Incidence and inheritance of deficiency for uridine monophosphate synthase in Holstein bulls

A partial deficiency of uridine monophosphate synthase has been discovered among Holstein dairy cattle wherein affected animals have half the normal activity of this enzyme and are heterozygous for a condition presumed to be lethal in the homozygous recessive state. A random sample of 287 dairy bulls, active in artificial insemination organizations, were assayed for their activity of uridine monophosphate synthase. Four bulls displayed reduced enzyme activity (heterozygotes) corresponding to a 1.4% incidence and were closely related to a common ancestor, Bull-X. Testing a total of 75 male descendants of Bull-X has uncovered 22 heterozygotes. Heterozygotes include 5 sons, 15 grandsons, 1 a double grandson, and 2 great grandsons of Bull-X. Reproductive failure from this enzyme deficiency has been minimal because matings between close relatives have been infrequent. If the incidence of heterozygotes active in artificial insemination increases, avoidance of matings between close relatives will become an inadequate safety measure to maintain reproductive fitness. Random mating of male heterozygotes to a female population with 2% incidence of heterozygotes may imply an additional .5% embryonic loss relative to matings involving bulls that are normal for uridine monophosphate synthase.