Concentrations of folates in ruminal content of steers: responses to a dietary supplement of folic acid in relation with the nature of the diet.

In an attempt to evaluate the ruminal effects of dietary supplements of folic acid, eight steers (352 +/- 27 kg BW) fitted with a ruminal cannula were randomly assigned to a replicated 4 x 4 Latin square design. The treatments were 70% rolled barley + 30% timothy hay (HC), HC + 2 mg of folic acid per kilogram of BW (HC + FA), 30% rolled barley + 70% timothy hay (HF), and HF + 2 mg of folic acid per kilogram of BW (HF + FA). After 5 wk of adaptation to the dietary treatments, ruminal contents were sampled over three consecutive days, at 1, 2, 4, 8, 12, and 23 h after feed distribution. Concentrations of folates in solid and liquid ruminal fractions were increased by the dietary supplement of folic acid (P = .0001) and by the ingestion of concentrate compared with hay-based diets (P < .05). Preprandial concentrations of serum folates were not affected by the nature of the diet when steers received no folic acid but the increase of serum folates induced by the dietary supplement of folic acid was more important in steers fed concentrates than in those fed hay-based diets (diet x supplement of folic acid interaction P = .002). Microbial protein (P = .004) and microbial mass (P = .002) in ruminal fluid were increased with concentrate-based diets compared with hay-based diets; folic acid did not have any effect on these variables (P > .05). In conclusion, concentrations of folates in ruminal contents were affected by dietary supplements of folic acid and by the nature of the diet.(ABSTRACT TRUNCATED AT 250 WORDS)