High-Concentrate Diets and Polyunsaturated Oils Alter Trans and Conjugated Isomers in Bovine Rumen, Blood, and Milk

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 3×3 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 trans 10, cis 12-18:2 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 trans 10-18:1, however, increased with FO (6.16%) and SO (6.47%) compared with LO (1.65%). Dietary FO doubled percentage of cis 11-18:1 in rumen, plasma, and milk fat. Despite a lack of difference in ruminal percentage of trans 11-18:1 (10.5%), cows fed FO had greater plasma trans 11-18:1 (116 vs. 61.5μg/mL) but this response did not result in greater trans 11-18:1 percentage in milk fat, which averaged 5.41% across diets. Percentage (2.2%) and yield (14.3 g/d) of cis 9, trans 11-18:2 in milk fat did not differ due to oils. Unique responses to feeding LO included greater than 2-fold increases in percentages of trans 13+14-18:1, trans 15-18:1, trans 16-18:1, cis 15-18:1, cis 9, trans 12-18:2 and trans 11, cis 15 -18:2 in umen, plasma, and milk, and cis 9, trans 13-18:2 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 trans 10-18:1, cis 11-18:1, and trans 11, cis 15-18:2 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 trans 10-18:1 (SO) or trans 11, cis 15-18:2 and trans 9, trans 12-18:2 (LO) along with a reduction in mammary synthesis of 8:0-16:0. Simultaneous increases in ruminal trans 11-18:1 with fish oil, at a fraction of sunflower oil supplementation, may represent an effective strategy to maintain cis 9, trans 11-18:2 synthesis in mammary while reducing milk fat output and sparing energy.