Factors Affecting Goat Milk Production and Quality

Small Ruminant Research 101 (2011) 55–63

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Small Ruminant Research

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Review article

ଝ

Factors affecting goat milk production and quality

∗

A.L. Goetsch , S.S. Zeng, T.A. Gipson

American Institute for Goat Research, Langston University, P. O. Box 1730, Langston, OK 73050, USA

a r t i c l e i n f o a b s t r a c t

Article history: Differences between production systems based on grazing and browsing vs. use of har-

Available online 5 October 2011

vested feedstuffs in conﬁnement largely depend on speciﬁc feedstuffs and plants available

and being consumed. Low forage nutrient ingestion should have relatively greater impact

Keywords:

on tissue mobilization than milk production in early than later periods of lactation, with a

Goats

transition to proportionally greater change in milk production in late lactation. However,

Milk

low body condition at kidding would limit tissue energy mobilization and restrict impact

Lactation

of level of nutrient intake to milk yield and, likewise, tissue mobilization would be less

with one vs. two or three milkings per day. As lactation advances after freshening, fat and

protein levels decrease with increasing milk yield, and when production declines in mid- to

late lactation, fat and protein concentrations increase. Milk production generally peaks at a

parity of 3 or 4, thereafter declining slowly. Elevated somatic cell count alone in dairy goats

is not a valid indication of mammary infection. Extended lactations offer opportunities to

minimize or avoid seasonal ﬂuctuations in milk production and lessen production costs. If

differences in performance between suckled and machine-milked dairy goats occur, they

may be restricted to or of greater magnitude during the suckling period compared with

post-weaning, and differences in milk yield will either be absent or less with one kid com-

pared with greater litter sizes. The magnitude of effects of milking frequency on milk yield

is less for goats of low vs. high production potential and with low vs. high diet quality.

Likewise, the effect of milking frequency is greater in early and mid-lactation when yield

is higher than in late lactation, along with a shorter period of peak production with one

vs. two daily milkings. Physical form of the diet can affect production and composition of

goat milk, although effects appear of smaller magnitude than in dairy cattle. When tissue

is mobilized to support milk production in early lactation, levels of C18:0 and C18:1 cis in

milk increase and levels of medium-chain fatty acids decline. Effects of elevated levels of

dietary fatty acids on speciﬁc long-chain fatty acids in milk and milk products vary with

the fatty acid proﬁle of fat sources used.

1. Introduction one particular setting may not always apply to others. Goats

of dairy breeds highly selected for milk production receive

There are many types of goats raised under quite varied more research consideration regarding milk yield and qual-

production conditions throughout the world. Findings in ity. However, the physiological state of lactation is also

integral to the rearing of all other genotypes and impor-

tant to food and economic securities of millions of people.

ଝ Therefore, this research summary is not restricted to dairy

This paper is part of the special issue entitled Products from Small

goat genotypes. Hence, in many locations in the manuscript

Ruminants, Guest Edited by A. Govaris and G. Moatsou.

∗ some information about goat genotype and production

Corresponding author. Tel.: +1 405 466 6164; fax: +1 405 466 6180.

E-mail address: [email protected] (A.L. Goetsch). conditions is included. The objective of this paper is to

56 A.L. Goetsch et al. / Small Ruminant Research 101 (2011) 55–63

provide an overview of some of the recent research regard- production started to decline, fat and protein concentra-

ing factors that inﬂuence the production and quality of goat tions again increased.

milk. Somatic cell count (SCC) in goat milk increases as lac-

tation advances. Gomes et al. (2006) reported that SCC

increased from 2.6 × 10 /ml in the ﬁrst month of lactation

2. Management practices and production 5

to 6.5 × 10 /ml in the eighth month. Paape et al. (2007)

systems/practices

found 2.5–4 times higher SCC in milk at 15 days in milk

(DIM) than at 285 DIM depending on parity. The extremely

2.1. Production systems

high SCC in milk at 15 DIM could have resulted from a

residual high SCC from colostrum because it was so close

Because diet affects the composition of goat milk and

to kidding. In bulk tank goat milk (n = 2582), elevated

milk products, differences between production systems

SCC was also observed in the latter months of lactation

based on grazing and browsing vs. use of harvested feed-

(August–December) (Zeng et al., 1999). Zeng et al. (2008)

stuffs in conﬁnement largely depend on speciﬁc feedstuffs

noted a trend for increasing SCC in the ﬁrst 8 months of lac-

and plants available and being consumed. As an example,

tation, with values relatively constant in the last 4 months.

