.9 ± 2.1%) during the first week of lactation, whereas piglets with low nursing consistencies (47.2 ± 4.8%) had improved survival rates (P ≤ 0.05) compared with those that had high nursing consistency (99.6

± 1.3%; Table 16). During the second week of lactation and throughout the pre-weaning period, piglets with high nursing consistencies had lower (P ≤ 0.05) survival rates compared with those with medium and low consistencies (Table 16). Piglets treated with an oral gavage of milk

55 replacer during the first 24 hours of life had greater survival (P ≤ 0.05) than their untreated contemporaries during the first week of lactation and, therefore, during the entire pre-weaning period (Table 17). Regardless of whether piglets were born early (3.2 ± 0.4 min), during the middle (94.2 ± 2.0 min), or late (273.8 ± 7.8 min) after the onset of farrowing, birth interval did not affect their pre-weaning survival (P ≥ 0.4456; Table 18).

Piglet Pre-Weaning Growth

Piglet weight gain during the first week of lactation (Table 19) was influenced by piglet birthweight (P < 0.0001); anatomical location of teats nursed throughout lactation (P < 0.0001); total number of pigs born (P < 0.0001); sow parity (P = 0.0061); length of parturition (P =

0.0294); and anatomical location of teats nursed during the first 24 hours of lactation (P =

0.09410). Collectively, these variables accounted for 26.4% of the observed variation in piglet weight gain during the first week of lactation. Piglet pre-weaning weight gain (Table 20) and weaning weight (Table 21) were influenced by piglet birthweight (P < 0.0001); anatomical location of teats nursed most often during lactation (P < 0.0001); total number born (P < 0.0001); access to supplemental milk after day 7 of lactation (P < 0.0001); the presence of umbilical hematomas (P = 0.0079); length of parturition (P = 0.1037); and anatomical location of teats nursed during the first 24 hours of lactation (P = 0.1276). These variables accounted for 32.0% and 45.5% of the total variation associated with pre-weaning weight gain and weaning weight, respectively.

Both piglet birthweight (Table 22) and anatomical location of teats nursed most during lactation (Table 23) exhibited a positive relationship with all of the pre-weaning growth traits.

For birthweight, large piglets (1.96 ± 0.1 kg) had better performance (P ≤ 0.05) compared with medium-sized piglets (1.48 ± 0.1 kg) which, in turn, experienced superior growth (P ≤ 0.05)

56 compared with small piglets (0.92 ± 0.1 kg). The best pre-weaning growth (P < 0.05) was observed for piglets nursing the first pair of teats. Piglets nursing pairs 2, 3, and 4 had superior growth and heavier weaning weights (P ≤ 0.05) compared with piglets nursing pairs 5 through 8.

Weaning weight and pre-weaning gain for piglets nursing pairs 7 and 8 were lower (P ≤ 0.05) compared with those of piglets nursing at other locations. There was a tendency for piglets nursing the first two pairs of teats to have better growth (P ≤ 0.1) during the first week of lactation compared with their counterparts nursing teats at other locations (Table 24). Piglets without umbilical hematomas at birth (Table 25) and given access to supplemental milk after day

7 of lactation (Table 26) had higher pre-weaning growth (P ≤ 0.007) and heavier weaning weights (P ≤ 0.007) compared with their respective contemporaries. Weight gain during the first week of lactation tended (P = 0.0798) to be improved for piglets without umbilical hematomas

(Table 25).

Sow parity affected piglet growth during the first week of lactation with piglets nursing sows in parities 3 through 6 having better performance (P ≤ 0.05) than those nursing second parity sows, while growth of piglets nursing sows parity 7 or higher was intermediate of these two groups (Table 27). There was a tendency for length of parturition to influence pre-weaning growth and weaning weights (Table 28). Those born in litters with an intermediate parturition length (230.4 ± 2.3 min) exhibited a tendency towards improved pre-weaning weight gain (P ≤

0.1) compared with those born in litters with short (137 ± 1.4 min) or long (423.3 ± 7.1 min) parturition lengths. A similar trend was observed for weaning weight except piglets born in litters with a short parturition were intermediate compared with their contemporaries born in litters with either medium or long parturitions. Birth interval (P ≥ 0.1589; Table 29), nursing

57 consistency (P ≥ 0.1772; Table 30), and an oral gavage of milk replacer within 24 hours of birth

(P ≥ 0.2070; Table 31) did not affect pre-weaning growth or weaning weights.

DISCUSSION

The primary objective of this study was to determine the relative importance of factors relating to the perinatal environment on piglet pre-weaning success. Additional objectives were to evaluate the effectiveness of supplying supplemental milk to piglets shortly after birth and to examine the compositional changes of colostrum over time and across different teat pairs.

Birthweight and the anatomical location of teats that piglets nursed were the main perinatal factors influencing pre-weaning growth and survival. As expected, low birthweight piglets and piglets nursing the most posterior teat pairs had reduced pre-weaning success. Administering an oral gavage of milk replacer shortly after birth improved pre-weaning survival by decreasing losses during the first week of lactation. The nutritional quality of colostrum declined both over time and for more posterior teat locations, and greater differences were observed across teat pairs for protein, lactose, and ash content.

The composition of colostrum has been evaluated at different time periods (Hurley, 2015) and recently from different teat locations on the underline (Lannom, 2018), however these have only been recorded separately. The present study extends the scope of current literature by revealing that the general quality of colostrum decreases both over time and for more posterior teat pairs, and that in many cases an interaction between the two exists. In agreement with previous data (Hurley, 2015; Lannom, 2018), dry matter and protein content decreased both over the first 24 hours of lactation and for more posterior teat pairs. While the quantities of these components were comparable to averages observed by previous studies (Hurley, 2015) when taken from anterior teat pairs, they were surprisingly lower than reported averages when taken from posterior teat pairs. In fact, samples taken from posterior teats at time 0 were already diminished to what is typically expected by 24 hours after farrowing. This suggests that previous

59 data only analyzing the composition of colostrum over time may not be a true reflection of colostrum from all teats, but instead may represent the enhanced quality found only in anterior teat pairs.

While it has commonly been observed that protein content declines by over 50% by 24 hours after farrowing (Hurley, 2015), the present study only observed a 14% reduction in protein content from anterior teats during this time period. In contrast, protein content was reduced by

68% and 65% for posterior teat pairs compared to anterior teat pairs at time 0 and time 24, respectively. The magnitude of these differences likely explains the reduced neonatal survival for piglets nursing posterior versus anterior teats. Protein concentration is largely mirrored by immunoglobulin content, which was supported by the present study’s findings, and immunoglobulins serve as a major source of immunity for piglets during early lactation

(Edwards and Baxter, 2015). The present study observed IgG content was distinctly reduced for posterior teat pairs, which is consistent with Ogawa et al. (2014), but contradicts Lannom’s

(2018) observations of no clear pattern for IgG content moving posteriorly down the underline.

