Seasonal variation of sex hormones and semen quality in Simental bulls

The purpose of this study was to find out whether the seasonal climate changes have any impact on sex hormones levels and semen characteristics in Simmental bulls kept in the insemination station. The study was conducted for a year. Ejaculates of twelve bulls were collected from each bull three times a month using an artificial vagina. Basic semen characteristics - ejaculate volume, sperm concentration, motility, and percentage of live sperm - were assessed in the collected samples. Blood was drawn monthly from the bulls to measure testosterone and estradiol levels. Significant differences were found in the levels of sex hormones in blood serum and in the bull sperm depending on the season. The highest testosterone levels were observed in summer, while estradiol levels in spring. Semen concentration was best in summer, motility in spring and viability in autumn. There was no clear relationship between hormone levels and semen parameters. The obtained results suggest that season has a large impact on the serum testosterone and estradiol levels and also on bovine sperm parameters.