Abstract
Ruminal hydrogenation and duodenal flow of fatty acids were evaluated in three lactating Holstein cows fed a diet with a high concentrate:forage ratio (65:35) plus 5.0 g/100 g dry matter sunflower oil (SO), 5.0 g/100 g linseed oil (LO), or 2.5 g/100 g fish oil (FO). A 3 × 3 Latin square with 4-week periods was used. Grass hay was the forage. Biohydrogenation of 18:2 n − 6 was greater with SO (92%) than LO (0.85), and was lowest with FO (0.75). Cows fed LO had greater 18:3 n − 3 hydrogenation (0.95) compared with FO or SO (84%). Biohydrogenation of 20:5 n − 3 (EPA) and 22:6 n − 3 (DHA) with FO averaged 0.92 and 0.89. Flow of total conjugated linoleic acids (CLA) was greater in cows fed SO (8.3 g/d) compared with FO (4.0 g/d). Feeding LO resulted in flow of 6.9 g total CLA/d. Percentage of cis9, trans11-CLA in duodenal lipids was 0.22 g/100 g total fatty acids with SO but only 0.06 or 0.13 g/100 g with FO or LO. trans10, cis12-CLA percentage was greater with SO (0.19 g/100 g) than FO or LO (0.04 g/100 g). Flow of total non-conjugated 18:2 isomers averaged 99.4 g/d with LO and 60.3 g/d with FO or SO. Percentage of trans11, cis15-18:2, derived from 18:3 n − 3 hydrogenation, ranked by treatment was LO (4.70 g/100 g) > FO (2.70 g/100 g) > SO (0.86 g/100 g). Total trans-18:1 flow did not differ due to diets (254 g/d). trans10-18:1 percentage was greater in cows fed FO or SO (12.2 g/100 g) than LO (3.1 g/100 g). trans11-18:1 percentage averaged 10.8 g/100 g across diets. Flow of 18:0 was 3.8-fold greater in cows fed SO or LO (373 g/d) than FO (96 g/d). Apparent intestinal digestibility (proportion of duodenal flow) of trans9- through trans12-18:1 was greater with FO (range 0.94–0.96) than SO (0.91–0.93), and intermediate with LO (0.92–0.95). Digestibility of cis9, trans11-CLA was greater in cows fed SO (0.85) compared with FO (0.63) or LO (0.79). trans10, cis12-CLA digestibility was greater with FO or SO (0.97) than LO (0.86). Dietary EPA and DHA from fish oil (at only 0.16 of total fatty acid intake) inhibited the reduction of trans-18:1 to 18:0 during hydrogenation of unsaturated fatty acids in the basal diet and led to marked accumulation of trans10-18:1. Intake of 18:2 n − 6 with FO was not associated with greater flow of trans10-18:1. The effect of FO on biohydrogenation may have been associated with a combination of factors such as greater numbers of ruminal protozoa and(or) increased isomerization of trans11-18:1 to trans10-18:1 in the rumen.
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