Lactose and ash remained stable throughout the colostral period, which is consistent with previous literature (Hurley, 2015) but had a significant reduction going from anterior to posterior teats. This also conflicts findings by Lannom (2018) that lactose and ash do not significantly change across teat pairs. The differences in IgG and ash concentrations between the present study and Lannom (2018) may be due to variations in sampling time. Samples from Lannom

(2018) were taken at various times after the onset farrowing, while the present study grouped observations based on time relative to farrowing. Because of the significant interaction observed for ash and IgG content in the present study, the differences in anterior versus posterior teats may not be clearly seen without standardizing sampling time. The reduced quality of colostrum

60 observed from posterior teats may be explained by differences in mammary gland size (Kim et al., 2000). During lactation, anterior mammary glands have a larger mass than posterior glands, which corresponds to a greater amount of glandular tissue. Larger, anterior mammary glands contain more nutrient-synthesizing lactocytes (Martineau et al., 2012), which may explain the elevated nutrient content observed from these glands.

Although it has been generally accepted that fat content increases during the first 24 hours after farrowing (Hurley, 2015), the present study conversely found that fat content decreased during this time. This difference may be attributed to sampling time variation as well as variability across sows. Fat content has been observed to increase as colostrum transitions to mature milk, which typically occurs between 24 hours and day 3 of lactation (Theil et al., 2014).

However, the exact time of this occurrence can vary across sows. Thus, the smaller sample size in the present study may have captured more variability than that in the meta-analysis conducted by Hurley (2015).

Previous studies have shown that piglets choose specific teats to nurse early in lactation and typically nurse those teats throughout the remainder of lactation (de Passillé and Rushen,

1988; Špinka and Illmann, 2015). The establishment of a teat order is a fundamental nursing behavior in swine, but the reasoning behind this behavior has not been critically evaluated. It has been observed that anterior teats are the most competed for (de Passillé and Rushen, 1989; Kim et al., 2000; Lannom, 2018), and that piglets can distinguish between more productive and less productive teats (Devillers et al., 2016). The present study supports this by reporting that larger birthweight piglets preferentially suckled higher-quality colostrum from anterior teat pairs while lowest birthweight piglets suckled lower-quality colostrum from the most posterior teat pairs.

This behavior is justified by the dominance hierarchy; larger piglets typically win more teat

61 disputes (de Passillé and Rushen, 1989; Scheel et al., 1977), which allows them to secure ownership of preferred, anterior teats. However, birthweight and other factors measured only accounted for a minor amount of variation observed in teat selection during the first 24 hours of lactation, indicating that there are more substantial factors contributing to this behavior. Teat selection throughout lactation was most influenced by the teats selected during the first 24 hours of lactation. This is justified by previous data showing that teats preferentially nursed by piglets during the first week of lactation remain relatively consistent for the remainder of lactation (de

Passillé and Rushen, 1988; Špinka and Illmann, 2015).

Unexpectedly, piglets born with umbilical hematomas tended to nurse more posterior teat pairs throughout lactation. The present study is the first to observe this occurrence, and it may be related to hypoxia. Umbilical cord hematomas can indicate a piglet has been in the birth canal for too long and has experienced fetal distress from oxygen deprivation (Flowers, 2019).

Prenatal oxygen deprivation increases the risk of hypoxia and can result in less viable piglets

(Edwards and Baxter, 2015). Therefore, it is plausible that piglets born with umbilical hematomas had compromised viability which resulted in loss of teat competitions and consequent nursing of more posterior teats.

Differences in pre-weaning survival rates largely reflected losses that occurred within the first week of lactation. This agrees with previous observations that most pre-weaning mortality occurs within the first 72 hours of life (Edwards and Baxter, 2015). Consistent with data from

Lannom (2018) and Roehe and Kalm (2000), smaller birthweight piglets had reduced survival compared to their larger counterparts. These results were not surprising, as small piglets are often predisposed to hypothermia and pathogens due to low energy reserves and decreased consumption of colostrum (Edwards and Baxter, 2015). Also in agreement with Lannom (2018),

62 piglets that preferentially nursed more posterior teats had lower survival rates than piglets nursing more anterior teats. Expanding upon Lannom’s data, teat pairs nursed specifically during the first 24 hours of life significantly affected survival during the first week of lactation.

This is an important observation, as nursing location during the first 24 hours of lactation indicated which teats piglets suckled colostrum from. The associated results demonstrate that piglets suckling lower-quality colostrum from posterior teat pairs consequently had reduced chances of surviving the first week of lactation.

Surprisingly, piglets consistently nursing the same teat pair 51-80% of the time during lactation had greater pre-weaning survival than their counterparts with ≤ 50 and ≥ 81% nursing consistencies. Piglets with intermediate nursing consistency likely consumed a greater quantity of colostrum and milk through nursing other teats that were not initially emptied by their littermates. Previous data have shown that sampling more teat pairs during the colostral period is advantageous because it increases colostrum consumption (Špinka and Illmann, 2015).

Furthermore, it has been widely observed that smaller piglets do not suckle as much milk as larger piglets and cannot always empty their respective teats. Piglets with intermediate nursing consistency probably consumed more colostrum in early lactation, which gave them the proper nutrients to survive the early neonatal period. Once a teat order had been established, these piglets likely suckled from their preferential teats first and then sampled other teats for any remaining milk left by smaller piglets, ultimately consuming a greater quantity of nutrients to promote survival.

Providing an oral gavage of high-energy milk replacer to piglets within 24 hours after birth improved pre-weaning survival, most notably during the first week of lactation. This was the first study to examine the effectiveness of orally supplementing artificial milk shortly after

63 birth and provides new insight for effective neonatal management strategies. The results were not surprising, as piglet vigor, or activity level immediately after birth, has been shown to affect piglets’ nutritional intake. Piglets with low vigor typically win less teat disputes and consume less colostrum than their higher-energy counterparts (Baxter et al., 2008; Edwards and Baxter,

2015). Thus, supplemented piglets likely experienced a burst of energy which encouraged nursing and supplied piglets with the nutrients needed to survive the early neonatal period.

Previous research has observed higher stillbirth rates for piglets born in the last third of the birth order and in lengthier than average birth intervals (Baxter et al., 2008; van Dijk et al.,

2005), which is thought to be due to oxygen deprivation (Edwards and Baxter, 2015). However, the present study found no such effects on pre-weaning survival. While unexpected, these differences may be due to the extensive management of farrowing sows in the present study.

Because sows were consistently monitored and piglets were manually removed when necessary, the risk of hypoxia was likely reduced.

