Abstract #T410

# T410
Apparent synthesis of vitamin B6 and folates in the rumen of lactating dairy cows fed alfalfa or orchardgrass silages.
D. S. Castagnino*1,2, M. Seck1,2, K. L. Kammes3, J. A. Voelker Linton3, M. S. Allen3, R. Gervais2, P. Y. Chouinard2, C. L. Girard1, 1Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada, 2Département des Sciences Animales, Université Laval, Québec, QC, Canada, 3Department of Animal Science, Michigan State University, East Lansing, MI.

Effects of forage family (legume vs. grass) on apparent ruminal synthesis and post-ruminal supply of vitamin B6 and folates were evaluated in 2 experiments. Diets containing either alfalfa (AL) or orchardgrass (OG) silages as the sole forage were offered to ruminally and duodenally cannulated lactating Holstein cows in crossover design experiments. Experiment 1 (E1) compared diets containing AL and OG (~27% total NDF) offered to 8 cows in 2 15-d treatment periods. Experiment 2 (E2) compared diets containing AL and OG (~30% total NDF) offered to 13 cows in 2 18-d treatment periods. Intake, duodenal flow and apparent ruminal synthesis (ARS) for each vitamin were analyzed using SAS mixed procedure. The experiments were analyzed separately. Differences were declared significant at P < 0.05. Vitamin B6 intakes were greater for AL than OG in E1 (368 vs. 236 ± 18.2 mg/d; P < 0.01) and E2 (180 vs. 77 ± 5.1 mg/d; P < 0.01). In contrast, folates intakes were lower for AL than OG in E1 (7.6 vs. 9.2 ± 0.51 mg/d; P = 0.02) and E2 (8.7 vs. 10.2 ± 0.29 mg/d; P < 0.01). In E1, duodenal flows of vitamins were not affected by treatment (vitamin B6, 72 ± 6.2 mg/d, P = 0.63; folates, 33 ± 4.2 mg/d, P = 0.15). In E2, duodenal flows of vitamin B6 were greater for AL than OG (59 vs. 31 ± 5.2 mg/d; P < 0.01) but the duodenal flows of folates were not affected by treatment (39 ± 2.7 mg/d; P = 0.78). Alfalfa increased the apparent ruminal degradation of vitamin B6 compared with OG in E1 (−294 vs. −167 ± 14.5 mg/d; P < 0.01) and E2 (−121 vs. −46 ± 4.9 mg/d; P < 0.01). The ARS of folates were not affected by treatment in either experiment (E1: 25 ± 3.9 mg/d, P = 0.19; E2: 30 ± 2.5 mg/d, P = 0.81). Combining data from both experiments, vitamin B6 intake was correlated positively with its duodenal flow (r = 0.68, P < 0.01) but negatively with ARS synthesis of the vitamin (r = −0.98, P < 0.01). Folates intake was correlated positively with its duodenal flow (r = 0.68, P < 0.01) and its ARS (r = 0.59, P < 0.01). Forage family affected the ruminal balance of vitamin B6 but had little or no effect on the post-ruminal supply of vitamin B6 and folates.

Key Words: dairy cow, vitamin B6, folates