Three Holstein cows were fed a high-concentrate diet (65:35 concentrate to forage) supplemented with either 5% sunflower oil (SO), 5% linseed oil (LO), or 2.5% fish oil (FO) to examine effects on biohydrogenation and fatty acid profiles in rumen, blood plasma, and milk. Diets were fed in a 3 x 3 Latin square with 4-wk periods with grass hay as the forage. Milk yield, dry matter intake, and percentages of milk fat (2.64) and protein (3.22) did not differ. All diets resulted in incomplete hydrogenation of unsaturated fatty acids as indicated by the profiles of 18:1 isomers, conjugated 18:2 isomers, nonconjugated 18:2 isomers, and 18:0 in ruminal fluid. Percentages of 8:0-14:0 and 16:0 in milk fat were greater with FO. Percentage and yield of trans10,cis12-18:2 were small and greater in cows fed SO (0.14%, 0.57 g/d) than FO (0.03%, 0.15 g/d) or LO (0.04%, 0.12 g/d). Percentage and yield of trans10-18:1, however, increased with FO (6.16%) and SO (6.47%) compared with LO (1.65%). Dietary FO doubled percentage of cis11-18:1 in rumen, plasma, and milk fat. Despite a lack of difference in ruminal percentage of trans11-18:1 (10.5%), cows fed FO had greater plasma trans11-18:1 (116 vs. 61.5 microg/mL) but this response did not result in greater trans11-18:1 percentage in milk fat, which averaged 5.41% across diets. Percentage (2.2%) and yield (14.3 g/d) of cis9,trans11-18:2 in milk fat did not differ due to oils. Unique responses to feeding LO included greater than 2-fold increases in percentages of trans13+14-18:1, trans15-18:1, trans16-18:1, cis15-18:1, cis9,trans12-18:2 and trans11,cis15 -18:2 in umen, plasma, and milk, and cis9,trans13-18:2 in plasma and milk. Ruminal 18:0 percentage had the highest positive correlation with milk fat content (r = 0.82) across all diets. When compared with previous data with cows fed high-concentrate diets without oil supplementation, results suggest that greater production of trans10-18:1, cis11-18:1, and trans11,cis15-18:2 coupled with low production of 18:0 in the rumen may be associated with low milk fat content when feeding high-concentrate diets and fish oil. In contrast, SO or LO could lead to low milk fat content by increasing ruminal trans10-18:1 (SO) or trans11,cis15-18:2 and trans9,trans12-18:2 (LO) along with a reduction in mammary synthesis of 8:0-16:0. Simultaneous increases in ruminal trans11-18:1 with fish oil, at a fraction of sunflower oil supplementation, may represent an effective strategy to maintain cis9,trans11-18:2 synthesis in mammary while reducing milk fat output and sparing energy.

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 5.0g/100g dry matter sunflower oil (SO), 5.0g/100g linseed oil (LO), or 2.5g/100g fish oil (FO). A 3×3 Latin square with 4-week periods was used. Grass hay was the forage. Biohydrogenation of 18:2n−6 was greater with SO (92%) than LO (0.85), and was lowest with FO (0.75). Cows fed LO had greater 18:3n−3 hydrogenation (0.95) compared with FO or SO (84%). Biohydrogenation of 20:5n−3 (EPA) and 22:6n−3 (DHA) with FO averaged 0.92 and 0.89. Flow of total conjugated linoleic acids (CLA) was greater in cows fed SO (8.3g/d) compared with FO (4.0g/d). Feeding LO resulted in flow of 6.9g total CLA/d. Percentage of cis9,trans11-CLA in duodenal lipids was 0.22g/100g total fatty acids with SO but only 0.06 or 0.13g/100g with FO or LO. trans10,cis12-CLA percentage was greater with SO (0.19g/100g) than FO or LO (0.04g/100g). Flow of total non-conjugated 18:2 isomers averaged 99.4g/d with LO and 60.3g/d with FO or SO. Percentage of trans11,cis15-18:2, derived from 18:3n−3 hydrogenation, ranked by treatment was LO (4.70g/100g)>FO (2.70g/100g)>SO (0.86g/100g). Total trans-18:1 flow did not differ due to diets (254g/d). trans10-18:1 percentage was greater in cows fed FO or SO (12.2g/100g) than LO (3.1g/100g). trans11-18:1 percentage averaged 10.8g/100g across diets. Flow of 18:0 was 3.8-fold greater in cows fed SO or LO (373g/d) than FO (96g/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 18:2n−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.

