PLASMA LEVELS OF TESTOSTERONE IN BULLS

Abstract

Administration of 6000 IU HCG [human chorionic gonadotropin] to 4 bulls was followed by an elevation of plasma testosterone lasting for 9-13 days. When HCG administration was repeated, the testosterone response was shortened to 4-6 days in 3 bulls due to the formation of antibodies against HCG. The appearance of HCG antibodies coincided with a sharp decrease in the plasma testosterone level, indicating that Leydig cells have to be under continuous HCG stimulation to maintain increased testosterone production. No antibody against bovine LH [luteinizing hormone] was detected in the plasma samples containing antibodies against HCG. In one bull the response following the second HCG injection was similar to the plasma testosterone pattern following the 1st. No antibodies against HCG were found in this bull. Five bulls received 750 IU HCG twice. Following the period with elevated plasma testosterone levels, subnormal levels were observed after both injections. One injection led to decreased levels without development of antibodies against HCG while the 2nd HCG injection led to subnormal testosterone levels concomitant with measurable antibodies against HCG.