Galina et al. (2007) observed many differences in the com-

Therefore, year-round breeding and lactation programs for

position of soft cheese made from milk of goats fed indoors

large herds would not only provide a constant supply of

compared with ones grazing rangeland with a diverse array

goat milk but would stabilize bulk tank SCC.

of plant species, although the diet of conﬁned animals was

Parity affects milk fat and protein concentrations, yield,

not reported. Soryal et al. (2004) noted a higher ﬂavor score

and SCC. Milk production is lower for primiparous than for

for Domiati cheese made from milk of Alpine goats graz-

multiparous dairy goats; highest production is for parity

ing without supplemental concentrate compared with ones

3 or 4 (Zeng and Escobar, 1995; Carnicella et al., 2008).

conﬁned and consuming a concentrate-alfalfa hay diet.

Similarly, Zahraddeen et al. (2009) found increasing par-

There are few reports available concerning effects of

tial daily milk yield as parity increased from 1 to 3 for Red

management practices such as stocking rate on milk pro-

Sokoto, Sahel, and West African Dwarf goats. Zeng et al.

duction by goats. With meat goat does grazing grass/forb

(2008) found that fat and protein concentrations were sim-

paddocks at low, moderate, and high stocking rates elic-

ilar among the ﬁrst ﬁve parities but were much less for

iting substantial differences in forage mass, average daily

parity 6. The SCC increases with increasing parity (Wilson

gain (ADG) by nursing twin kids was similar among

et al., 1995; Contreras et al., 1999; Salama et al., 2003;

stocking rates, but body weight (BW) of does decreased

Paape et al., 2007; Zeng et al., 2008). Milk of Saanen and

linearly as stocking rate increased, ranging from 36 to

− autochthonous Greek goats in parity 1 had the lowest SCC

82 g/day (Yiakoulaki et al., 2007). Conversely, Beker et al. 5

of 3.0 × 10 /ml and does in parity 6 had the highest SCC

(2009) noted similar BW change of meat goat does grazing 5

of 6.0 × 10 /ml (Boscos et al., 1996). The rise in SCC with

grass/forb pasture at low and high stocking rates, whereas

increasing parity relates to increasing bacterial presence

ADG by twin kid litters was lower for the high stocking

or cumulative mammary gland stress (Boscos et al., 1996).

rate. Similar variability in responses of dairy goat breeds to

Paape et al. (2007) concluded that much of the increase in

different levels of forage mass resulting from various man-

SCC is due to non-infectious factors, although increasing

agement practices is likely, with magnitudes of effects on

frequency of intra-mammary infections is also involved.

milk yield vs. tissue energy mobilization depending largely

Thus, culling goats after the ﬁfth lactation as their milk fat

on stage of lactation and initial body condition. That is,

and protein levels decrease and SCC rise may be beneﬁcial

low forage nutrient ingestion would have relatively greater

for meeting Grade “A” goat milk requirements.

impact on tissue mobilization than milk production in early

lactation, with a transition to proportionally greater change

2.3. Extended lactation

in milk production in late lactation (Ngwa et al., 2009;

Tovar-Luna et al., 2010a,b). However, low body condition at

Lactation length has an obvious effect on milk yield,

kidding would limit tissue mobilization and restrict impact

with greater quantities of milk and milk components for

to milk yield. Likewise, mobilization would be less with one

longer lactations. Watkin and Knowles (1946) noted that

vs. two or three milkings per day.

goats were able to lactate continuously for 24 months. In

another study, the French dairy goat industry evaluated

2.2. Stage of lactation, season, parity, and photoperiod extended lactations of 18 months as a means to ease the

seasonal restriction in milk supply experienced in winter

In the US, most kidding occurs in March with drying off (Gendron and Reveau, 1995). The French study concluded

in November or December (Zeng et al., 2008). During 2007, that extended lactations had a positive effect on equal-

both fat and protein contents in goat milk in the US were izing milk production throughout the year, yet had no

very high in January (5.1 and 4.5%, respectively), probably adverse effect on reproduction. In another French study,

because of the combination of the extremely low num- Brice (2000) noted that the curves for extended lacta-

ber of goats on test (84 and 403 in January and February, tions of primiparous does had two distinct phases. The

respectively) and low milk production (2.8 kg/day). Milk ﬁrst phase, consisting of the ﬁrst 10 months of lactation,

production increased and peaked in April (3.6 kg/day). As exhibited a normal lactation curve. The second phase, con-

lactation advanced after freshening, fat and protein lev- sisting of the last 8 months of lactation, resembled a normal

els decreased, being lowest in June and July. When milk lactation curve of the subsequent lactation. Brice (2000)

A.L. Goetsch et al. / Small Ruminant Research 101 (2011) 55–63 57

also noted that even though the last phase was smaller good predictor of the response to transitioning to milking

in scale than the preceding lactation curve, does undergo- once daily in mid- or late lactation.

