Serum folates in gestating and lactating dairy cows.
In Experiment 1, 70 cows were distributed in five groups of 14 animals each. Each group represented one physiological stage: parturition, 2 mo postpartum, 3 mo of gestation, 6 mo of gestation, and drying off at approximately 2 mo before parturition. Plasma volume, concentration of serum folates, and total serum folates were measured at each stage. In Experiment 2, four doses of folic acid (40, 80, 160, and 320 mg) were administered by intramuscular injection to four groups of 5 cows in late gestation and four groups of 5 cows in early lactation. Serum folates in all cows and milk folates in lactating cows were determined before injection of folic acid and on d 1, 2, 4, 8, and 16 after injection. In Experiment 1, plasma volume did not differ between physiological stages, but total serum folates increased from parturition to reach a peak value 2 mo later; thereafter, serum folates decreased from 3 mo of gestation to parturition. In Experiment 2, during late gestation, serum folates increased after injection of folic acid and reached the highest concentration with the dose of 160 mg. However, during early lactation, injection of folic acid had no effect on concentrations of serum or milk folates. Therefore, total serum folates decreased by 40% from 2 mo postpartum (around mating) to parturition. Moreover, at the end of gestation, serum folates can be increased by an intramuscular injection of folic acid. This may be an indication of an increased need for folic acid during gestation of dairy cows.