Serum clearance and urinary excretion of folic acid in milk-fed and weaned calves

Thirty male calves were assigned to treatments in a 2 × 3 factorial experiment in which the diet (exclusively milk replacers or dry feed) and the duration of the period of folic acid supplementation (no, short-term, i.e., 7 d before each period of evaluation of the folate status, or long-term supplementation, i.e., throughout the experiment) were the two main factors. During their first 4 mo of life, the folate status of calves was evaluated monthly. In milk-fed calves, erythrocyte concentration of folates increased with the duration of the supplementation (P = 0.008) but it decreased with age (P = 0.01). In weaned calves, it was similar for calves receiving no or a short-term supplementation but it was higher for those receiving the long-term supplementation and the decrease with age was more marked with this last treatment (supplementation × age, P = 0.01). Serum clearance of an i.v. bolus of folic acid was similar for milk-fed and weaned calves (P = 0.2), it was more rapid with age (P = 0.02), but it slowed down with the duration of the supplementation (P = 0.05). The percentage of the dose of folic acid injected i.m. recovered in urine was higher in milk-fed than in weaned calves (P = 0.0001) and it decreased with age (P = 0.0001). The present results suggest that the tissue demand for folic acid is high in preruminant and ruminant calves and it increases during the first 4 mo of life. Key words: Folic acid, serum clearance, urinary excretion, milk-fed calf, weaned calf