Fatty Acid Metabolism in the Digestive Tract of Lactating Cows Fed Tallow in Increasing Amounts at Two Feed Levels

Abstract

Long-chain fatty acid metabolism in the digestive tract was studied in lactating cows fed at two levels of dry matter intake (L, 8.6 kg DM and H, 12.6 kg DM), with 0, 4 and 6% added tallow at low feed level (L0, L4 and L6), and 0, 2, 4 and 6% fat at high feed level (H0, H2, H4 and H6). Mean fatty acid balance from mouth to duodenum was about zero when corrected for endogenous fatty acids from bile. However, regression analysis showed a microbial synthesis of 68 g at zero fatty acid intake, and a trend which indicated declining de novo synthesis of fatty acids with increasing fat level in the diet. As a mean 68% of the unsaturated C18 fatty acids were hydrogenated in the rumen.

Fatty acid and crude fat true digestibilities decreased with increasing fat intakes owing to a decrease in stearic acid (C18:0) digestibility.

Key Words:

• Digestibility
• microbial fatty acid synthesis
• biohydrogenation