ing an extended lactation produced as much milk as does

undergoing two normal lactations. This was due to extra 3. Breeding and genetics

months in lactation. An aspect of extended lactations that

the French have completely examined is milk processing 3.1. Genotype

quality, concluding that extended lactations have no neg-

ative effects. Milk yield can be deﬁned mathematically as the area

Unlike dairy cattle, goats do not appear to need an invo- under the lactation curve, with many factors affecting the

lution (dry) period for the mammary gland for optimal milk shape and scale of the curve and, thus, overall yield (Gipson

production in the subsequent lactation. In a study involv- and Grossman, 1990). Genetic effects are manifested indi-

ing four goats (Fowler et al., 1991), one mammary gland vidually and collectively. Individual genetic effects can be

was milked continuously for 66 weeks and the other gland seen in the expected progeny differences that are cal-

was milked for 25 weeks, dried off for 23 weeks during culated annually by USDA-AIPL (Wiggans and Hubbard,

rebreeding and pregnancy, and then milked for 18 weeks. 2001). Collectively, genetic differences are seen as breed

In the last 18 weeks of lactation, the continuously milked differences, with the Swiss breeds (Alpine, Saanen, and

gland tended to have higher milk yield, greater parenchyma Toggenburg) yielding more than Nubians or LaManchas

weight, and a greater number of secretory cells. However, (Gipson and Grossman, 1987, 1989). In a Mexican study, a

mammary enzyme activities did not differ between the two genetic group consisting of 1/2 to 15/16 crosses of Alpine,

glands. Saanen, and Toggenburg × local Mexican goats had greater

values for maximum daily milk production, average daily

production, persistency, and total milk production than a

2.4. Suckling and milk frequency genetic group consisting of 1/2 to 15/16 crosses of Granad-

ina and Nubian × local Mexican goats (Montaldo et al.,

Goats differ from dairy cattle in the neuroendocrine 1997). Primary non-genetic or environmental factors inﬂu-

milk ejection reﬂex because of relatively greater capacity encing milk yield include herd-year, parity, and season of

for milk storage in the gland cistern (Silanikove et al., 2010), kidding. In Italy, the herd-year effect was the primary factor

which suggests relatively little potential for beneﬁt in milk inﬂuencing milk yield (Crepaldi et al., 1999). The herd-year

yield from natural suckling compared with machine milk- effect reﬂected the different and changing management

ing. However, differences in performance between suckled systems in dairy goat production in that country, such as

and machine-milked dairy goats have been observed that feeding and milking techniques.

vary considerably with experimental or production con- Montaldo et al. (2010) reported that genetic and envi-

ditions. If differences occur, they will be restricted to or ronmental correlations between ﬁrst-parity milk yield and

of greater magnitude during the suckling period compared ﬁrst kidding interval were positive (unfavorable) for Alpine,

with post-weaning, and differences in milk yield will either LaMancha, Saanen, and Toggenburg, which is similar to

be absent or less with one kid compared with greater litter relationships found in dairy cattle. Thus, low reproduc-

sizes (Peris et al., 1997; Delgado-Pertínez˜ et al., 2009a,b). tive performance can accompany high potential for milk

If milk yield is greater for dams suckled than machine- production, reﬂecting need for consideration of reproduc-

milked, concentrations of fat and protein will most likely tive performance in selection strategies (Montaldo et al.,

be lower (Delgado-Pertínez˜ et al., 2009a,b). 2010). However, smaller unadjusted phenotypic vs. envi-

Traditionally, goats have been milked twice daily, but ronmental correlations of Montaldo et al. (2010) indicate

there is growing interest in reducing labor cost by tran- that appropriate management practices can lessen impact

sitioning to once-a-day milking. The magnitude of effect of this unfavorable relationship in dairy goats.

of milking frequency on milk yield varies with numerous Zeng et al. (2008) analyzed an extensive data set of dairy

factors, one of which is breed, with less impact for goats goats enrolled in Dairy Herd Improvement program in the

of low vs. high production potential and low vs. high diet US. Milk of Nigerian Dwarf goats had the highest level of

quality; however, the reduction is generally in the range fat (6.4%), which was more than double that of Sable milk

of 20% when compared with milking twice daily (Komara (3.0%). Among the six major dairy breeds, milk of Nubian

et al., 2009). Likewise, the effect of milking frequency is was the highest in fat content while that of Toggenburg was

greater in early and mid-lactation when yield is greater the lowest. Nigerian Dwarf and Pygmy milk was highest in

than in late lactation (Silanikove et al., 2010), along with protein (4.4%). Sable goats had greatest milk production

a shorter period of peak production with one vs. two daily (3.9 kg/day) and Pygmy and Nigerian Dwarf goats had low-

milkings (Salama et al., 2003, 2004). Because of increas- est values. Milk production for the six major dairy breeds

ing cisternal capacity as parity increases, the difference in ranked from greatest to least Alpine, Sannen, Oberhasli, La

milk yield between milking once and twice daily decreases. Mancha, Toggenburg, and Nubian. These differences in milk

