Effects of forage-to-concentrate ratio on B-vitamin concentrations in different ruminal fractions of dairy cows.

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Source: Dairy Farmers of Canada

Canadian Journal of Animal Science (2005), Vol. 85 (3), p. 389-399. Girard, C.L., Berthiaume, R., Chiquette, J., Matte, J.J., AAFC, Dairy and Swine Research and Development Centre (Lennoxville, QC), Martineau, R., Département des sciences animales, Université Laval (Québec, QC), Mustafa, A.F. and Santschi, D.E., Department of Animal Science, McGill University (Sainte-Anne-de-Bellevue, QC).

Two studies were undertaken to verify the effect of the forage-toconcentrate ratio of the diet on B-vitamin concentrations in ruminal contents. In the first study, concentrations of biotin, folates and vitamin B12 were determined in rumen fluid and plasma of cows fed either high- or low-forage diets. In the second study, the authors evaluated the effects of forage-to-concentrate ratio on concentrations of seven B-vitamins in the particle-free fluid and in both liquid- and solid- associated bacteria. It was found that B-vitamins were present mainly in the bacterial fractions of the ruminal content; only very small amounts were found in the fluid surrounding it. Changing the forage-to-concentrate ratio has more effects on vitamin concentrations in the bacteria associated with the solid fraction in the rumen than with the liquid one. Most important effects of a low-forage diet were an increase in riboflavin but a decrease in true vitamin B12 concentrations in solidassociated bacteria, as well as a decrease in biotin concentration in particle-free fluid. It appears that ruminal B-vitamin concentration is altered by changes in the foragetoconcentrate ratio, which suggests that the supply of vitamins to dairy cows could be influenced by diet composition.