SERUM CLEARANCE AND URINARY-EXCRETION OF PTEROYLMONOGLUTAMIC ACID IN GESTATING AND LACTATING DAIRY-COWS

The present experiment was undertaken to verify if the demand of tissu es for pteroylglutamic (folic) acid, evaluated by serum clearance and urinary excretion of folates, is different between multiparous dairy c ows in late gestation (five gestating dry cows, 52.6 (so 8.4)d before parturition), and in early lactation (four lactating non-gestating cow s, 18.0 (so 5.9)d after parturition). On day 1 the cows received one i ntravenous (i.v.) injection of 50 mu g pteroylmonoglutamic acid/kg bod y weight (BW). Blood samples mere taken at 0, 5, 15, 30 min, 1, 2, 4, 8 and 24 h after the i.v. injection. On day 3 the cows received one in tramuscular (i.m.) injection of 0 3 mg pteroylmonoglutamic acid/kg BW. Blood and urine samples, as well as urine volume, were taken at 0, 1, 2, 4, 8, 12, 24, 36 and 48 h after the i.m. injection. On days 5, 6 a nd 7 a daily i.m. injection of 0 5 mg pteroylmonoglutamic acid/kg BW w as given in an attempt to saturate tissues with folates. Then the cows received one i.v. (day 8) and one i.m. (day 10) injection of pteroylm onoglutamic acid according to the same procedures described previously for days 1 and 3. On day 12 plasma volume was determined. Before tiss ue saturation, serum clearance of folates during the 24 h following an i.v. injection was similar for gestating and lactating cows but after tissue saturation serum clearance was slower for lactating than gesta ting cows (stage x saturation, P = 0.04). The percentage of folates ex creted in urine was not affected by the physiological stage (P greater than or equal to 0.6) or the level of tissue saturation (P greater th an or equal to 0.5). In conclusion, serum clearance and urinary excret ion of pteroylmonoglutamic acid seem to support the hypothesis that, i n multiparous cows, although there are no deficiency symptoms, tissue demand for folic acid is high, especially during gestation.