Influence of age, sex, lactational state and exogenous growth hormone on erythrocyte UMP synthase in dairy cattle

Abstract 1. 1. UMP synthase activity was determined in erythrocytes of Holstein cattle to assess differences attributable to age, sex, lactational state, and exogenous growth hormone. 2. 2. Newborns had 80% more UMP synthase activity per ml erythrocytes than mature cattle. 3. 3. Males had 10% more UMP synthase activity than females of the same age. 4. 4. Lactating and non-lactating mature females did not differ in UMP synthase activity. 5. 5. Over the first six weeks of life, the decrease in UMP synthase activity was less pronounced in calves partially deficient for the enzyme. 6. 6. Ten daily injections of growth hormone altered neither UMP synthase activity in erythrocytes nor orotic acid concentrations in milk and urine.