Effects of ruminal or postruminal fish oil supplementation on intake and digestion in dairy cows.

The effect of fish oil supplementation on intake, digestibility and the volatile fatty acid profile in dairy cows was investigated in two trials. In each of the two trials, six cows received a diet based on maize silage in a latin square design. In the first trial, the cows were fitted with ruminal and duodenal cannulae and their diet was either supplemented or not with 300 mL fish oil and infused either into the rumen or the duodenum. In the second trial, the cows were not cannulated and their diet was either supplemented or not with 200 or 400 mL fish oil given orally. In both trials, the fish oil reaching the rumen decreased (P < 0.01) feed intake, increased (P < 0.01) the organic matter and fibre digestibility, and the percentage of propionate in the volatile fatty acid profile. These increases were higher for the 400 mL supplement than for the 200 mL one. The long-chain fatty acid pattern in the duodenum showed a high degree of hydrogenation of 20- and 22-carbon fatty acids. All these results demonstrated the particular action of fish oil on ruminal digestion when compared to other lipid sources.