Piglet pre-weaning growth performance was largely influenced by birthweight and nursing behavior. In agreement with previous research (Quiniou et al., 2002; Smith et al., 2007), largest birthweight piglets consistently had superior growth performance compared to their lighter counterparts. This effect was likely due to greater milk consumption throughout lactation, as larger piglets consume more milk than smaller littermates during nursing bouts

(Martineau et al., 2012; Quesnel et al., 2015). In agreement with Lannom (2018), piglets that nursed anterior teat pairs had greater pre-weaning growth performance compared to their counterparts that nursed more posterior teats. These results reflect the variation in colostrum and milk quality across different teat pairs observed in the present study and by Lannom (2018).

Piglets that nursed more anterior teats received higher-quality colostrum and milk, which promoted their subsequent growth during lactation.

Interestingly, the presence of umbilical hematomas at birth impeded pre-weaning growth performance. The suggested mechanism for teat selection is also plausible here. Piglets with umbilical hematomas were at greater risk for hypoxia and likely born less vigorous than their littermates. Their reduced activity level after birth consequently put them lower in the dominance hierarchy, which hindered their ability to win teat disputes and timely nurse from productive teats. Therefore, these piglets likely consumed less colostrum and milk during lactation, which limited their subsequent growth performance.

As expected, providing supplemental milk to entire litters throughout lactation improved pre-weaning growth. This is consistent with data from Quesnel et al. (2015) which observed greater weight gain each week of lactation for litters supplemented with milk replacer. In the present study, access to supplemental milk was given when milk production by the sow was deemed suboptimal. Thus, piglets initially receiving inadequate nutrients from the sow had greater nutritional intake through ad libitum access to additional milk. Conversely, administering an oral gavage of milk replacer shortly after birth did not influence pre-weaning growth performance. This was also expected because treated piglets were only given one dosage of milk replacer, therefore it primarily served to increase energy during the early colostral period.

In conclusion, birthweight and nursing location critically influence pre-weaning success, as indicated by the reduced survival and growth observed for low birthweight piglets and piglets nursing posterior teat pairs. These effects were a direct result of the variation in nutritional quality across teat pairs. Future research and efforts aiming to prevent pre-weaning losses should concentrate on the first week of life, as this was the critical period for pre-weaning

65 survival. Providing supplemental milk shortly after birth may be a viable solution and should be further evaluated for its effects on disadvantaged piglets.

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Roehe, R. and Kalm, E., 2000. Estimation of genetic and environmental risk factors associated with pre-weaning mortality in piglets using generalized linear mixed models. Animal Science 70: 227-240. Scheel, D.E., Graves, H.B. and Sherritt, G.W., 1977. Nursing order, social dominance and growth in swine. Journal of Animal Science 45: 219-229.

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CONCLUSIONS While many perinatal factors influence a piglet’s success during the pre-weaning period, the present study identified which may be the most important determinants. As illustrated in

Figure 5, birthweight, nursing consistency, anatomical nursing location, and an oral gavage of artificial milk most significantly affected pre-weaning survival. Specifically, low birthweight piglets, piglets with the greatest nursing consistency, piglets nursing posterior teat pairs, and piglets not given an oral gavage of milk had reduced survival compared to their counterparts.

Pre-weaning growth was primarily impacted by birthweight, anatomical nursing location, and access to supplemental milk throughout lactation (Figure 5). As with survival, low birthweight piglets, piglets nursing posterior teat pairs, and piglets not given access to supplemental milk had reduced growth compared to their counterparts. This study provides further evidence of the complexity of pre-weaning success, as many of these factors are interconnected and related to piglet vigor. Low birthweight piglets, specifically weighing < 1.1 kg, are often associated with low vigor, which places them lower on the dominance hierarchy than their larger littermates, and consequently impedes their survival and growth. The presence of umbilical hematomas is also related to piglet vigor. Umbilical hematomas are associated with fetal distress and hypoxia, thus decreasing vigor. Anatomical nursing location, while largely not understood, is at least partially influenced by birthweight and vigor, with lower birthweight and less vigorous piglets suckling less productive, posterior teats. Colostrum quality directly relates to anatomical nursing location, as the reduced success of piglets nursing posterior teats can be explained by the decreased quality of colostrum from those teats. The effects of nursing consistency and administering an oral gavage of milk replacer can also be explained by colostrum consumption. Piglets with intermediate nursing consistency suckled from multiple teat pairs, likely consuming more colostrum and improving their chances of survival. Likewise, administering an oral gavage of

70 milk replacer improved survival, likely through increasing piglet vigor and resulting in greater colostrum consumption. Lastly, the effect of providing supplemental milk throughout lactation indirectly relates to piglet vigor, through the dominance hierarchy. Providing an additional source of milk alleviates the pressures of littermate competition, allowing piglets to consume greater quantities of nutrients to promote growth. Thus, more disadvantaged piglets have a greater chance of consuming enough milk to support proper growth.

In summary, the present study reveals that the most disadvantaged piglets may be piglets with birthweights < 1.1 kg, piglets suckling from posterior teats at any time during lactation, and piglets born with low vigor. Low birthweight piglets and piglets nursing from posterior teats consistently had reduced pre-weaning survival and growth. These characteristics, along with the presence of umbilical hematomas, are associated with low vigor, which consequently positioned piglets lower on the dominance hierarchy. The results of this study suggest that low birthweight piglets, piglets nursing posterior teats, and piglets with low vigor may benefit most from targeted neonatal management practices. Providing additional management to these piglets may significantly improve overall pre-weaning success.

TABLES Table 1. Effect of Teat Location and Time Relative to Farrowing on Dry Matter (%) in Colostruma

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansb

0 27.4 + 0.6x 19.3 + 0.5w 23.3 + 0.9 (8) (8)

24 22.2 + 0.3y 17.0 + 0.2z 19.6 + 0.5 (8) (8)

Teat Location Meansc 24.8 + 0.6 18.2 + 0.3 a interaction between time and teat location (p = 0.0036) b main effect of time (p < 0.0001) c main effect of teat location (p < 0.0001) x,y means within the same column with different superscripts differ (p < 0.0001) w,z means within the same column with different superscripts differ (p = 0.001)

Table 2. Effect of Teat Location and Time Relative to Farrowing on Fat (%) in Colostrum

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansa

0 7.6 + 0.4 7.7 + 0.4 7.7 + 0.3 (8) (8)

24 6.5 + 0.4 5.8 + 0.5 6.2 + 0.3 (8) (8)

Teat Location Meansb 7.0 + 0.3 6.7 + 0.3 a main effect of time (p = 0.001) b no main effect of teat location (p = 0.5059)

Table 3. Effect of Teat Location and Time Relative to Farrowing on Protein (%) in Colostruma

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansb

0 17.9 + 0.3x 5.8 + 0.3 11.8 + 1.2 (8) (8)

24 15.3 + 0.2y 5.3 + 0.3 10.3 + 1.0 (8) (8)

Teat Location Meansc 16.6 + 0.3 5.5 + 0.2 a interaction between time and teat location (p = 0.0015) b main effect of time (p < 0.0001) c main effect of teat location (p < 0.0001) x,y means within the same column with different superscripts differ (p < 0.0001)

