In rabbits, intravenous injection of xanthine oxidase from bovine milk did not deplete arterial or coronary tissue plasmalogens, and did not induce arterial plaque formation. We, of course, are not rabbits and it's an old study.
Probable role of the enzyme in milk is itís
antibacterial activity by virtue of itís ability to produce oxygen derived free radicals. Oxy free radicals produced by the action of xanthine oxidase, in turn, oxidize cellular proteins and membranes resulting in myocardial cellular injury.