Salama et al. (2003) noted that Murciano-Granadina does production partially account for those in fat and protein

in the ﬁrst through third parities had a greater reduction concentrations because of the ‘concentration factor,’ with

than does of higher parities. A corresponding interaction differences among breeds in daily fat and protein yields

between parity and milking frequency in milk fat concen- less marked than those in levels. Therefore, fat and protein

tration was also observed. Although, Komara et al. (2009) yields for a speciﬁc volume of milk may be better param-

concluded that udder cisternal size did not appear to be a eters for price incentives than fat and protein contents,

58 A.L. Goetsch et al. / Small Ruminant Research 101 (2011) 55–63

particularly when milk is used for cheese manufacture, as body tissue mobilized to support milk production for high

it is the case for more than half of the goat milk worldwide kid ADG and that perhaps the history of Boer goat selection

(Pirisi et al., 2007). involving greatest attention to growth rate and body size

Signiﬁcant variation in SCC among breeds was noted included indirect positive effect on feed intake potential

by Zeng et al. (2008), with Toggenburg and Nubian being impacting need for mobilization of tissue to support milk

the highest (5.7× and 5.3 × 10 /ml, respectively). The mean production. In support, Tamir et al. (2004) noted greater

SCC of milk from Toggenburg and Nubian were still well milk yield determined by periodic machine-milking fol-

below the current regulatory limit of 1.5 10 /ml for Grade lowing oxytocin injection by crossbred Boer than Spanish

“A” goat milk in the US. Paape et al. (2007) studied the goat goats on a low plane of nutrition, with similar kid ADG.

breed effect for a 5-year period and also found the highest

× 5

SCC (6.5 10 /ml) in Toggenburg milk. A similar ﬁnding 4. Health

was reported for Alpine, Nubian, Saanen, and Toggenburg

goats in Taiwan (Sung et al., 1999). The SCC in Toggenburg 4.1. Hygiene

milk was the highest among the four breeds. Therefore, use

of a mixed herd of different breeds for balanced volume, Hygiene in milking and milk handling is of obvi-

fat and protein concentrations, and SCC to meet regulatory ous importance to regulations for bacterial numbers and

requirements and for cheese and yogurt manufacturing is SCC that vary among countries and economic-cooperating

a consideration. regions. Delgado-Pertínez˜ et al. (2003) found that on

Spanish dairy goat farms a primary source of microbial

3.2. Litter size contamination was handling after harvest from the udder

through storage in the farm or cooperative tank, due to poor

Milk yield by goats, both dairy (Browning et al., 1995; hygiene or improper refrigeration. Both bacterial numbers

Carnicella et al., 2008; Delgado-Pertínez˜ et al., 2009a) and and SCC could be lessened by improved management con-

other breeds (Zahraddeen et al., 2009), can be affected by ditions, which included sanitation of the farm, animals, and

proliﬁcacy. Delgado-Pertínez˜ et al. (2009a) noted greater milking parlor, udder sealing, milking equipment mainte-

yield by Payoya autochthonous dairy goats of southern nance, and timely transportation after hand-milking to the

Spain in weeks 1–5 of lactation with two kids vs. one cooperative storage tank. There was a greater importance

regardless of natural suckling compared with machine- of good hygiene practices in wet vs. drier months and lower

milking. Conversely, during the post-weaning period of microbial numbers and SCC in milk harvested by hand than

weeks 6–30, milk yield was similar. Hence, it appears that machines, although this latter difference could have been

physiological differences such as in mammary gland devel- inﬂuenced by confounding factors such as breed.

opment during gestation (e.g., placental lactogen level;

Hayden et al., 1979) have greater impact on milk produc- 4.2. Intra-mammary infection

tion than differences in stimulation of lactation by suckling

(Browning et al., 1995). Similarly, based on tabular values, Somatic cells in goat milk are composed of different

Carnicella et al. (2008) noted similar daily milk yield by types of leukocytes (Dulin et al., 1982). In a study of 71

autochthonous Maltese goats of southern Italy with a litter goat herds, bulk tank samples had a distribution of 87% neu-

size of 1 or 2 in a post-weaning lactation period of 250–256 trophils, 9.9% macrophages, and 2.8% lymphocytes, with an

days. Likewise, Crepaldi et al. (1999) found less effect of average SCC of 1.3 × 10 /ml (Droke et al., 1993). In infected

litter size on milk yield in late lactation compared with udder halves, neutrophils and macrophages ranged from

earlier periods. Milk yield averaged 32 kg greater by Alpine 40 to 79 and 15 to 38%, respectively, and neutrophils and

goats with twins or triplets compared with singletons, even SCC increased with infection. High percentages of polymor-

though the kids were not allowed to suckle at birth. How- phonuclear neutrophils were found in goat milk with low

ever, this difference varied with parity, being greater for a SCC (<5 × 10 /ml), but they increased with stage of lacta-

parity of 1 vs. 3 (i.e., 563 vs. 15 kg). tion and age while levels of lymphocytes and macrophages

decreased.