Table 4. Effect of Teat Location and Time Relative to Farrowing on Lactose (%) in Colostrum

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansa

0 5.5 + 0.2 2.5 + 0.2 4.0 + 0.3 (8) (8)

24 5.1 + 0.3 2.5 + 0.2 3.8 + 0.3 (8) (8)

Teat Location Meansb 5.3 + 0.2 2.5 + 0.2 a no main effect of time (p = 0.4268) b main effect of teat location (p < 0.0001)

Table 5. Effect of Teat Location and Time Relative to Farrowing on Ash (%) in Colostruma

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansb

0 0.87 + 0.03 0.55 + 0.04x 0.71 + 0.04 (8) (8)

24 0.80 + 0.03 0.65 + 0.02y 0.72 + 0.02 (8) (8)

Teat Location Meansc 0.81 + 0.02 0.60 + 0.02 a interaction between time and teat location (p = 0.0133) b no main effect of time (p = 0.6072) c main effect of teat location (p < 0.0001) x,y means within the same column with different superscripts differ (p =0.0249)

Table 6. Effect of Teat Location and Time Relative to Farrowing on IgG Content (mg/mL) of Colostruma

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansb

0 76.0 + 4.2x 59.5 + 1.6w 67.8 + 2.8 (8) (8)

24 18.8 + 1.5y 13.0 + 1.1z 15.9 + 1.1 (8) (8)

Teat Location Meansc 47.4 + 6.3 36.2 + 4.9 a interaction between time and teat location (p = 0.0427) b main effect of time (p < 0.0001) c main effect of teat location (p < 0.0001) x,y means within the same column with different superscripts differ (p < 0.0001) w,z means within the same column with different superscripts differ (p = 0.001)

Table 7. Effect of Teat Location and Time Relative to Farrowing on IgA Content (mg/mL) of Colostrum

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansa

0 12.9 + 0.4 12.7 + 0.3 12.8 + 0.2 (8) (8)

24 4.2 + 0.6 4.2 + 0.5 4.2 + 0.3 (8) (8)

Teat Location Meansb 8.7 + 0.9 8.6 + 0.9 a main effect of time (p < 0.0001) b no main effect of teat location (p = 0.8571)

Table 8. Effect of Teat Location and Time Relative to Farrowing on IgM Content (mg/mL) of Colostrum

Teat Location

Time Relative to Farrowing (hours) First Two Pairs Last Two Pairs Time Meansa

0 6.6 + 0.4 6.0 + 0.5 6.3 + 0.3 (8) (8)

24 2.0 + 0.3 2.1 + 0.2 2.0 + 0.2 (8) (8)

Teat Location Meansb 4.6 + 0.5 4.3 + 0.5 a main effect of time (p < 0.0001) b no main effect of teat location (p = 0.6543)

Table 9. Multiple Regression Analyses for First Pair of Teats Nursed by Piglets1,2

Production Variable Partial R-Square Model R-Square Pr > F

Birthweight (kg) 0.0134 0.0134 0.0021

Total number born in litter 0.0053 0.0187 0.0520

Birth order 0.0050 0.0237 0.0589

Sow parity 0.0049 0.0286 0.0630

1variables eligible to enter model included the following: piglet birth order; piglet birth weight; interval from onset of farrowing to piglet birth; length of parturition; presence of meconium on piglets at birth; presence of umbilical cord hematomas at birth; whether piglet was delivered manually; and total number born in litter. 2variables entered model at p < 0.15.

Table 10. Effect of Birthweight on Anatomical Location of Teats Nursed by Piglets During the First 24 Hours After Birth (% of piglets nursing + s.e.m).1

Anatomical Location of Teats

Birthweight Category2,3,4 Pairs 1 and 2 Pairs 3 through 6 Pairs 7 and 8

< 1.09 kg / 0.92 + 0.01 kg 20.6 + 4.7x 15.2 + 3.8x 64.1 + 4.6x (92)

1.10 - 1.80 kg / 1.48 + 0.01 kg 33.7 + 3.8y 41.2 + 4.2y 25.1 + 3.9y (495)

> 1.80 kg / 1.96 + 0.01 kg 40.9 + 4.6y 42.7 + 5.3y 16.4 + 4.5y (122)

1proportion of piglets within each birthweight category based on nursing activity of 61 litters 2birthweight category and corresponding mean (+ s.e.m.) birthweight 3birthweight categories based on overall population mean + 1 standard deviation 4numbers in parenthesis are total number of pigs in each birthweight category x,ymeans with different superscripts in the same column are different (p < 0.05)

Table 11. Multiple Regression Analyses for Pair of Teats Nursed Most Often by Piglets1,2

Production Variable Partial R-Square Model R-Square Pr > F

Anatomical location of teats nursed 0.9829 0.9829 < 0.0001 during first 24 hours of lactation

Umbilical Hematoma 0.0001 0.9830 0.0929

1variables eligible to enter model included the following: piglet birth order; piglet birthweight; interval from onset of farrowing to piglet birth; length of parturition; presence of meconium on piglets at birth; presence of umbilical cord hematomas at birth; whether piglet was delivered manually; and total number born in litter. 2variables entered model at p < 0.15.

Table 12. Main Effects of Selected Production Variables on Piglet Survival (%) During Lactation

Piglet Survival (%) Day 0 to 7 Day 8 to 15 Day 16 to 21 Day 0 to 21 Production Variables of lactation of lactation of lactation of lactation

Sow parity 0.1894 0.0498 0.1441 0.4291

Total pigs born in litter 0.5846 0.6967 0.4632 0.9006

Birth order of piglet 0.5055 0.3072 0.9022 0.4872

Time piglet remained in birth 0.7574 0.7579 0.9049 0.4456 canal relative to first piglet born

Length of parturition 0.2107 0.3636 0.9743 0.2480

Manual assistance provided 0.8942 0.1606 0.6924 0.2287

Umbilical hematoma 0.2491 0.4045 0.9781 0.1415

Meconium present 0.1529 0.9816 0.9891 0.5808

Birth weight 0.0001 0.1557 0.0095 < 0.0001

First pair of teats nursed after 0.0432 0.9734 0.9830 0.0497 birth

Oral gavage of milk replacer 0.0325 0.2807 0.6943 0.0429

Number of piglets in nursing in 0.3820 0.0922 0.7623 0.1562 litter after cross-fostering

Pair of teats nursed most 0.0496 0.4446 0.2771 0.0473 during lactation

Nursing consistency1 < 0.0001 < 0.0001 0.1039 < 0.0001

Supplemental milk source for 0.2584 0.9146 0.1671 0.5971 entire litter

Number piglets weaned 0.0142 0.0011 0.2349 < 0.0001

1nursing consistency was defined as the percentage of nursing bouts during which piglets nursed the same pair of teats during each observation period during lactation.

