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Although the effect of lactation stage is similar, the responses of milk yield and composition (fat and protein contents) to different types of lipid supplements differ greatly between goats and cows. Milk fat content increases with almost all studied fat supplements in goats but not in cows. However, the response of milk fatty acid (FA) composition is similar, at least for major FA, including conjugated linoleic acid (CLA) in goats and cows supplemented with either protected or unprotected lipid supplements. Goat milk CLA content increases sharply after either vegetable oil supplementation or fresh grass feeding, but does not change markedly when goats receive whole untreated oilseeds. Important interactions are observed between the nature of forages and of oil supplements on trans-10 and trans-11 C18:1 and CLA. Peculiarities of goat milk FA composition and lipolytic system play an important role in the development of either goat flavor (release of branched, medium-chain FA) or rancidity (excessive release of butyric acid). The lipoprotein lipase (LPL) activity, although lower in goat than in cow milk, is more bound to the fat globules and better correlated to spontaneous lipolysis in goat milk. The regulation of spontaneous lipolysis differs widely between goats and cows. Goat milk lipolysis and LPL activity vary considerably and in parallel across goat breeds or genotypes, and are low during early and late lactation, as well as when animals are underfed or receive a diet supplemented with protected or unprotected vegetable oils. This could contribute to decreases in the specific flavor of goat dairy products with diets rich in fat.
Chilliard et al. (Thu,) studied this question.