Evaluating effects of fish meal on milk fat yield of dairy cows.

Experiment 1 measured the effect of different amounts of dietary fish meal on milk yield and composition. Milk fat percentage and yield were decreased by increased fish meal intake, but this change was not associated with changes in ruminal fermentation patterns. Plasma long-chain n-3 polyunsaturated fatty acids were increased as intake of fish meal increased. Ruminal disappearance of DM, CP, and lipid in fish meal was measured in situ. Seventy percent of lipid disappeared by 8 h. Intraruminal administration of fish oil did not alter ruminal fermentation and only slightly changed fatty acid profiles in duodenal digesta, plasma, or milk. Duodenal infusion increased plasma n-3 fatty acids but did not affect composition of fatty acids in milk. Experiment 2 compared effects of dietary fish meal and fish oil on milk production and composition. Fish meal increased n-3 fatty acids in plasma compared with those of the fish oil treatment. No changes were found in milk yield or composition because of experimental treatments. Cows fed fish meal or fish oil differed significantly in plasma fatty acid profiles but did not differ in ruminal VFA concentrations or milk fat yield.