Conjugated linoleic acids alter milk fatty acid composition and inhibit milk fat secretion in dairy cows.

摘要

Conjugated linoleic acids (CLA) have positive health effects in experimental animal models. The objective of this study was to determine the effect of CLA supplementation on milk fatty acid composition of dairy cows. A commercial source of CLA was infused abomasally to bypass rumen fermentation. The supplement contained 61.2% CLA. The major CLA isomers were cis/tran 8, 10, cis/trans 9, 11, cis/trans 10, 12 and cis/trans 11, 13. A total of 4 Holstein-Friesian cows were used in a 4 x 4 Latin square design. Treatments comprised of a 5-day infusion of 0, 50, 100 and 150 g/day of CLA supplement. Infusion increased the CLA content of milk fat from 6.8 mg/g fat (zero dose) to 63.6 mg/g fat (highest dose). All of the major CLA isomers in the supplement were transferred to milk fat in a dose-dependent manner. CLA infusion had no effect on milk protein and had little effect on milk yield (p&0.001). However, CLA infusion reduced milk fat (p&0.001). On average, the content and yield of milk fat were reduced by 52 and 55%, respectively. The role of specific CLA isomers and mechanisms for the reduction in milk fat had not been established, although the pattern of milk fatty acids demonstrated effects that were most pronounced on de novo fatty acid synthesis and desaturation process. Dietary supplementation of CLA increased the CLA content of milk fat, altered milk fatty acid composition and markedly reduced the milk fat content and yield..