X. Qiu, M. L. Eastridge1, and J. L. Firkins
The Ohio State University Department of Animal Sciences
Abstract
Two experiments were conducted to verify our postulation that the production of conjugated linoleic acid (CLA) in dairy cows could be affected by solid passage rate, source and level of dietary fat, and ruminal pH. In Experiment 1, effects of high solid dilution rate (HSDR) (8 versus 4% per hour), high linoleic acid (HLA) (3 versus 1%), and low pH (LPH) (5.8 versus 6.5) were studied using a dual-flow continuous culture system with a 4 x 4 Latin square design. Each period consisted of 10 days with the last 3 days used for sample collection. The CLA flows were 9.42, 10.92, 14.52, and 12.48 mg/day for control, HSDR, HLA, and LPH, respectively. By increasing solid passage rate, dietary linoleic acid, and reducing pH, CLA flow from the rumen could be effectively elevated. In Experiment 2, effects of low DM intake (LDMI), feeding buffer (BUFF), and feeding soybean oil (SBO) were studied using four ruminally and duodenally cannulated cows with a 4 x 4 Latin square design. All diets contained 2% fish oil except SBO contained 2% soybean oil instead. The duodenal flows of CLA were 1060, 1482, 829, and 304 mg/day for control, LDMI, BUFF, and SBO, respectively. The CLA concentrations in milk were 24.5, 17.9, 18.5, and 10.1 mg/g of FA, respectively.
Feeding the SBO treatment resulted in the lowest CLA concentration in milk. The CLA in milk may result more from endogenous synthesis in the mammary gland than from ruminal biohydrogenation.