3.3. Kid genotype In a Greek study throughout lactation, it was found

that streptococcal infections are rare in goats, in contrast

Kid or sire genotype can potentially inﬂuence milk pro- to dairy cows (Kalogridou-Vassiliadou, 1991). Mastitis-

duction via the suckling stimulus in a manner similar to related pathogens in normal goat milk samples were 59%

that of litter size. Likewise, the magnitude of such effects Staphylococcus spp., 30% Bacillus spp., 4% coliforms, 3%

would be inﬂuenced by litter size. An example is the 76- Micrococcus spp., 2% Streptococcus spp., 1% Corynebacterium

day study of Yiakoulaki et al. (2007) using Boer × Spanish spp., and 1% Pseudomonas spp. In a French study, 2% of

and Spanish does with twin-kid litters sired by Boer bucks udder halves were infected by S. aureus, 23% by coagu-

while grazing grass/forb pastures at different stocking rates lase negative staphylococci, and 75% were not infected

or with kids given access to additional pastures (i.e., creep (Lerondelle et al., 1992). Infection by S. aureus caused

grazing). Doe BW change was 25 and −59 g/day for Spanish high SCC of 7.9 × 10 /ml, while coagulase negative staphy-

× × 6 and Boer Spanish does, respectively, with similar ADG for lococci had 1.0 10 /ml and non-infected udder halves

the 50 and 75% Boer kids. It was postulated that a greater 5.2 × 10 /ml. Contreras et al. (1996) found that in a study

nutritional plane would have been necessary for Spanish of the physiological threshold of SCC in Spanish Murciano-

does to consume adequate nutrients to prevent or lessen Granadina goats, 18% of udder halves were infected and

A.L. Goetsch et al. / Small Ruminant Research 101 (2011) 55–63 59

that prevalent pathogens were 70% coagulase negative consuming 40% forage diets was 0.63 kg (31%) greater than

staphylococci and 1% coagulase positive staphylococci. for an 80% forage diet, with the dietary difference achieved

Contreras et al. (1999) reported a different distribution by varying levels of alfalfa hay and concentrate (Tovar-Luna

in a herd of 138 goats in the USA. With an incidence et al., 2010a,b). Research such as of Min et al. (2005) depict

of 34% intra-mammary infections, most pathogens were how nutritional value of the diet, in this case as varied by

staphylococci (96%), and S. epidermidis was the predomi- different levels of concentrate supplementation of grazing

nant species (67%). The SCC was slightly higher in milk from Alpine goats and a mixed concentrate/alfalfa hay diet fed

udder halves with subclinical infection of S. epidermidis in conﬁnement, can affect productivity. That is, low quality

(1,840,000/ml) than in milk with other staphylococcal diets resulting in high tissue mobilization to support lac-

infections (1,552,000/ml). Results of culturing goat milk tation lessen the level at and time to peak yield as well as

samples for pathogen identiﬁcation were compared with persistency compared with diets higher in quality. In sup-

monthly SCC of 380 Alpine goats in a commercial herd port, Tufarelli et al. (2009) fed Jonica goats 65, 50, and 35%

in the USA (Wilson et al., 1995). More than 90% of the concentrate diets and noted peak milk yield of 2.48, 2.13,

difference in SCC was not related to intra-mammary infec- and 2.02 kg/day at 53, 46, and 45 DIM, respectively. Like-

tion. Positive culture results, increasing DIM, decreasing wise, yield averaged 2.24, 2.16, and 2.10 kg/day in the ﬁrst

milk yield, increasing parity, and winter months of late 60 days of lactation and 2.36, 2.28, and 2.23 kg/day in the

lactation explained 23% of total variation in SCC. Histolog- second 60 days for dietary concentrate levels of 65, 50, and

ical and pathological tests on fresh udder half tissues of 35%, respectively.

goats with low (950,000/ml), medium (1,500,000/ml), and The physical form of the diet can affect the production

high (3,300,000/ml) SCC revealed no changes in the mam- and composition of goat milk, although effects appear of

mary glands or other mastitic evidence (Zeng and Escobar, smaller magnitude than in dairy cattle. Lesser effects with

1995), indicating that healthy dairy goats with healthy goats could relate to shorter ruminal residence time of

udders may produce milk with >1.0 × 10 /ml, particularly digesta and a lower proportion of metabolizable energy

in late lactation. In a large scale monitoring study, White from volatile fatty acids (Sanz Sampelayo et al., 1998).

