Clinical deficiencies in B vitamins are extremely rare in dairy cows under normal feeding conditions because the ruminal microbiota synthesizes these vitamins. Nevertheless, improvement in lactation performance following B-vitamin supplementations suggests subclinical deficiencies which reduce metabolic efficiency. Even when cows are fed diets adequately balanced for energy and major nutrients, the need for these vitamins can sometimes exceed the supply from the diet and the synthesis by the rumen microbiota, especially in early lactation, when dry matter intake is low.
Due to their metabolic roles and interdependence, folic acid, and vitamin B12 are two B vitamins of interest for dairy cows. Folates, the biologically active forms of folic acid, provide one-carbon units for DNA synthesis affecting cell division for fetal and mammary development. Both vitamins, folates and vitamin B12, are critical for de novo synthesis of methyl groups for methylation of DNA, controlling gene expression, and methylation of phosphatidylethanolamine to generate phosphatidylcholine, the major phospholipid in membranes and lipoproteins.
Vitamin B12 also acts as a coenzyme in propionate metabolism, the primary source of glucose in dairy cows. The efficiency of folate and vitamin B12 metabolism depends on an adequate supply of both vitamins. On one hand, a lack of vitamin B12, even in the presence of an adequate folate supply, blocks the utilization of folates for DNA synthesis. On the other hand, a low folate supply interferes with the utilization of vitamin B12 for propionate metabolism.
A survey of the scientific literature shows that a supplement of folic acid alone or combined with vitamin B12 increased or tended to increase yields of milk or energy-corrected milk in 14 out of 19 experiments and increased or tended to increase milk protein concentration in 8 experiments during early and mid-lactation. Milk yields of fat and protein followed a pattern similar to milk yield. Except for one experiment, the increase in milk, energy-corrected milk, or milk component yields observed with the vitamin supplementation changed neither dry matter intake nor body weight.
In some experiments, the supplements in early lactation decreased body weight or body condition loss. The improved lactation performance without increasing dry matter intake or mobilization of body reserves indicates that folic acid and vitamin B12 supplements, especially when given together, improve energy ...
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