Bovine Milk Orotic Acid: Variability and Significance for Human Nutrition

Bovine milk, the main source of orotic acid in the human diet, contains approximately 80ng orotic acid per milliliter, .1% of the fat-free solids. Orotic acid is virtually the only component in the acid-soluble nucleotide fraction of bovine milk. Variation is considerable in the concentration of orotic acid from dairy cows. This is primarily attributable to cow-to-cow variation. A secondary factor is stage of lactation; orotic acid is low in colostrum, increases for 10 wk, and remains constant through most of the rest of lactation; upon cessation of milking, orotic acid in lacteal secretions decrease within 6 wk to the low content of colostrum. Orotic acid at 1% in the diet leads to severely fatty livers in rats; more than .1% is necessary to induce the effect. Furthermore, rats appear to be unique in their susceptibility to fatty livers induced by orotic acid. Mice, guinea pigs, hamsters, chicks, dogs, pigs, and monkeys do not respond similarly to diets with 1% orotic acid. The lack of susceptibility in mice is in part due to increased urinary excretion of dietary orotic acid. The basis for the absence of response in other species has not been examined. While research is required, the evidence does not suggest that orotic acid in milk poses a serious problem to human consumers.