Repeatability of scrotal size and semen quality measurements in rams in a short-day light regime

Abstract Adult rams were exposed to 16 h light daily for 3 months and then to 8 h light daily (short days) for 3 years to study the long term effects of short days on testis size and semen quality. Every 2 weeks, scrotal circumference was measured and semen collected and evaluated. Scrotal size increased ( P R = 0.85). Semen quality measures showed lower repeatability estimates: ejaculate volume, 0.62; sperm number per ejaculate, 0.50; sperm concentration, 0.35; percent motile sperm, 0.33 and progressive sperm motility, 0.26. Biweekly scrotal measurements were poorly correlated with semen quality, within rams. The findings indicate that continual exposure of rams to short days maintains testicular size and function at near-maximal levels and scrotal measurements become highly repeatable. Under these conditions, scrotal size may be a useful index of sperm production among rams.