Effects of dietary supplements of folic acid and vitamin B12 on metabolism of dairy cows in early lactation

The present experiment was undertaken to determine the effects of dietary supplements of folic acid and vitamin B-12 given from 3 wk before to 8 wk after calving on lactational performance and metabolism of 24 multiparous Holstein cows assigned to 6 blocks of 4 cows each according to their previous milk production. Supplementary folic acid at 0 or 2.6 g/d and vitamin B-12 at 0 or 0.5 g/d were used in a 2 x 2 factorial arrangement. Supplementary folic acid increased milk production from 38.0 +/- 0.9 to 41.4 +/- 1.0 kg/d and milk crude protein yield from 1.17 +/- 0.02 to 1.25 +/- 0.03 kg/d. It also increased plasma Gly, Ser, Thr, and total sulfur AA, decreased Asp, and tended to increase plasma Met. Supplementary B-12 decreased milk urea N, plasma Ile, and Leu and tended to decrease Val but increased homocysteine, Cys, and total sulfur AA. Liver concentration of phospholipids was higher in cows fed supplementary B-12. Plasma and liver concentrations of folates and B-12 were increased by their respective supplements, but the increase in plasma folates and plasma and liver B-12 was smaller for cows fed the 2 vitamins together. In cows fed folic acid supplements, supplementary B-12 increased plasma glucose and alanine, tended to decrease plasma biotin, and decreased K-m of the methylmalonylcoenzyme A mutase in hepatic tissues following addition of deoxyadenosylcobalamin, whereas it had no effect when cows were not fed folic acid supplements. There was no treatment effect on plasma nonesterified fatty acids as well as specific activity and gene expression of Met synthase and methylmalonyl-coenzyme A mutase in the liver. Ingestion of folic acid supplements by cows fed no supplementary B-12 increased total lipid and triacylglycerols in liver, whereas these supplements had no effect in cows supplemented with B-12. The increases in milk and milk protein yields due to folic acid supplements did not seem to be dependent on the vitamin B-12 supply. However, when vitamin B-12 was given in combination with folic acid, utilization of the 2 vitamins seems to be increased, probably more so in extrahepatic tissues. Metabolic efficiency seems also to be improved as suggested by similar lactational performance and dry matter intake for cows fed supplementary folic acid but increased plasma glucose and decreased hepatic lipids in cows fed folic acid and vitamin B-12 together.