Table 13. Effect of Birthweight on Piglet Survival (mean + s.e.m.) During Lactation1.

Piglet Survival (%)

Day 0 to 7 Day 8 to 15 Day 16 to 21 Day 0 to 21 Birthweight Category2,3 of lactation4 of lactation5 of lactation6 of lactation7

< 1.09 kg / 0.92 + 0.01 kg 69.1 + 4.7x 85.9 + 4.1 88.5 + 4.1x 57.4 + 5.1x (94) (71) (61) (94)

1.10 - 1.80 kg / 1.48 + 0.01 kg 90.1 + 1.3y 93.4 + 1.1 96.9 + 0.8y 83.3 + 1.6y (498) (457) (428) (498)

> 1.80 kg / 1.96 + 0.01 kg 95.9 + 1.8z 96.6 + 1.6 100.0 94.2 + 2.1z (122) (115) (115) (122)

1numbers in parentheses are number observations for each mean 2birthweight category and corresponding mean (+ s.e.m.) birthweight 3birthweight categories based on overall population mean + 1 standard deviation 4main effect of birthweight (p = 0.0001) 5no effect of birthweight (p = 0.1557) 6main effect of birthweight (p = 0.0095) 7main effect of birthweight (p < 0.0001) x,y,zmeans within the same column with different superscripts are different (p < 0.05)

Table 14. Effect of Anatomical Location of Teats Nursed During the First 24 Hours After Farrowing on Piglet Survival (mean + s.e.m.) During Lactation1

Piglet Survival (%)

Day 0 to 7 Day 8 to 15 Day 16 to 21 Day 0 to 21 Anatomical Location2,3 of lactation4 of lactation5 of lactation6 of lactation7

Pair 1 / 81.2 + 2.0% 89.3 + 2.6x,y 94.2 + 2.1 99.1 + 0.8 85.6 + 3.0x (132) (121) (114) (132)

Pair 2 / 73.3 + 2.0% 89.7 + 2.8x,y 93.8 + 2.2 97.1 + 1.6 83.0 + 3.3x (124) (113) (106) (124)

Pair 3 / 68.5 + 1.8% 89.1 + 2.8x,y 89.2 + 2.9 96.0 + 1.9 80.8 + 3.6x (120) (112) (101) (120)

Pair 4 / 69.3 + 2.1% 85.7 + 3.6x,z 97.4 + 1.8 98.6 + 1.3 82.4 + 4.0x (91) (78) (76) (91)

Pair 5 / 65.3 + 2.2% 93.1 + 2.7y 96.3 + 2.0 93.6 + 2.7 84.0 + 3.9x (88) (82) (79) (88)

Pair 6 / 72.3 + 2.2% 90.2 + 3.2x,y 92.2 + 3.0 95.7 + 2.4 82.9 + 4.1x (82) (77) (71) (82)

Pairs 7 & 8 / 72.5 + 2.7% 80.5 + 4.5z 89.0 + 3.9 94.7 + 2.9 70.1 + 5.2y (77) (64) (57) (77)

1numbers in parentheses are number observations for each mean 2anatomical location was assigned beginning with most anterior pair of teats 3mean nursing consistency (+ s.e.m.) for each pair of teats 4main effect of teats nursed during the first 24 hours after farrowing (p = 0.0432) 5no effect of teats nursed during the first 24 hours after farrowing (p = 0.9734) 6no effect of teats nursed during the first 24 hours after farrowing (p = 0.9830) 7main effect of teats nursed during the first 24 hours after farrowing (p = 0.0497) x,y,zmeans within the same column with different superscripts are different (p < 0.05)

Table 15. Effect of Anatomical Location of Teats Nursed During Lactation on Piglet Survival (mean + s.e.m.)1

Piglet Survival (%)

Day 0 to 7 Day 8 to 15 Day 16 to 21 Day 0 to 21 Anatomical Location2,3 of lactation4 of lactation5 of lactation6 of lactation7

Pair 1 / 82.9 + 1.9% 89.3 + 2.7x,y 94.1 + 2.1 99.1 + 0.8 86.3 + 3.0x (131) (120) (114) (131)

Pair 2 / 72.7 + 2.0% 89.2 + 2.8x,y 93.9 + 2.2 96.3 + 1.8 82.0 + 3.4x (128) (116) (109) (128)

Pair 3 / 69.2 + 1.7% 90.4 + 2.6x,y 89.8 + 2.7 97.1 + 1.6 83.2 + 3.3x (125) (118) (101) (125)

Pair 4 / 68.5 + 2.1% 84.6 + 3.8x,z 97.4 + 1.8 97.3 + 1.3 80.2 + 4.1x (91) (77) (75) (91)

Pair 5 / 62.5 + 2.2% 93.3 + 2.6y 96.4 + 2.0 93.8 + 2.6 84.4 + 3.8x (90) (84) (81) (90)

Pair 6 / 71.8 + 2.4% 90.6 + 3.3x,y 91.5 + 3.3 98.4 + 1.5 85.3 + 4.1x (75) (71) (65) (75)

Pairs 7 & 8 / 75.1 + 2.7% 80.5 + 4.6z 90.0 + 3.9 90.7 + 3.9 68.0 + 5.5y (72) (60) (54) (72)

1numbers in parentheses are number observations for each mean 2anatomical location was assigned beginning with most anterior pair of teats 3mean nursing consistency (+ s.e.m.) for each pair of teats 4main effect of anatomical location of teats nursed during lactation (p = 0.0496) 5no effect of anatomical location of teats nursed during lactation (p = 0.4446) 6no effect of anatomical location of teats nursed during lactation (p = 0.2771) 7main effect of anatomical location of teats nursed during lactation (p = 0.0473) x,y,zmeans within the same column with different superscripts are different (p < 0.05)

Table 16. Effect of Nursing Consistency on Piglet Survival (mean + s.e.m.) During Lactation1

Piglet Survival (%)

Day 0 to 7 Day 8 to 15 Day 16 to 21 Day 0 to 21 Nursing Consistency Category2,3 of lactation4 of lactation5 of lactation6 of lactation7

< 50% / 47.2 + 0.48% 98.0 + 0.8x 94.9 + 1.3x 96.3 + 1.2 90.0 + 1.8x (262) (258) (245) (262)

51 - 80% / 73.9 + 0.21% 100.0 99.1 + 0.6y 96.0 + 1.2 95.6 + 1.3y (231) (230) (229) (231)

> 81% / 99.6 + 0.13% 64.7 + 3.2y 81.6 + 3.0z 98.4 + 1.0 57.4 + 3.3z (221) (158) (129) (221)

