Ruminant Nutrition II

The aim of this experiment was to determine the effects of conjugated linoleic acid (CLA) on milk production and composition, and milk fatty acid profile of dairy Holstein cows. Three lactating Holstein cows (203 ± 9 DIM; mean ± SD) fitted with rumen fistula were used in a 3 × 3 Latin square experiment with 21-d periods, including a 14-d adaptation period followed by a 7-d sampling period. Treatments were: 1) control (115 g/d calcium salts of palm fatty acids), 2) rumen protected CLA (120 g/d of lipid-encapsulated CLA), and 3) unprotected CLA (40 g/d unprotected CLA that replacing and balancing by Ca salts of palm fatty acids). Each dose provided 96 g/d fatty acids. Both of CLA supplements provided 12 g/d of trans-10, cis-12 CLA. Supplements were administered intraruminally once per day immediately before morning feeding. Individual milk yield and dry matter intake were recorded daily and milk composition was determined every day. Data were analyzed by MIXED procedure of SAS. Dry matter intake and milk yield were not affected by CLA supplements. The CLA supplements reduced milk fat content compared with control (P < 0.01), which were 2.58, 3.51, and 3.77 for rumen protected CLA, rumen unprotected CLA and control, respectively. In contrast, there were no significant differences in content of Milk protein and lactose between treatments. The milk fatty acid profile was significantly affected by rumen protected CLA. The proportion of shortand medium-chain fatty acids decreased in rumen protected CLA compared with control whereas the proportion of long-chain fatty acids increased in rumen protected CLA. The milk fat content of trans-10, cis-12 CLA was increased by CLA supplements compared with control (P < 0.01) especially by rumen protected CLA. The Δ9-desaturase index was not affected by CLA supplements. The results of this experiment indicated that rumen protected CLA could decrease milk fat content and yield, and alter milk fatty acid profile, but has no effect on dry matter intake and milk yield during late lactation in Holstein dairy cows.