and Hinckley (1999) observed a 36% prevalence of intra- Sanz Sampelayo et al. (1998) noted improved efﬁcien-

mammary infection (both clinical and sub-clinical). They cies of energy and nitrogen utilization in dairy goats fed

further reported that elevated SCC alone was not a valid a diet with pelleted alfalfa vs. long alfalfa hay, but level

indication of mammary infection in dairy goats. of production varied with differences in metabolizable

energy intake. The only effect on milk composition was a

5. Nutrition and feeding practices greater level of casein due to pelleting, which was thought

a function of slightly greater digestible fat intake. It was

5.1. Concentrate level and types of feedstuffs suggested that the improved efﬁciency of nitrogen uti-

lization resulted from greater ruminal outﬂow of intact

Both the dietary concentrate level and nature of spe- protein with pelleted alfalfa and the difference in efﬁciency

ciﬁc concentrate and forage feedstuffs impact level of milk of energy use was because of greater energy mobilization

production and characteristics of milk and milk products, in response to pelleting. However, it is possible that a pre-

and it can be difﬁcult to partition their effects. An exam- sumed shorter time spent eating pelleted than long alfalfa

ple of this is the study of Álvarez et al. (2007) in which hay minimized heat production (Osuji, 1974; Goetsch et al.,

diets with 35 and 65% concentrate feedstuffs but simi- 2010).

lar in NDF concentration were fed to Majorero goats of Inﬂuences of different types of forages and concentrates

Spain in mid-lactation. Forage in the 65% concentrate diet on the FA proﬁle of goat milk and milk products depend

was wheat straw, and forage in the 35% concentrate diet on many factors. For example, Lucas et al. (2008) observed

included alfalfa pellets, saltbush, vinagrera, and barley hay. only minor differences in the proﬁle of FA in Rocamadour

Levels of fat in milk and cheese were greater for 35 vs. 65% cheese between diets based on fresh pasture forage or hay.

concentrate, although levels of medium-chain fatty acids This was attributed to a number of conditions, including a

(FA) were similar between diets in milk but in cheese were moderate to high dietary level of concentrate (36%), some

greater for 35% concentrate. Sensory properties were more degree of confounding of stage of lactation and forage type

favorable for cheese from milk produced by goats consum- and the level of fat provided by concentrate feedstuffs, and

ing the 35% concentrate diet, which presumably related to possibly small differences in the FA proﬁle between the two

differences in levels of medium-chain FA. general forage types. There was also an interaction in the

Effects of dietary concentrate level obviously depend cheese FA proﬁle between dietary concentrate level and

on forage quality. For example, Ngwa et al. (2009) noted forage type, with effect noted for diets based on pasture

similar milk yield by Alpine does consuming 40 and 60% forage but not hay. Expected relationships between the

forage diets in early, mid-, and late lactation periods prob- level of fat provided by concentrate and the FA proﬁle in

ably because dietary levels of dehydrated alfalfa pellets, cheese were observed, with increased levels of long-chain

a relatively high quality forage, and concentrate feed- FA and decreases in medium-chain FA presumably because

stuffs were varied. This facilitated greater intake of the of changes in absorption and de novo synthesis (Chilliard

60% forage diet throughout the experiment. Nonetheless, and Ferlay, 2004). Likewise, increases in speciﬁc long-chain

milk fat concentration was greater for the 60% forage diet, FA in milk and milk products with elevated levels of dietary

with a tendency (P < 0.08) for a corresponding difference FA vary with the FA proﬁle of the particular sources of fat

in milk fat yield. Conversely, milk yield by Alpine goats (Chilliard and Ferlay, 2004; Lucas et al., 2008).

60 A.L. Goetsch et al. / Small Ruminant Research 101 (2011) 55–63

Interactions between productive potential and dietary resulted in greater concentrations and yields of fat (0.37

concentrate or energy level are common. For example, percentage units and 12.2 g/day, respectively) and protein

Pagano et al. (2010) noted that greater milk yield and (0.51 percentage units and 15.5 g/day, respectively) with-

levels of protein and casein for Girgentana goats that out impacting dry matter intake or milk yield uncorrected

␣

were homozygous for strong S1-casein alleles compared for level of fat.

with goats homozygous for weak alleles and heterozygous Stage of lactation as impacting potential milk energy

occurred only with diets containing concentrate and not and protein yields can affect responses to added RUP. For

with a diet consisting solely of pelleted alfalfa hay. Selec- example, Goetsch et al. (2000) noted increased milk yield

tion of speciﬁc dietary ingredients was not allowed in this by Alpine goats consuming diets relatively high in RUP

study. Conversely, Avondo et al. (2009) allowed this same in the ﬁrst 5 week of a 16-weeks early lactation experi-

breed of goats homozygous for strong or weak alleles to ment but not later. Effects of RUP level in this particular

select among pelleted alfalfa hay, whole barley, whole corn, study were similar between primiparous and multiparous

whole faba bean, and pelleted sunﬂower meal for 3 weeks goats, although it is likely that the probability of increas-

after being fed a mixed diet. Milk yield was similar between ing production by adding RUP to meet the metabolizable

