How Milk Secretion Differs in Goats and Cattle

The most obvious difference in anatomy is that there are only two teats on the goat udder vs. four on cow udders. Less obvious is the relatively larger inside volume of the teat and gland cysterns. That is why good goat udders look much more collapsed and emptier after milking than cow udders. The smaller, tighter diameter of the teat sphincter and meatus of goat udders makes milking and milking-out somewhat different. Also, the milk let-down effect in goats takes only a few seconds compared to one minute in cows.

Goat manure should always be pellets and drier than cow manure, which is much higher in water content or normally sloppy and easily soiling the flanks and udders of cows, while goats stay normally dry and have clean flanks and udders. This difference makes milking preparation procedures for goats easier to be sanitary. It is not risky to only dry clean goat teats and udders for the milking of low-bacteria-count goat milk. Also, prevalent bacteria and pathogens in goat udders are often of different species than in cow udders.

Seasonal reproduction, usual in the United States, is another important difference in milking goats. Cows are bred in every month of the year; therefore, their milk is always a composite of early, middle, and late-stage lactation. Goats, unless specially treated, breed only in early fall and are fresh only in early spring. Thus, at various times of the year, dairy goats are all in the early, or middle, or late stage of lactation, accentuating normal seasonal milk composition changes, that are related to stages of lactation, to estrus and low amounts of milk. For example, fat, protein, and somatic cells in milk normally are high in early and late lactation in cows and in goats, while lactose is usually the opposite.

All these differences might create doubts about the validity of using the same standards for evaluating milk of the two species. Not surprisingly, the compositional differences are also part of physiological differences in the secretion process of milk from inside the udder from the alveolar cells. Cow milk secretion has been termed “merocrine,” which is defined as “the act of secretion leaves the cell intact.” Goat milk secretion, on the other hand, has been termed by researchers “apocrine,” which is defined as “the secretion-filled free end of a gland cell is pinched off, leaving the nucleus and most of the cytoplasm to recover and repeat the process.”

Provided by the University of Delaware Cooperative Extension

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