Investigations on the influence of prolactin suppression on reproductive function in bulls

In 3 mature bulls 2 injections (i.m.) of 150 mg 2-Br-alpha-ergocryptine (CB-154, Sandoz) within 48 hrs. decreased the plasma prolactin concentrations significantly for about 14 days (first experiment). In a second experiment, where treatment was repeated after 2 weeks, the period of maximal prolaction deficiency could be extended to a length of about 4 weeks. However, intensity of prolactin inhibition was less pronounced. This is attributed to seasonal factors. Neither during the shorter nor during the longer period of prolactin suppression were apparent changes of the LH and testosterone levels observed. Apart from a minor increase in the rate of morphologically abnormal sperm cells, reproductive function as libido, mating behaviour, semen quality, secretory activity of the accessory glands (concentration of fructose, GPC and chloride in seminal plasma and pre-sperm fraction resp.) were not significantly affected. It seems questionable, therefore, whether under physiological conditions prolactin is essential for the regulation of sexual functions in mature bulls.