Folic acid and vitamin B12 requirements of dairy cows: A concept to be revised

Based on a limited number of research studies conducted on steers, it seems that the supply in folic acid could be limiting based on estimated ruminal synthesis and dietary supply. Folic acid has the single, important biochemical function in mammals to accept and release one-carbon units. This role is essential for the synthesis of purine and pyrimidine and the de novo provision of methyl groups for formation of the primary methylating agent, S-adenosylmethionine. Given its metabolic roles, folic acid is critical for cell division and protein metabolism, and therefore is an ideal candidate to begin with while reviewing B-vitamin requirements of dairy cow for an optimal productivity. Moreover, metabolisms of folic acid and vitamin B₁₂ are closely linked, utilization of folates by cells being dependent of vitamin B₁₂ supply. Studies reported in the present paper demonstrate that the supply in these two B-vitamins is not always sufficient to maximize health and productivity of dairy cows. Supplementation in those vitamins, especially during early lactation, improved lactational performance, metabolic efficiency and nutritional quality of milk. However, other research needs to be conducted to overcome the problems caused by the massive destruction of dietary supplements of those vitamins in rumen.