Vitamin B12 is produced in a cow’s rumen by microbes and is essential for normal red blood cell formation.
Rumen microorganisms synthesize vitamin B12, also known as cobalamin, when adequate cobalt is available in the diet. The vitamin is later absorbed mainly in the small intestine after digesta passes through the rest of the digestive tract.
Vitamin B12 supports DNA synthesis, red blood cell production, and normal nervous-system function. Cobalt deficiency can therefore cause poor growth, anemia-like signs, and reduced productivity even when forage appears plentiful.
Cattle do not manufacture B12 with their own tissues; their microbial community does the work. This is one example of the close nutritional partnership created by ruminant digestion. Vitamin B12 is different from vitamin K, which rumen microbes can also produce, but whose functions are not the same.