Review article
Factors affecting goat milk production and quality

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Abstract

Differences between production systems based on grazing and browsing vs. use of harvested feedstuffs in confinement largely depend on specific feedstuffs and plants available and being consumed. Low forage nutrient ingestion should have relatively greater impact on tissue mobilization than milk production in early than later periods of lactation, with a transition to proportionally greater change in milk production in late lactation. However, low body condition at kidding would limit tissue energy mobilization and restrict impact 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 compared 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.

Introduction

There are many types of goats raised under quite varied production conditions throughout the world. Findings in one particular setting may not always apply to others. Goats of dairy breeds highly selected for milk production receive more research consideration regarding milk yield and quality. However, the physiological state of lactation is also integral to the rearing of all other genotypes and important to food and economic securities of millions of people. Therefore, this research summary is not restricted to dairy goat genotypes. Hence, in many locations in the manuscript some information about goat genotype and production conditions is included. The objective of this paper is to provide an overview of some of the recent research regarding factors that influence the production and quality of goat milk.

Section snippets

Production systems

Because diet affects the composition of goat milk and milk products, differences between production systems based on grazing and browsing vs. use of harvested feedstuffs in confinement largely depend on specific feedstuffs and plants available and being consumed. As an example, Galina et al. (2007) observed many differences in the composition of soft cheese made from milk of goats fed indoors compared with ones grazing rangeland with a diverse array of plant species, although the diet of

Genotype

Milk yield can be defined mathematically as the area under the lactation curve, with many factors affecting the shape and scale of the curve and, thus, overall yield (Gipson and Grossman, 1990). Genetic effects are manifested individually and collectively. Individual genetic effects can be seen in the expected progeny differences that are calculated annually by USDA-AIPL (Wiggans and Hubbard, 2001). Collectively, genetic differences are seen as breed differences, with the Swiss breeds (Alpine,

Hygiene

Hygiene in milking and milk handling is of obvious importance to regulations for bacterial numbers and SCC that vary among countries and economic-cooperating regions. Delgado-Pertínẽz et al. (2003) found that on Spanish dairy goat farms a primary source of microbial contamination was handling after harvest from the udder through storage in the farm or cooperative tank, due to poor hygiene or improper refrigeration. Both bacterial numbers and SCC could be lessened by improved management

Concentrate level and types of feedstuffs

Both the dietary concentrate level and nature of specific concentrate and forage feedstuffs impact level of milk production and characteristics of milk and milk products, and it can be difficult to partition their effects. An example of this is the study of Álvarez et al. (2007) in which diets with 35 and 65% concentrate feedstuffs but similar in NDF concentration were fed to Majorero goats of Spain in mid-lactation. Forage in the 65% concentrate diet was wheat straw, and forage in the 35%

Summary and conclusions

Effects of production systems based on grazing and browsing vs. use of harvested feedstuffs in confinement largely depend on specific feedstuffs and plants available and being consumed. Low forage nutrient ingestion should have relatively greater impact on tissue mobilization than milk production in early than later periods of lactation, with a transition to proportionally greater change in milk production in late lactation. When tissue is mobilized to support milk production in early

Conflicts of interest

The authors A.L. Goetsch, S. Zeng, and T.A. Gipson do not have a financial or personal relationship with other people or organizations that could inappropriately influence or bias the paper entitled “Factors influencing goat milk production and quality.”

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    This paper is part of the special issue entitled Products from Small Ruminants, Guest Edited by A. Govaris and G. Moatsou.

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