Dose response of milk fat to intravenous administration of the trans-10, cis-12 isomer of conjugated linoleic acid.

Intravenous infusion of conjugated linoleic acid (CLA) was evaluated as a simpler method than abomasal infusion and the feeding of calcium salts to examine milk fat depression. The objectives were to determine the dose-dependent response of milk fat and plasma metabolites to intravenous administration of the trans-10, cis-12 isomer of CLA, an isomer identified to possess an inhibitory effect on milk fat synthesis. Four multiparous Holstein cows averaging 123 +/- 30 d in milk were randomly assigned to treatments in a 4 x 4 Latin square design. Catheters were inserted into the jugular vein for infusions and blood sampling. Treatments consisted of intravenous infusions of 0, 2, 4, and 6 g/d CLA (> 95% trans-10, cis-12 CLA). Infusates contained 72 g/d of a parenteral solution, saline, and CLA to 90 ml. Periods were of 5 d duration with a 7 d wash out. Milk was sampled at each milking and analyzed for fat, protein, and fatty acids. Blood samples were obtained on the last day of each period. Dry matter intake (22.4 +/- 2.4 kg/d), milk yield (28.5 +/- 3.3 kg/d), and protein percent (3.26 +/- 0.08%) of cows were not affected by treatment. However, milk fat percentage was reduced linearly with increasing doses of CLA. Milk fat percentage was 4.17, 3.53, 3.29, and 2.92% on d 5 for treatments 0, 2, 4, and 6 g/d CLA, respectively. Concentrations (4.2 mg/g of fat) of cis-9, trans-11 CLA in milk fat were not affected by treatment. However, an increase in the trans-10, cis-12 CLA content of milk fat was observed. Milk fat contained 0.00, 0.02, 0.06, and 0.10 mg of trans-10, cis-12 CLA per g of fat (SEM = 0.065) for treatments 0, 2, 4, and 6 g/d CLA, respectively. Plasma NEFA concentration increased linearly with the dose of the trans-10, cis-12 CLA. Intravenous infusion of the trans-10, cis-12 isomer of CLA depressed milk fat in a linear manner over the range of infusion studied and, therefore, is an alternative to abomasal infusion.