Changes in serum concentrations of folates, pyridoxal, pyridoxal-5-phosphate and vitamin B12 during lactation of dairy cows fed dietary supplements of folic acid

The present experiment was undertaken to determine the effects of dietary supplements of folic acid (FA) administered from 4 wk prepartum to 305 d of lactation on serum concentrations of folates, vitamin B(12), pyridoxal-5-phosphate (P-5-P) and pyridoxal. In addition, concentrations of blood hemoglobin and packed cell volume (PCV) were determined. Sixty-three Holstein cows were assigned to 22 incomplete blocks according to lactation number, milk production and body weight (BW). Within each block, cows received 0, 2 and 4 mg FA d(-1) kg(-1) BW. Dietary supplements of FA increased serum concentrations of folates (time x FA, P = 0.0001); the highest concentrations were observed during the first two months of lactation in cows fed supplementary FA. The lowest serum concentrations of vitamin B(12) were also observed during the first two months of lactation, and the concentrations were lower in primiparous than in multiparous cows (time x parity, P = 0.03). Serum concentrations of P-5-P and pyridoxal were not affected by the dietary supplements of FA (P > 0.1). In multiparous cows, dietary supplements of FA had no effect on changes of hemoglobin and PCV during the lactation (time x FA, P > 0.13). In primiparous cows, PCV and hemoglobin were lower in control cows at parturition whereas by 24 wk of lactation, they were higher in cows fed the highest amount of FA. The lowest values of hemoglobin and PCV were observed during the first two months of lactation. These results give an indication that supply of B-complex vitamins by ruminal microorganisms could be suboptimal for high-producing dairy cows, for example, in early lactation when fed a diet with a high proportion of concentrates. More research is needed to determine the metabolic consequences of these variations.