genotypes when the mixed diet was fed but was greater protein need increases with increasing milk yield poten-

from the strong vs. weak allele group when feedstuffs were tial up to the third or fourth lactation. Similarly, genetic

offered separately. The strong allele group consumed less merit can inﬂuence productive responses to dietary CP

faba bean, and in weeks 2 and 3 increased corn intake, also level. De la Torre et al. (2008) observed more efﬁcient

resulting in increased efﬁciency of milk production with utilization of nitrogen and energy by Malaguena˜ goats of

less nitrogen loss. Spain with high vs. low genetic capability for ␣S1-casein

Avondo et al. (2008) found considerable effects of production when consuming a diet with 13.6% CP but not

different periods of time grazing on milk composition. 17.7%. Factors responsible for these interactions were not

Girgentana goats of Italy were allowed to graze ryegrass clearly identiﬁed. However, an interaction in milk energy

0.75

pasture from 09:00 to 13:00 or 12:00 to 16:00 h. Forage yield (208, 293, 260, and 264 kJ/kg BW ) and a tendency

selected in the afternoon was higher in water soluble car- for an interaction in energy intake (1.43, 1.66, 1.55, and

0.75

bohydrate and lower in crude protein and linolenic acid. 1.64 MJ/kg BW for low CP-low capability, low CP-high

Forage intake and milk protein yield were greater for the capability, high CP-low capability, and high CP-high capa-

later grazing period, although total milk yield was simi- bility, respectively) imply excessive levels of total and

lar. Milk from goats grazing later in the day had a higher ruminally degraded CP in the 17.7% CP diet and perhaps

level of linolenic acid and a lower concentration of conju- an involvement of differences in dietary levels of speciﬁc

gated linoleic acid. It appeared that later grazing increased feedstuffs rather than only in CP concentration coupled

efﬁciency of nitrogen utilization and lessened ruminal bio- with interrelated genetic differences in potential for milk

hydrogenation of FA compared with the earlier grazing production and feed intake.

treatment.

5.3. Fat and fatty acids

5.2. Dietary protein level and type

Sanz Sampelayo et al. (2007) recently reviewed effects

Effects of dietary crude protein (CP) level on milk of dietary characteristics on fat in goat milk, with a num-

production and composition depend on the nature of ber of summarizations based on earlier reviews such

nitrogenous compounds as inﬂuencing metabolizable pro- as of Morand-Fehr et al. (2000). Physico-chemical char-

tein intake. Nonetheless, with dietary CP levels above acteristics of diets (e.g., particle size and non-extreme

capacity for use in milk synthesis, efﬁciency of CP use concentrate:forage levels) have only indirect effects on

will be relatively low regardless of CP source (De la Torre milk fat concentration via energy intake as inﬂuencing

et al., 2008). It has been suggested that dairy goats are less milk yield and dilution. With animals of moderate to low

responsive to dietary supplementation with rumen unde- milk production potential, such effects can be of relatively

graded protein (RUP) than dairy cattle (Huston and Hart, small magnitude, and in some cases if maximum milk yield

2002). Little or no effects (Lu et al., 1990; Sahlu et al., 1993) potential has been reached, milk fat concentration can be

or improvements (Sanz Sampelayo et al., 1999; Chowdhury increased. Forage source can affect milk fat independent

et al., 2002) in milk production or composition by goats of energy intake, an example being potential increases in

with increased dietary level of RUP have been noted in milk fat from precursors such as butyrate and long chain FA

speciﬁc experiments. Variable responses of dairy goats provided by corn silage. Very low dietary fat levels cause

to dietary RUP additions could relate at least in part to low milk fat concentration. Increased milk fat yield result-

inadequate consideration of metabolizable protein needs ing from dietary fat supplementation typically does not

or inaccurate descriptions of requirements or quantities decrease milk fat concentration; increases in milk fat con-

provided by the variety of feedstuffs consumed by goats. centration with dietary fat supplementation are usually

Advantages of use of requirements of metabolizable pro- greater in mid- and late lactation than earlier.

tein rather than CP are evidenced by results of Laudadio Queiroga et al. (2009) postulated that with a commonly

and Tufarelli (2010). Diets approximately 17.5% CP were assumed more rapid ruminal digesta passage rate by goats

fed to Jonica goats of southern Italy, with differences in than dairy cattle (Hart, 2000), negative effects of dietary fat

ruminal CP degradability achieved by use of soybean meal supplementation on ruminal ﬁber digestion and microbial

and urea vs. corn gluten meal. The corn gluten meal diet protein synthesis in goats are less (Chilliard et al., 2003).