1numbers in parentheses are number observations for each mean 2nursing consistency was defined as the percentage of nursing bouts during which piglets nursed the same pair of teats during lactation and were based on the upper, middle, and lower one-third of the population. 3nursing consistency category and corresponding mean nursing consistency (+ s.e.m.) 4main effect of nursing consistency (p < 0.0001) 5main effect of nursing consistency (p < 0.0001) 6no effect of nursing consistency (p = 0.1039) 7main effect of nursing consistency (p < 0.0001) x,y,zmeans within the same column with different superscripts are different (p < 0.05)

Table 17. Effect of Oral Gavage of Supplemental Milk During the First 24 Hours of Life on Piglet Survival (mean + s.e.m.) During Lactation1

Piglet Survival (%)

Day 0 to 7 Day 8 to 15 Day 16 to 21 Day 0 to 21 Treatment of lactation2 of lactation3 of lactation4 of lactation5

No milk replacer within 85.4 + 1.4x 92.8 + 1.2 96.4 + 0.8 78.5 + 1.7x 24 h of birth (205) (175) (169) (161)

Milk replacer gavage within 90.7 + 1.9y 94.1 + 1.7 97.1 + 1.2 84.8 + 2.0y 24 h of birth (204) (187) (176) (173)

1numbers in parentheses are number observations for each mean 2main effect of oral gavage (p = 0.0325) 3no effect of oral gavage (p = 0.2807) 4no effect of oral gavage (p = 0.6943) 5main effect of oral gavage (p = 0.0429)

Table 18. Effect of Birth Interval on Piglet Survival (mean + s.e.m.) During Lactation1,2

Piglet Survival (%)

Day 0 to 7 Day 8 to 15 Day 16 to 21 Day 0 to 21 Birth Interval Category3,4 of lactation of lactation of lactation of lactation

< 16 min / 3.2 + 0.4 min 86.8 + 3.0 91.7 + 2.6 95.0 + 2.1 77.8 + 3.7 (122) (109) (100) (122)

17 - 192 min / 94.2 + 2.0 min 88.3 + 1.4 93.3 + 1.1 96.6 + 0.8 82.1 + 1.7 (499) (453) (424) (499)

> 192 min / 273.8 + 7.8 min 90.3 + 3.0 94.1 + 2.5 98.7 + 1.2 84.9 + 3.7 (93) (95) (80) (93)

1numbers in parentheses are number observations for each mean 2no effect of birth interval on piglet survival was observed (p > 0.4456) 3birth interval category and corresponding mean birth interval (+ s.e.m.) 4birth interval was defined as the length of time relative to the first pig born which was assigned a value of 0 minutes and birth interval categories are based on overall population mean + 1 standard deviation

Table 19. Multiple Regression Analyses for Weight Gain (kg) During the First Week of Lactation1,2

Production Variable Partial R-Square Model R-Square Pr > F

Birthweight (kg) 0.1585 0.1585 < 0.0001

Anatomical location of teats nursed 0.0607 0.2192 < 0.0001 most often during lactation

Total number born per litter 0.0267 0.2459 < 0.0001

Sow parity 0.0092 0.2551 0.0061

Length of parturition 0.0057 0.2608 0.0294

Anatomical location of teats nursed 0.0034 0.2642 0.0941 during first 24 hours of lactation

1variables eligible to enter model included the following: sow parity; total number of pigs born; length of farrowing; birth order of piglets; interval from onset of farrowing to piglet birth; presence of meconium on piglets at birth; presence of umbilical cord hematomas at birth; whether the piglet was manually removed during farrowing; birthweight; first pair of teats piglets nursed immediately after birth; whether piglets were given an oral gavage of supplemental milk during the first 24 h after birth; pair of teats nursed most frequently during entire lactation; nursing consistency; total number of pigs nursing; whether supplemental milk was provided for the entire litter after the first week of lactation; and number of pigs weaned 2variables entered model at p < 0.15

Table 20. Multiple Regression Analyses for Pre-Weaning Weight Gain (kg)1,2

Production Variable Partial R-Square Model R-Square Pr > F

Birthweight (kg) 0.1673 0.1673 < 0.0001

Anatomical location of teats nursed 0.0862 0.2535 < 0.0001 most often during lactation

Total number born per litter 0.0287 0.2822 < 0.0001

Access to supplemental milk 0.0235 0.3057 < 0.0001

Umbilical hematoma 0.0085 0.3142 0.0079

Length of parturition 0.0032 0.3174 0.1037

Anatomical location of teats nursed 0.0028 0.3202 0.1276 during first 24 hours of lactation

Table 21. Multiple Regression Analyses for Weaning Weight (kg)1,2

Production Variable Partial R-Square Model R-Square Pr > F

Birthweight (kg) 0.3328 0.3328 < 0.0001

Anatomical location of teats nursed 0.0688 0.4016 < 0.0001 most often during lactation

Total number born per litter 0.0229 0.4245 < 0.0001

Access to supplemental milk 0.0188 0.4433 < 0.0001

Umbilical hematoma 0.0068 0.4501 0.0079

Length of parturition 0.0025 0.4526 0.1037

Anatomical location of teats nursed 0.0022 0.4548 0.1276 during first 24 hours of lactation

Table 22. Effect of Birthweight on Piglet Pre-Weaning Growth Characteristics (mean + s.e.m.) During Lactation1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Birthweight Category2,3 and 7 of lactation4 and 21 of lactation5 Weight6

< 1.09 kg / 0.92 + 0.01 kg 0.75 + 0.05x 3.57 + 0.14x 4.53 + 0.14x (65) (54) (54)

1.10 - 1.80 kg / 1.48 + 0.01 kg 1.14 + 0.02y 4.85 + 0.06y 6.35 + 0.06y (448) (415) (415)

> 1.80 kg / 1.96 + 0.01 kg 1.43 + 0.04z 5.56 + 0.11z 7.51 + 0.11z (117) (115) (115)

1numbers in parentheses are number observations for each mean 2birthweight category and corresponding mean (+ s.e.m.) birthweight 3birthweight categories based on overall population mean + 1 standard deviation 4main effect of birthweight (p < 0.0001) 5main effect of birthweight (p < 0.0001) 6main effect of birthweight (p < 0.0001) x,y,zmeans with different superscripts in the same column are different (p < 0.05)

Table 23. Effect of Anatomical Location of Teats Nursed During Lactation on Pre-Weaning Growth Characteristics of Piglets (mean + s.e.m.)1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Anatomical Location2,3 and 7 of lactation4 and 21 of lactation5 Weight6

Pair 1 / 81.2 + 2.0% 1.39 + 0.04w 5.42 + 0.13w 7.00 + 0.14w (117) (113) (113)

Pair 2 / 73.3 + 2.0% 1.23 + 0.04x 5.11 + 0.11x 6.68 + 0.13x (113) (105) (105)

Pair 3 / 68.5 + 1.8% 1.16 + 0.04x 5.08 + 0.11x 6.64 + 0.13x (113) (104) (104)

Pair 4 / 69.3 + 2.1% 1.16 + 0.05x 4.89 + 0.15x 6.46 + 0.19x (77) (73) (73)

