Changes in serum concentrations of folates, pyridoxal, pyridoxal-5-phosphate and vitamin B-12 during lactation of dairy cows fed dietary supplements of folic acid

The present experiment was undertaken to determine the effects of dietary s upplements of folic acid (FA) administered from 4 wk prepartum to 305 d of lactation on serum concentrations of folates, vitamin B-12, pyridoxal-5-pho sphate (P-5-P) and pyridoxal. In addition, concentrations of blood hemoglob in and packed cell volume (PCV) were determined. Sixty-three Holstein cows were assigned to 22 incomplete blocks according to lactation number, milk p roduction 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 concentra tions of folates (time x FA, P = 0.0001); the highest concentrations were o bserved during the first two months of lactation in cows fed supplementary FA. The lowest serum concentrations of vitamin B-12 were also observed duri ng the first two months of lactation, and the concentrations were lower in primiparous than in multiparous cows (time x parity, P = 0.03). Serum conce ntrations of P-5-P and pyridoxal were not affected by the dietary supplemen ts of FA (P > 0.1). In multiparous cows, dietary supplements of FA had no e ffect 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 obse rved during the first two months of lactation. These results give an indica tion that supply of B-complex vitamins by ruminal microorganisms could be s uboptimal for high-producing dairy cows, for example, in early lactation wh en fed a diet with a high proportion of concentrates. More research is need ed to determine the metabolic consequences of these variations.