Trans-18:1 and 18:2 isomer composition in ruminal fluid during the daily feeding cycle was examined in 3 cows fed a high concentrate diet (35:65) with 5% (DM basis) sunflower oil (SO), 5% linseed oil (LO), or 2.5% fish oil (FO) in a 3 x 3 Latin square with 3 4-wk periods. Grass hay and concentrate mixtures were fed at 0900, 1300, and 1700 h daily. Ruminal fluid was collected at 0900, 1100, 1300, 1500, 1700, 2000, and 0000 h. Feeding SO resulted in the greatest mean concentrations (% of total fatty acids) of trans10,cis12-18:2 and cis9,trans11-18:2. In particular, trans10,cis12-18:2 with SO was greater at 1500 (0.29%), 2000 (0.34%), and 0000 h (0.25%) relative to 0900 h (0.07%). Cis9,trans11-18:2 concentration increased from 0.47% at 0900 h to a peak of 2.06% at 1100 h; it remained greater than the percentage determined at 0900 h at 1300 (1.4%) through 0000 h (1.1%). Concentration of trans11,cis15-18:2 was greatest with LO, ranging from 3.3% (0900 h) to a peak of 11.4% at 2000 h. Mean trans10-18:1 concentration ranked by diet was SO > FO > LO. Peak trans10-18:1 with SO was observed at 1700 h (14.9%) compared with 0900 h (5.1%). Trans11-18:1 did not differ with diet or time. Stearic acid decreased over time with all diets reaching minimum concentrations at 1700 to 2000 h relative to 0900 h. Feeding FO, however, decreased mean 18:0 concentration 4-fold compared with LO or SO. The moderate effect on concentration of trans-18:1 coupled with accumulation of 18:2 intermediates and the decrease of 18:0 over time suggest that oils reduced the biohydrogenation of 18:2 isomers to trans-18:1.

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.

The effect of linseed oil (LSO) supplementation on total-tract and ruminal nutrient digestibility, N metabolism, and ruminal fluid characteristics was investigated in dairy cows fed diets containing different forage to concentrate ratios (F:C). The experimental design was a 4 x 4 Latin square with 2 x 2 factorial arrangement of treatments. Four lactating Holstein cows were fed a forage-rich diet without LSO (F; F:C = 65:35, dry matter basis), a forage-rich diet with LSO (FO; F:C = 65:32, 3% LSO), a concentrate-rich diet without LSO (C; F:C = 35:65), or a concentrate-rich diet with LSO (CO; F:C = 35:62, 3% LSO). Total-tract digestibility of DM and OM was greater with supplemental LSO. A tendency for greater total-tract digestibility of NDF and ADF also was observed in cows fed LSO. Ruminal digestibility of NDF or ADF decreased when CO was fed compared with C. In contrast, feeding FO increased NDF or ADF digestibility compared with F. Although ruminal starch digestion was nearly complete with all diets, digestibility was greater when cows were fed C or CO compared with F or FO. Bacterial N flow to the duodenum decreased when FO was fed compared with F. In contrast, feeding CO increased bacterial-N flow compared with C. Neither F:C nor LSO supplementation affected ruminal pH or total VFA concentration in ruminal fluid. However, molar proportion of propionate was greater with C or CO compared with F or FO and increased with LSO supplementation regardless of F:C. Molar proportion of n-butyrate decreased with LSO supplementation. Total protozoal numbers in ruminal fluid decreased markedly only when CO was fed. Overall, data show that feeding LSO had no negative effects on total-tract digestion in dairy cows but may decrease ruminal fiber digestibility when fed with high-concentrate diets. The widely spread idea that LSO decreases digestibility, arising from studies with sheep, did not seem to apply to lactating cows fed 3% LSO.