Serum and red cell folate and serum vitamin B12 levels in horses.

Vitamin B12 and folate concentrations were determined by radioimmunoassay in groups of horses in Queensland. Highest serum vitamin B12 levels were found in supplemented performance horses. These, together with pastured horses that included pregnant and lactating mares, had significantly greater serum folate activity than permanently stabled animals. The range of red cell folate concentrations was much narrower in horses in training than from any other group. Red cell folate may be a better indicator of a horse's folate status than the serum folate value. Vitamin B12 and folate concentrations were highest in spring and summer. Small intestinal dysfunction in 2 horses was not associated with vitamin B12 or folate malabsorption. Serum folate levels returned to normal 24 h after intramuscular injections of 75 to 150 mg folic acid, whereas serum vitamin B12 values remained elevated for at least one week following injections of 8 to 10 mg to non-supplemented horses. None of the horses in this survey had evidence of vitamin B12 or folate deficiency, or showed significant haematological changes. Nevertheless, permanently stabled horses and some horses in training may require additional folic acid, preferably on a daily basis by the oral route. However, exogenous vitamin B12 administration does not appear to be justified.