Ruminal Synthesis, Biohydrogenation, and Digestibility of Fatty Acids by Dairy Cows.

Ruminal synthesis and biohydrogenation of fatty acids in dairy cows were determined by sampling duodenal digesta through Tcanndas. Fatty acid digestibility in the t d tract also was measured. Five diets (concentrate:alfalfa hay:aUaIfa haylage:com silage, 2:1:1:1, DM) in a 5 x 5 Latin square contained either no added fat; 3 or 6% added calcium soap; or 3 or 6% animal-vegetable blend fat. Seventy percent of dietary fatty acids were recovered at the duodenum, and 106 g/d were synthesized in the rumen regardless of diets. Fatty acids synthesized in greatest amounts were odd or branched chains, whereas more than 90% of the fatty acids shorter than 14 carbons disappeared. Fatty acids in calcium soap were biohydrogenated 57% and in animal-vegetable blend 87%.  Fatty acids in calcium soap were more digestible (80.0 vs. 75.7%) than those in the blended fat due to greater unsaturation in the small intestine. Ruminal microorganisms selectively synthesized fatty acids.  Authors Abstract.