SERUM CLEARANCE AND URINARY-EXCRETION OF FOLIC-ACID IN MILK-FED AND WEANED CALVES

Thirty male calves were assigned to treatments in a 2 x 3 factorial ex periment in which the diet (exclusively milk replacers or dry feed) an d 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 t he two main factors. During their first 4 mo of life, the folate statu s of calves was evaluated monthly. In milk-fed calves, erythrocyte con centration of folates increased with the duration of the supplementati on (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 supplementatio n but it was higher for those receiving the long-term supplementation and the decrease with age was more marked with this last treatment (su pplementation x age, P = 0.01). Serum clearance of an i.v, bolus of fo lic 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 o f 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 w eaned 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.