Improved Semen Characteristics in Boars Selected for Testis Size

The practice of artificial insemination is increasing in swine herds. There is considerable variation among boars in age when semen can be collected, volume of semen, and sperm concentration, motility of sperm cells, and frequency of abnormalities in semen. Selection of boars has been for performance traits such as growth rate and backfat thickness and female reproductive traits such as size and weight of litters of dams and other female relatives. Little selection for male reproductive traits has been practiced. However, selection practices that result in boars with greater quantities of high quality semen would improve the efficiency of artificial insemination and be beneficial to the industry. Testis size is correlated with daily sperm production and with total sperm numbers in the epididymis in several species, including swine. At Nebraska, an experiment was conducted in which selection for increased weight of testes at 150 days of age (TS line) was practiced. A randomly selected line (control, C line) was also maintained for 10 generations. The purpose of this article is to report results of an experiment which evaluated differences in quantity and quality of semen produced by boars of the TS and C lines