Serum testosterone and estrogen concentrations in the Holstein-Friesian bull after successive ejaculations.

The testosterone and estrogen concentrations in venous serum of 4 mature Holstein-Friesian bulls were determined by radioimmunoassay before and after each of 3 consecutive semen collections taken at 1-hour intervals. The hormonal concentrations were highly variable for the 2 steroids, but uniform in their patterns after the bulls had ejaculated. After the 3rd semen collection, marked changes in hormonal concentrations did not occur.