Biohydrogenation, duodenal flow, and intestinal digestibility of trans fatty acids and conjugated linoleic acids in response to dietary forage:concentrate ratio and linseed oil in dairy cows

Duodenal flows of hydrogenation intermediates in response to changes in dietary forage: concentrate ratio ( F: C) and linseed oil were evaluated using 4 lactating Holstein cows fed a low ( 65: 35 forage to concentrate) or high ( 35: 65) concentrate diet without (LC, HC) added oil or with linseed oil (LCO, HCO) at 3% of DM. A 4 x 4 Latin square design was implemented for 5 wk. Lower hydrogenation of 18: 2n-6 and 18: 3n-3 was observed with HC, but it increased with LCO or HCO. Duodenal flow of total conjugated linoleic acids (CLA) increased by 1.40 (LCO) to 3.01 (HCO) g/d with linseed oil. This response was associated with greater flows of cis9, trans11- (+ 0.21 to + 0.55 g/d), trans11, cis13- (+ 0.33 to + 0.36), trans11, trans13- (+ 1.01 to + 1.15 g/d), and trans, trans-CLA (+ 0.12 to + 0.72 g/d). Trans10, cis12-CLA flow averaged 0.08 g/d and was not affected by F: C or oil. trans11, cis15-18: 2 flow increased by 8.5 ( LCO) to 62 (HCO) g/d in response to linseed oil. Total trans-18: 1 flow was 37 g/d in cows fed LC and increased to 81 g/d with HC. Feeding oil increased total trans-18: 1 to the greatest extent with HCO. Flow of trans10-18: 1 was lower with LC than with HC (1.46 vs. 20 g/d). Linseed oil increased trans11- 18: 1 flow by 40 ( LCO) to 113 g/d ( HCO). Feeding LCO and HCO also increased flows of trans6+7+8-, trans13+14-, trans15-, and trans16-18: 1. Apparent intestinal digestibility of trans-18: 1 isomers was largely unaffected by concentrate level and ranged between 67 and 95%. Linseed oil increased digestibility of nearly all isomers by 3 to 16 percentage units. Digestibility of cis9, trans11- CLA was greater in cows fed HC (55%) compared with cows fed LC (32%) and was not affected by linseed oil. Data suggest that high concentrate diets enhanced ruminal outflow of trans10- 18:1. We provide initial in vivo evidence that supplemental 18: 3n-3 is hydrogenated to trans11, cis15-18: 2, trans11-18: 1, trans13+14-18: 1, trans15-18: 1, trans6+7+8- 18: 1, and trans16-18: 1 primarily.