Folic Acid in Ruminant Nutrition

Folic acid plays an essential role in ruminant nutrition. Microorganisms in the rumen can synthesise folates, but these amounts are not sufficient to achieve the best efficiency of dairy cows. However, the amount of folates synthesised in the rumen could possibly, to some extent, be affected by the forage: concentrate ratio. The supply of folates by the diet and the synthesis by ruminalmicroflora is sufficient to prevent folic acid deficiency in dairy cows and to maintain normal gestation and lactation. Degradation of orally supplemented folic acid in the rumen seems to be very high (about 97 %), as supplementation of folic acid hardly increases folate concentrations in the digesta at the duodenum. However, it must be considered that dietary supplements of folic acid higher than 0·5 mg/kg body weight increased serum folate concentrations in all available studies and milk folate concentrations in most studies. Additionally, milk production tended to be increased in some studies. Therefore, degradation of folic acid in the rumen may be overestimated as folates can be absorbed at the proximal duodenum. For future research it is necessary to consider the whole flow and the metabolic pathways of folates from the rumen to duodenum, blood, tissue, milk and transfer to calf to declare requirement values for cows.