Detection and prevalence of UMP synthase deficiency among dairy cattle.

A partial deficiency of UMP synthase has been detected in Holstein dairy cattle. Since affected females secrete milk with elevated concentrations of orotate, milk orotate was used to screen for the condition among 880 cows in 17 randomly selected Holstein herds in Illinois. Mean orotate was 85.0 +/- 1.5 microgram/ml milk and 17 cows had milk orotate in excess of 170 micrograms/ml. Including the latter animals, 42 cows were evaluated for erythrocyte UMP synthase and 15 were found to be partially deficient. Thus, at least 1.7 percent of all cows had the condition; this is a minimal estimate because the initial screen was milk orotate and this may be low, particularly early in lactation. Deficient cows had half the level of UMP synthase as normal, nondeficient cows (1.30 +/- 0.06 vs. 2.79 +/- 0.10 units/ml). The binomial classification of deficient versus normal accounted for 72 percent of the variation noted in UMP synthase. Milk orotate was significantly elevated in deficient cows (337.8 +/- 31.3 micrograms/ml), validating its use as a screening device. Urinary orotate also was higher for deficient cows (28.4 +/- 5.2 vs. 9.2 +/- 0.8 micrograms/ml) and differentiated the two groups as well as milk orotate. Normal and deficient cows did not differ in milk lactose concentrations. Erythrocyte UMP synthase also was measured in 85 Holstein bulls used for artificial insemination and 6 had low levels of UMP synthase (1.39 +/- 0.19 vs. 2.92 +/- 0.05 units/ml); the binomial classification accounted for 42 percent of the variation. The partially deficient animals identified appear to be heterozygotes for a condition expected to be lethal in the homozygous state.