Pair 5 / 65.3 + 2.2% 1.01 + 0.04y 4.50 + 0.13y 5.98 + 0.16y (84) (76) (76)

Pair 6 / 72.3 + 2.2% 1.00 + 0.05y 4.38 + 0.13y 5.90 + 0.15y (68) (64) (64)

Pairs 7 & 8 / 72.5 + 2.7% 0.89 + 0.06y 3.82 + 0.17z 5.22 + 0.19z (58) (54) (54)

1numbers in parentheses are number observations for each mean 2anatomical location was assigned beginning with most anterior pair of teats 3mean nursing consistency (+ s.e.m.) for each pair of teats 4main effect of anatomical location of teats nursed during lactation (p < 0.0001) 5main effect of anatomical location of teats nursed during lactation (p < 0.0001) 6main effect of anatomical location of teats nursed during lactation (p < 0.0001) w,x,y,zmeans with different superscripts within the same column are different (p < 0.05)

Table 24. Effect of Anatomical Location of Teats Nursed During the First 24 Hours After Farrowing on Pre-Weaning Growth Characteristics of Piglets (mean ± s.e.m.) During Lactation1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Anatomical Location2,3 and 7 of lactation4 and 21 of lactation5 Weight6

Pair 1 / 81.2 + 2.0% 1.31 + 0.05w 5.19 + 0.13 6.77 + 0.14 (118) (113) (113)

Pair 2 / 73.3 + 2.0% 1.21 + 0.05w,x 5.03 + 0.12 6.55 + 0.14 (110) (103) (103)

Pair 3 / 68.5 + 1.8% 1.17 + 0.04x,y 5.13 + 0.13 6.70 + 0.15 (107) (97) (97)

Pair 4 / 69.3 + 2.1% 1.10 + 0.05y,z 4.73 + 0.14 6.25 + 0.16 (78) (75) (75)

Pair 5 / 65.3 + 2.2% 1.03 + 0.05z 4.59 + 0.14 6.10 + 0.16 (82) (74) (74)

Pair 6 / 72.3 + 2.2% 1.07 + 0.05y.z 4.56 + 0.14 6.06 + 0.16 (74) (68) (68)

Pairs 7 & 8 / 72.5 + 2.7% 1.07 + 0.05y,z 4.43 + 0.16 5.09 + 0.18 (61) (54) (54)

1numbers in parentheses are number observations for each mean 2anatomical location was assigned beginning with most anterior pair of teats 3mean nursing consistency (+ s.e.m.) for each pair of teats 4tendency of effect of teats nursed during the first 24 hours after farrowing (p = 0.0941) 5no effect of teats nursed during the first 24 hours after farrowing (p = 0.6129) 6no effect of teats nursed during the first 24 hours after farrowing (p = 0.6129) w,x,y,zmeans with different superscript in the same column tend to be different (p < 0.1)

Table 25. Pre-Weaning Growth Characteristics (mean + s.e.m.) of Piglets with Umbilical Hematomas at Farrowing1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Umbilicus Appearance and 7 of lactation2 and 21 of lactation3 Weight4

No umbilical hematoma 1.16 + 0.02 4.90 + 0.05 6.44 + 0.06 (597) (554) (554) Umbilical hematoma 1.02 + 0.09 4.30 + 0.22 5.84 + 0.26 (30) (30) (30)

1numbers in parentheses are number observations for each mean 2main effect of presence of umbilical hematoma (p = 0.0798) 3main effect of presence of umbilical hematoma (p = 0.0070) 4main effect of presence of umbilical hematoma (p = 0.0070)

Table 26. Effect of Providing Supplemental Milk During Lactation on Piglet Pre-Weaning Growth Characteristics (mean + s.e.m.)1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Treatment and 7 of lactation2 and 21 of lactation3 Weight4

No supplemental milk 1.09 + 0.02 4.49 + 0.06 5.96 + 0.07 (393) (372) (372) Supplemental milk 1.19 + 0.03 5.09 + 0.09 6.66 + 0.10 (237) (173) (173)

1numbers in parentheses are number observations for each mean 2no effect of supplemental milk (p = 0.1071) 3main effect of supplemental milk (p < 0.0001) 4no effect of supplemental milk (p < 0.0001)

Table 27. Effect of Sow Parity on Piglet Pre-Weaning Growth Characteristics (mean + s.e.m.) During Lactation1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Sow Parity Category2,3 and 7 of lactation4 and 21 of lactation5 Weight6

Parity 2 1.12 + 0.03x 4.87 + 0.16 6.47 + 0.17 (99) (96) (96)

Parities 3 - 6 / 4.3 + 0.1 1.18 + 0.02y 4.89 + 0.06 6.45 + 0.07 (345) (221) (221)

Parities > 7 / 8.8 + 0.1 1.16 + 0.03x,y 4.82 + 0.16 6.29 + 0.12 (186) (162) (162)

1numbers in parentheses are number observations for each mean 2parity groups based on typical differences in total number born and number born alive. 3sow parity group nd corresponding mean sow parity (+ s.e.m.) 4main effect of sow parity (p = 0.0061) 5no effect of sow parity (p = 0.4216) 6no effect of sow parity (p = 0.3412) x,ymeans with different superscripts in the same column are different (p < 0.05)

Table 28. Effect of Length of Parturition on Piglet Pre-Weaning Growth Characteristics (mean + s.e.m.) During Lactation1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Farrowing Length Category2,3 and 7 of lactation4 and 21 of lactation5 Weight6

< 180 min / 137.4 + 1.4 min 1.13 + 0.03 4.77 + 0.09x 6.38 + 0.09x,z (274) (251) (251)

180 - 360 min / 230.4 + 2.3 1.14 + 0.03 5.01 + 0.08y 6.57 + 0.09x,y min (259) (243) (243)

> 360 min / 423.3 + 7.1 min 1.24 + 0.04 4.78 + 0.12x 6.18 + 0.14z (97) (90) (90)

1numbers in parentheses are number observations for each mean 2parturition length categories and corresponding mean (+ s.e.m.) farrowing length 3parturition length categories are one third of the entire range observed between shortest (55 min) and longest (540 min) values 4no effect of parturition length (p = 0.2064) 5tendency for effect of parturition length (p = 0.0975) 6tendency for effect of parturition length (p = 0.0975) x,y,zmeans with different superscripts in the same column tend to be different (p < 0.1)

Table 29. Effect of Birth Interval on Piglet Pre-Weaning Growth Characteristics (mean + s.e.m.) During Lactation1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Birth Interval Category2,3 and 7 of lactation4 and 21 of lactation5 weight6

< 16 min / 3.2 + 0.4 min 1.14 + 0.04 4.57 + 0.16 6.10 + 0.17 (106) (95) (95)

17 - 192 min / 94.2 + 2.0 min 1.14 + 0.02 4.90 + 0.06 6.45 + 0.06 (441) (410) (410)

