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Xanthine Oxidase Polymorphism in Bovine Milk^1,2,

Department of Animal Science and Biochemistry, University of Delaware, Newark 19711

ABSTRACT

The biological activity of xanthine oxidase (XO) was determined polarographically in situ in milk from 92 Guernseys and 39 Holsteins. Individual assays of the milk from each breed formed three nonoverlapping distributions. Means and standard errors for Guernsey milk based on 21 animals with low XO activity, 50 animals with medium XO activity, and 21 animals with high XO activity were 30 ± 0.9, 52 ± 0.9, and 80 ± 1.5 µliters O₂ per ml milk per hr. Corresponding XO activities for Holstein milk from 8 low XO activity, 20 medium XO activity, and 11 high XO activity animals were 28 ± 2.4, 48 ± 1.9, and 75 ± 2.1 µliters O₂ per ml milk per hour. A nonsignificant interaction between the sires and the activity of their daughters was found. However, results with the daughters of five sires representing 48 of the 81 animals suggested that the two alleles present are not random; they depend upon the genotype of the parents. Genetic polymorphism of the gene responsible for this enzyme with two alleles showing no dominance and additive gene action is proposed with the following nomenclature: high activity allele XO^A; low activity allele XO^B. Gene frequencies are: Guernsey, XO^A = 0.50; XO^B = 0.50, se ± 0.037; Holstein, XO^A = 0.54; XO^B = 0.46, se ± 0.058.

¹ Published with the approval of the Director of the Delaware Agricultural Experimental Station as Miscellaneous Paper 616, Contribution 5, of the Department of Animal Science and Biochemistry, University of Delaware, Newark.

² Data for this paper are from dissertation submitted by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biological Sciences, University of Delaware, 1970.