EFFECT OF FOLIC-ACID SUPPLEMENTATION ON FOLATE STATUS AND FORMATE OXIDATION RATE IN MINK (MUSTELA VISION)

We investigated the folate-dependent toxicity of formate to mink to be tter understand the use of formic acid in fur animal feeds. Folic acid supplementation (0, 1, 5, 10, and 20 mg/kg of DM) in the feed of wean ling mink for 4 wk resulted in hepatic tetrahydrofolate (H(4)folate) c oncentrations of 3.94, 8.51, 9.15, 10.4, and 15.0 nmol/g, respectively (SE 1.03). Oxidation tests in metabolic chambers, preceeding a single injection of sodium [C-14]formate (500 mg/kg BW), showed that the non supplemented mink oxidized formate into CO2 at a rate 37% less than th at of the supplemented mink. The oxidation rate increased with supplem entation level and was maximal, 54.2 mEq.kg(1).h(1) (SE 3.0), at 10 mg of folate/kg; at the highest level of supplementation (20 mg/kg), CO2 production tended to be lower. Concentration of hepatic C-14 increase d with the hepatic H(4)folate, and its accumulation continued after th e highest point of oxidation. These observations indicate that mink ox idize formate readily but at a slightly lower rate than do rats. Howev er, if extra folate is not supplemented in the feed during the period of early intensive growth, hepatic H(4)folate level may decline to the levels found in humans and monkeys, which are susceptible to formate accumulation. Average daily weight gain improved with each increase in supplementation of folic acid; however, only the differences between the nonsupplemented diet and the two highest levels of the vitamin rea ched statistical significance (P < .05).