Effects of diet and physiological factors on milk fat synthesis, milk fat composition and lipolysis in the goat: A short review

The current short review summarizes recent data on the specificities of goats compared with cows, of milk fatty acid (FA) secretion and milk fat lipolysis responses to physiological and nutritional factors. The influence of lactation stage on milk fat yield and FA composition is similar between goats and cows. In contrast, changes in milk fat yield and composition to diet, lipid supplements in particular, differs between the two ruminant species. In almost all cases, dietary lipid supplements increase milk fat content in goats, but not in cows. The goat is much less sensitive to diet-induced alterations in ruminal biohydrogenation pathways causing trans-10 18:1 to replace trans-11 18:1 as the major intermediate relative to the cow. Mammary lipid secretion in the goat is also less sensitive to the anti-lipogenic effect of trans-10,cis-12 conjugated linoleic acid (CLA) compared with the cow. Consistent with these observations, mammary lipogenic gene expression is less affected by diets rich in starch and polyunsaturated FA (PUFA) in goats than cows. However, diets containing PUFA induce much greater changes in delta-9 desaturase gene expression in goats compared with cows, that may be related to differences in the availability of biohydrogenation intermediates at the mammary glands (e.g. trans-9,trans-11-CLA). The development of either goat flavour or rancidity is related to the inherent peculiarities of milk FA composition and lipolytic system in this species. In contrast with cows, milk LPL activity and lipolysis are low during early and late lactation in goats, and are decreased when animals are underfed or receive a diet supplemented with plant oils. In goats the alpha-s1-casein (CSN1S1) gene polymorphism is associated with a decrease in milk fat content and 8:0-12:0 concentrations in the low CSN1S1 genotype. Conversely, milk fat product/substrate concentration ratios for delta-9 desaturation and spontaneous lipolysis are increased in the low genotype.