Characterization of the acute lactational response to trans-10, cis-12 conjugated linoleic acid

Trans-10, cis-12 conjugated linoleic acid (CLA) is a potent inhibitor of milk fat synthesis in the dairy cow. The decrease in milk fat yield during abomasal infusion of CLA reaches a nadir after 3 to 5 d. The acute responses to CLA were evaluated using 4 cows in a crossover design. Cows were milked with the aid of oxytocin every 4 h from −28 to 80 h and every 6 h from 86 to 116 h relative to the initiation of abomasal CLA infusion. An initial priming dose of 7.5 g of CLA was given at time zero followed by infusion of 2.5 g every 4 h for 72 h. Plasma CLA reached a near-steady-state concentration by 4 h, and initial plasma enrichments were greatest in the triglyceride and nonesterified fatty acid fractions. Milk CLA concentration peaked at 6 h and reached steady state by 22 h. At termination of the infusion, decreases in milk CLA concentration and yield and plasma CLA concentration were best fit by a reciprocal-linear function. Milk fat percentage decreased progressively after 2 h and was significant by 14 h. Milk fatty acid profile was initially unchanged, but between 18 and 36 h after initiation of the CLA dose the proportions of fatty acids progressively shifted, resulting in an increase in fatty acids >C16 and a decrease in fatty acids