Luteinizing Hormone and Testosterone Concentrations in Plasma of Bull Calves Treated with Gonadotropin Releasing Hormone

Abstract

Twelve bull calves, 2 to 24 days of age, were assigned to two groups of six calves and administered a single 50 μg intramuscular injection of gonadotropin releasing hormone. Bull calves in group 1 were 2 to 5 days of age (mean 3.0 days), and bull calves in group 2 were 10 to 24 days of age (mean 17.1 days). Blood plasma for radioimmunoassay of luteinizing hormone and testosterone was collected at .5-h intervals for 3-h and at 4- and 6-h following treatment. With increasing age, preinjection luteinizing hormone concentrations in plasma decreased while preinjection testosterone concentrations increased. Mean preinjection luteinizing hormone concentrations for group 1 (1.01 ± .07 ng/ml; mean ± standard error) were higher than for group 2 (.61 ± .12 ng/ml). Preinjection luteinizing hormone and testosterone concentrations were correlated −.63. Following treatment, luteinizing hormone increased with mean peak concentrations of 7.28 ± .74 and 6.95 ± 1.79 ng/ml for groups 1 and 2. Peak testosterone response following gonadotropin releasing hormone was higher for group 2 than 1 (1077 ± 253 versus 436 ± 116pg/ml). © 1977, American Dairy Science Association. All rights reserved.