Whole-body propionate and glucose metabolism of multiparous dairy cows receiving folic acid and vitamin B 12 supplements.

This study was undertaken to evaluate the effect of supplementation of folic acid and vitamin B12 on glucose and propionate metabolism. Twenty-four multiparous cows were assigned according to a complete block design in a 2 × 2 factorial arrangement to one of the following treatments: (1) saline 0.9% NaCl, (2) 320 mg of folic acid, (3) 10 mg of vitamin B12 , or (4) 320 mg of folic acid and 10 mg of vitamin B12 . Intramuscular injections were given weekly from 3 wk before the expected calving date until 9 wk postpartum. At 63 d in milk, d-[6,6-2 H2 ]-glucose (16.5 mmol/h; jugular vein) and [1-13 C]-sodium propionate (13.9 mmol/h; ruminal vein) were simultaneously infused for 4 h; blood samples were collected from 2 to 4 h of the infusion period. Liver biopsies were carried out the following day. Supplements of folic acid and vitamin B12 respectively increased folate and vitamin B12 concentrations, both in milk and liver. Although dry matter intake was unaffected by treatments, milk and milk lactose yields tended to be lower by 5.0 and by 0.25 kg/d, respectively, for cows receiving the folic acid supplement. Plasma β-hydroxybutyrate concentration with the folic acid supplement followed the same tendency. Hepatic gene expression of methylmalonyl-CoA mutase and S-adenosylhomocysteine hydrolase was higher for cows receiving the combined folic acid and vitamin B12 supplement compared with cows receiving only the supplement of folic acid, whereas no treatment effect was noted for cows not receiving the folic acid supplement. Whole-body glucose rate of appearance and the proportion of whole-body glucose rate of appearance secreted in milk lactose decreased by 229 g/d and 5%, respectively, for animals receiving the folic acid supplement, concomitant with the lower milk lactose synthesis in these cows, indicating that supplementary folic acid may alter energy partitioning in cows. The absence of treatment effect on plasma concentrations of methylmalonic acid as well as on the proportion of glucose synthesized from propionate, averaging 60%, supports the fact that vitamin B12 supply was sufficient in control cows in the current study. Our results suggest that the folic acid supplement reduced glucose-derived lactose synthesis by redirecting glucose for other metabolic activity in the mammary gland or in other tissues.