Orotic Acid and Pyrimidine Nucleotides of Ruminant Milks

Abstract

Reports conflict on the apparent high content of orotic acid in ruminant milks compared to that (0 to 5μg/ml) in milks of other species and animal tissues. Amounts reported for mid-lactation ovine (sheep) milk and early lactation bovine (cow) milk range from none to over 320μg/ml based on chemical and microbiological assay procedures with the latter giving the higher results. To clarify this discrepancy, orotic acid in ovine and bovine milks was determined by a direct chemical and two microbiological assay procedures using mutant bacteria lacking different functional portions of the pyrimidine synthesis pathway before and after orotic acid. Nine mid-lactation ovine milks contained 26±9μg/ml of orotic acid and 331±51μg/ml (as uracil) of pyrimidines all of which were evaluated as orotic acid in the microbiological bioassay procedures showing a large amount. Bovine milks from early lactation were similar. Four bovine samples of first colostrum contained 21±7μg/ml of orotic acid and 279±96μg/ml (as uracil) of pyrimidines. Eight mid-lactation bovine milks contained 88±19μg/ml of orotic acid but only small amounts of pyrimidines. The orotic acid and pyrimidine contents of these milks interpreted from the chemical and microbiological assay procedures agree closely with those based on the isolation and separation of acid-soluble nucleotides. Pyrimidine nucleotides comprise 1 to 2% of the total nonfat solids of ovine milk with only relatively small amounts of orotic acid. In contrast, bovine milk contains only small.