Effects of different fat mixtures on milk fatty acid composition and oxidative stability of milk fat

The experiment was carried out to determine effects of different fatty acids (FA) mixtures on milk FA composition and milk fat oxidation change. Thirty-six dairy cows were used in a completed design experiment for 8 weeks. Cows were fed one of three lipid supplements (1) short- and medium-chain fatty acids (SMCFA), (2) butterfat, and (3) long-chain fatty acids (LCFA). Data were analyzed using MIXED procedure of SAS. Daily dry matter intake (DMI), milk yield, and milk protein, total solids (TS), lactose, free fatty acids (FFA) content were unaffected among 3 treatments, whereas milk fat concentration was decreased (P<0.05) as carbon chain length increased in supplement lipid. Relative to SMCFA, 12:0, 14:0 and 16:0 concentrations in milk fat from cows on butterfat and LCFA treatment were decreased (P<0.05). Proportions of cis9-18:1, trans9-C18:1, and cis9, trans11-conjugated linoleic acid (CLA) were increased by 15.5, 74.3, and 20.3% (P<0.05) in milk fat from cows on LCFA compared with cows on SMCFA. Similar increases in trans9-18:1, trans11-18:1, cis9, trans11-CLA, 18:2n-6 and 18:3n-3 were 34.2, 31.5, 21.4, 11.0, and 15.4% (P<0.05) in butterfat treatments, respectively. Furthermore, activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were decreased (P<0.05) when increased long-chain FA in diets, while concentration of malondialdehyde (MDA) was increased (P<0.01) in bovine milk. Our results indicated that long-chain FA exhibit positive effects on milk FA composition, but may decrease oxidative stability of milk fat.