Effects of increasing amounts of extruded linseed in the diet on apparent ruminal synthesis of some B vitamins in dairy cows

Many studies have shown that metabolic efficiency of ruminants can be significantly decreased when B-vitamin supply is insufficient. Under the present state of knowledge, the amounts of B vitamins available for intestinal absorption cannot be predicted based on diet composition. Therefore, in an attempt to increase our understanding of the effects of dietary factors, on B-vitamin supply for dairy cows, the effects of increasing amounts of extruded linseed in diets based on hay (permanent grassland hay,H; Experiment 1) or corn silage (CS; Experiment 2) on apparent ruminal synthesis (ARS) of thiamin, riboflavin, niacin, vitamin B-6, folates and vitamin B(12)were evaluated. In each experiment, four lactating Holstein cows fitted with cannulas in the rumen and the proximal duodenum were used in a 4 x 4 Latin square design. In both experiments, the dietary treatments consisted of an increasing supply of extruded linseed representing 0%, 5%, 10% or 15% of diet DM. The forage : concentrate ratios were 50 : 50 and 60 : 40 for Experiments 1 and 2, respectively. Duodenal flow was determined using YbCl(3)as a marker. The ARS of each B vitamin was calculated as duodenal flow - daily intake. In both experiments, treatments did not affect thiamin, riboflavin, niacin and vitamin B(12)duodenal flow or ARS. Increasing the dietary concentration of extruded linseed decreased folate intake in Experiment 1 and vitamin B(6)intake in Experiment 2 but resulted in a greater duodenal flow of vitamin B(6)and folates regardless of the forage used in basal diet. Greater dietary linseed concentrations decreased vitamin B(6)apparent degradation in the rumen in CS-based diet only and increased folate ARS in both H- and CS-based diets. Increasing linseed concentration of isonitrogenous and isoenergetic diets increased vitamin B(6)and folate supply to dairy cows, both with H- and CS-based diets.