> 192 min / 273.8 + 7.8 min 1.22 + 0.05 5.06 + 0.15 6.55 + 0.18 (83) (79) (79)

1numbers in parentheses are number observations for each mean 2birth interval category and corresponding mean (+ s.e.m.) birth interval 3birth interval was defined as the length of time relative to the first pig born which was assigned a value of 0 minutes and birth interval categories are based on overall population mean + 1 standard deviation 4no effect of birth interval (p = 0.7975) 5no effect of birth interval (p = 0.1589) 6no effect of birth interval (p=0.1589)

Table 30. Effect of Nursing Consistency on Piglet Pre-Weaning Growth Characteristics (mean + s.e.m.) During Lactation1

Growth Performance (kg)

Weight change Weight change Nursing Consistency between days 0 between days 0 Weaning Category2,3 and 7 of lactation4 and 21 of lactation5 Weight6

< 50% / 47.2 + 0.48% 1.14 + 0.03 4.84 + 0.08 6.39 + 0.09 (261) (236) (236)

51 - 80% / 73.9 + 0.21% 1.12 + 0.03 4.78 + 0.09 6.32 + 0.10 (231) (221) (221)

> 81% / 99.6 + 0.13% 1.23 + 0.04 5.07 + 0.11 6.59 + 0.12 (142) (127) (127)

1numbers in parentheses are number observations for each mean 2nursing consistency was defined as the percentage of nursing bouts during which piglets nursed the same pair of nipples during lactation and were based on the upper, middle, and lower one- third of the population. 3nursing consistency category and corresponding mean nursing consistency (+ s.e.m.) 4no effect of nursing consistency (p = 0.1772) 5no effect of nursing consistency (p = 0.2669) 6no effect of nursing consistency (p = 0.2669)

Table 31. Effect of Oral Gavage of Supplemental Milk During the First 24 Hours of Life on Piglet Pre-Weaning Growth Characteristics (mean + s.e.m.) During Lactation1

Growth Performance (kg)

Weight change Weight change between days 0 between days 0 Weaning Treatment and 7 of lactation2 and 21 of lactation3 Weight4

No milk replacer within 1.15 + 0.04 4.89 + 0.10 6.43 + 0.11 24 h of birth (175) (161) (161)

Milk replacer gavage within 1.17 + 0.04 4.88 + 0.10 6.48 + 0.11 24 h of birth (187) (173) (173)

1numbers in parentheses are number observations for each mean 2no effect of oral gavage (p = 0.2070) 3no effect of oral gavage (p = 0.7484) 4no effect of oral gavage (p = 0.7484)

FIGURES

Figure 1. Unique combination of colored zip-ties applied to piglets’ tails.

Figure 2. Piglet covered with meconium.

Figure 3. Normal umbilical cord (top) compared to umbilical cord with hematomas (bottom).

Figure 4. Piglets nursing with different-colored crayon marks.

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Figure 5. Summary of perinatal factors affecting piglet pre-weaning success.

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APPENDICES

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Appendix A

Appendix A. Descriptive Statistics for Perinatal Variables Descriptive Statistics Perinatal Standard Standard Variable N Mean Deviation Error Minimum Maximum Sow parity1 61 5.1 2.8 0.3 2 15 Length of parturition (min)1 61 222.8 107.9 13.8 55 570 Total born1 61 14.9 3.2 0.4 5 20 Number born alive1 61 13.3 2.7 0.3 5 18 Number nursing after cross- 61 12.7 1.7 0.2 8 17 fostering1 Number weaned1 61 10.1 1.7 0.2 6 14 Farrowing interval (min)2,3 789 103.3 87.7 3.3 0 538 Birthweight (kg)2 709 1.49 0.33 0.01 0.44 2.58 Nipple pair nursed on day 1 709 3.6 1.9 0.1 1 7 of lactation2,4 Nipple pair nursed on day 8 623 3.6 1.9 0.1 1 7 of lactation2,4 Nipple pair nursed on day 597 3.6 1.9 0.1 1 7 15 of lactation2,4 Nipple pair nursed on day 581 3.5 1.9 0.1 1 7 21 of lactation2,4 Nursing consistency2,5 709 72.3 22.3 0.8 10 100 Piglets removed manually 789 36.3 ------during parturition (%)2,6 Piglets with meconium after 789 2.1 ------birth (%)2,6 Piglets with umbilical 789 5.5 ------hematomas after birth (%)2,6 Piglets with access to milk 789 36.0 ------replacer after day 7 (%)2,6 1litter variables 2piglet variables 3birth interval was defined as the length of time relative to the first pig born which was assigned a value of 0 minutes and birth interval categories are based on overall population mean + 1 standard deviation 4nipple pairs numbered consecutively 1 through 7 beginning with pair closest to the front legs. Pair 7 represents pairs 7 and 8 combined. 5nursing consistency was defined as the percentage of nursing bouts during which piglets nursed the same pair of teats during lactation and were based on the upper, middle, and lower one-third of the population. 6proportion of piglets meeting stated criterion

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Appendix B

Appendix B. Composition of Milk Replacer and Estimated Intake of Selected Nutrients

GUARANTEED ANALYSIS (From Feed Tag)

Crude Protein, minimum 20.00% Crude Fat, minimum 20.00% Crude Fiber, maximum 0.75% Calcium, minimum 1.25% Phosphorus, minimum 0.70% Vitamin A, minimum 30,000 IU/lb Vitamin D, minimum 10,000 IU/lb Vitamin E, minimum 100 IU/lb

INGREDIENT STATEMENT (From Feed Tag)

Dried whey, animal fat (preserved with BHA, BHT & citric acid), dried whey product, protein modified soy flour, soy flour, dried whey protein concentrate, calcium carbonate, L-lysine, lecithin, xanthan gum, DL-methionine, sodium silico aluminate, ferrous sulfate, ethoxylated mono-diglycerides, propylene glycol, magnesium sulfate, dried skim milk, choline chloride, vitaman E supplement, artificial flavor, maltodextrin, vitamin A supplement, magnesium sulfate, zinc sulfate, selenium yeast, brewer’s dried yeast, dicalcium phosphate, vitamin D3 supplement, copper sulfate, ascorbic acid, niacin supplement, calcium pantothenate, riboflavin supplement, vitamin B12 supplement, menadione sodium bisulfite complex (source of vitamin K activity), pyridoxine hydrochloride, thiamine mononitrate, biotin, calcium iodate, folic acid, cobalt sulfate.

Estimated Intake of Selected Nutrients in Oral Gavage (1 mL)

Crude Protein, minimum 10 grams Crude Fat, minimum 10 grams Calcium, minimum 375 milligrams Phosphorus, minimum 625 milligrams Vitamin A, minimum 3,303 IU Vitamin D, minimum 1,101 IU Vitamin E, minimum 11 IU

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