Postruminal flow, digestibility, and utilization of fatty acylamides or conjugated linoleic acid for milk fat synthesis by lactating Holstein cows
Four Holstein cows with ruminal and duodenal cannulas were used to evaluate the effects of dietary fatty acylamides (canolamide) or abomasally infused conjugated linoleic acid on milk production and composition. In the first experiment, cows were fed diets with no supplemental fat(control), or the control diet supplemented at 3.3% of DM with canola oil, canolamide, or a mixture of equal amounts of canola oil and canolamide in a 4 x 4 Latin square. DMI and milk yield were decreased when cows were fed canolamide. Intake and duodenal flow of diet components and fatty acids were decreased by canolamide, but their apparent digestibilities were not affected by treatment. Fat supplementation decreased concentrations of fatty acids with 8 to 16 carbons and increased oleic acid in milk. In the second experiment, cows were infused abomasally with 100 g Linoleic acid (LA) or a mixture of 100 g LA plus 100 g conjugated linoleic acid (LA-CLA) for 24 h in a single crossover design. Infused CLA was a mixture of 70% cis-9, trans-11-18:2 and 30% trans-10, cis-12-18:2. Milk yield and DMI were not affected by treatment. Milk fat percentage and yield were decreased by LA-CLA. Concentration and yield of oleic and arachidonic acid and fatty acids with 6 to 16 carbons in milk were reduced by LA-CLA. Stearic acid and CLA concentrations in milk, however, were higher in response to LA-CLA. Infusion of LA-CLA led to increased (from 23 to 45%) concentration of unsaturated fatty acids with a concomitant decrease (from 70 to 42%) in saturated fatty acid concentration in milk fat. Feeding canolamide at 3.3% significantly decreased DMI and milk yield compared with canola oil or the mixture of canola oil and canolamide. However, results indicated that oleic acid and CLA concetration in milk fat can be increased proportionally to their flow into the small intestine. Utilization of these fatty acids for milk fat synthesis may cause a reduction in the amount of medium and short chain fatty acids synthesized de novo within the mammary gland. Furthermore, CLA appears to be a potent inhibitor of milk fat synthesis and desaturation of stearic and linoleic acid.