Milk fat as related to vitamin B12 status

Two experiments examined whether vitamin B12 status of liver affects milk fat percentage or yield. In Experiment 1 B12 concentration in liver, measured at approximately 8 and 15 wk postpartum in 35 cows, was not correlated significantly with milk fat percentage or yield. In Experiment 2 twenty-two cows were fed a ratio similar to one used to depress milk fat percentage. The B12 status of 12 of these cows was enhanced by intramuscular injection of vitamin B12 while the other 10 served as controls. During wk 2 to 8 of lactation, milk fat percentages were almost identical for the two groups. A difference in milk fat yield in favor of the B12-treated group resulted from a difference in milk yield. The data do not support a recent hypothesis of the metabolic cause of milk fat depression.