A.L. Goetsch et al. / Small Ruminant Research 101 (2011) 55–63 61

If so, then on this basis alone it could also be postulated In early lactation of dairy breeds of goats, even with high

that higher dietary levels and greater levels of saturation diet quality metabolizable energy intake can be inadequate

would be required to elicit inﬂuences of similar magnitude to support milk yield, resulting in use of mobilized tissue

as in dairy cattle. Likewise, inﬂuences of fat supplementa- energy, which is also related to limited anabolic capacity of

tion on characteristics and quality of goat milk might occur adipose tissue before peak lactation (Chilliard et al., 1987,

at lower dietary levels and degrees of unsaturation of FA 1991). When tissue is mobilized to support milk produc-

than for dairy cattle. However, direct species comparisons tion, levels of C18:0 and C18:1 cis in milk increase and

in the same experiment are not available to thoroughly levels of medium-chain FA decline (Eknæs and Skeie, 2006).

evaluate these speculations. The level of depletion of adipose tissue in the body is also

Queiroga et al. (2009) added 3 or 5% cottonseed or sun- related to off-ﬂavors in milk. Eknæs et al. (2006) indicated

ﬂower oil to the diet of Moxotó goats of Brazil. Cottonseed that with mobilization of more than 30–40% of adipose tis-

oil at 5% decreased milk yield relative to no added fat, sue, lipoprotein lipase and lipolytic activity in milk reach

although milk fat concentration was increased by the 5% levels sufﬁcient to elicit excessive formation of free FA and

level and yield was elevated by both levels. Sunﬂower oil occurrence of rancid and tart ﬂavors.

did not affect fat concentration but at 5% increased fat

yield. The only difference in milk acceptance scores was a

6. Summary and conclusions

decrease for odor with 5% cottonseed oil. Likewise, the sole

difference in sensory scores was an increase in goatish odor

Effects of production systems based on grazing and

for cottonseed oil at 5%, although there was a lower ran-

browsing vs. use of harvested feedstuffs in conﬁnement

cid ﬂavor for the control treatment compared with those

largely depend on speciﬁc feedstuffs and plants available

with added fat. This latter difference was suggested to have

and being consumed. Low forage nutrient ingestion should

resulted from greater lipolysis with elevated milk concen-

have relatively greater impact on tissue mobilization than

tration due to fat supplementation.

milk production in early than later periods of lactation,

Eknæs et al. (2009) supplemented Norwegian Dairy

with a transition to proportionally greater change in milk

Goats with sunﬂower oil at 4% or saturated long chain FA

production in late lactation. When tissue is mobilized to

at 6% of concentrate being given at 0.7 or 0.9 kg/day during

support milk production in early lactation, levels of C18:0

a 25-week experiment. Milk concentrations of fat, protein,

and C18:1 cis in milk increase and levels of medium-chain

and lactose were not affected by supplementation treat-

FA decline. Extended lactations offer opportunities to min-

ments. However, the saturated long chain FA treatment

imize or avoid seasonal ﬂuctuations in milk production

resulted in the lowest frequency of rancid taste, presum-

and lessen production costs. There appears relatively lit-

ably because of lower levels of C6:0-C10:0 and higher levels

tle potential for beneﬁt in milk yield from natural suckling

of C16:0 and C18:0. Factors responsible for the effect of

compared with machine milking. The magnitude of effects

supplementation with saturated long chain FA could not

of milking frequency on milk yield is less for goats of low

be conclusively discerned. But, it was postulated that at

vs. high production potential and low vs. high diet quality.

least part of the effect related to a positive inﬂuence of the

Both the dietary concentrate level and nature of speciﬁc

elevated level of C16:0 on stability of the milk fat globule

concentrate and forage feedstuffs impact level of milk pro-

membrane that lessened lipolysis and off-ﬂavor.

duction and characteristics of milk and milk products, and

Sanz Sampelayo et al. (2004) investigated carryover

it can be difﬁcult partition effects. Effects of elevated lev-

effects of fat supplementation in late lactation. Granad-

els of dietary FA on speciﬁc long-chain FA in milk and milk

ina goats in a semi-extensive production system were

products vary with the FA proﬁle of the particular sources

supplemented with 1 kg of concentrate containing 9%

of fat.

rumen-protected polyunsaturated FA for 3 weeks. There-

after, for 3 weeks a supplement without added FA was

Conﬂicts of interest

given. Milk, fat, and protein yields were increased by FA

during and for 1.5 weeks after supplementation with FA,

The authors A.L. Goetsch, S. Zeng, and T.A. Gipson do not

with a greater polyunsaturated FA level in milk fat observed

have a ﬁnancial or personal relationship with other peo-

during but not after FA feeding. It was postulated that

ple or organizations that could inappropriately inﬂuence

utilization of metabolizable energy may have been more

or bias the paper entitled “Factors inﬂuencing goat milk

efﬁcient both when FA were supplemented and for the next

production and quality.”

1.5 weeks, although supportive measures were not made. It

is conceivable that with similar or lower feed intake when

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