Reduced male reproductive capacity in mice with high genetic potential for post-weaning growth

Male reproductive capacity was examined in 5 lines of mice which differed markedly in mature body weight (30-73 g) due to selection for growth and/or substitution of the high growth gene (hg). Testes weight ranged from 0.75-0.77% of body weight in control lines to 0.33% in the largest mice which had the hg gene in a growth selected background. Both selection for growth and the hg gene in a control background reduced absolute testes size (0.200 and 0.207 g vs 0.236 and 0.228 g in control lines) as well as relative testes size although body weight was increased by at least 50%. Although the combination of growth background and hg gene reduced sperm production per g testis compared to the outbred control, the primary cause of reduced sperm production per mouse in lines containing either the growth background or the hg gene alone was reduced absolute testes size. At 24, but not at 11, weeks of age, the hg gene reduced sperm motility. In these lines, high genetic potential for post-weaning growth was associated with decreased male reproductive capacity.