Effects of Dietary Supplements of Folic Acid and Vitamin B_(12) on Metabolism of Dairy Cows in Early Lactation

摘要

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 mul-tiparous 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 homocys-teine, 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 methylmalonyl-coenzyme 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.