Factors Affecting Goat Milk Production and Quality
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Small Ruminant Research 101 (2011) 55–63 Contents lists available at SciVerse ScienceDirect Small Ruminant Research jou rnal homepage: www.elsevier.com/locate/smallrumres 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. © 2011 Elsevier B.V. All rights reserved. 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 0921-4488/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2011.09.025 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 5 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.