Seasonal variations in sexual behavior, testosterone, testicular size and semen characteristics, as affected by social dominance, of tropical hair rams (Ovis aries)

Abstract

The purpose of this study was to examine the effect of day length on seminal characteristics, testicular size, sexual behavior and testosterone concentration (T4) in dominant and subordinate Pelibuey rams. Six groups of three animals were evaluated every 2 weeks over a 12 month period. Dominant (D), medium (M) and subordinate (S) animals in each group were identified through a food competition test every 15 days. All rams ejaculated and produced semen throughout the year. A linear hierarchy was clearly established and maintained during the year. S rams had lower levels (P < 0.05) of semen volume, sperm concentration and testicular volume than D rams, regardless of season. Scrotal circumference was not influenced (P > 0.05) by their social position. D rams were more affected by the photoperiod, decreasing (P < 0.05) reaction times, increasing (P < 0.05) T-4 and producing more (P < 0.05) sperm per ejaculation than S rams during short days (14.65 +/- 1.22 vs 26.92 +/- 1.65 s

8.68 +/- 0.44 vs 7.37 +/- 0.40 ng/mL and 3.37 +/- 0.17 vs 2.04 +/- 0.16 sperm/10(9), respectively). Semen volume and sperm concentration were significantly (P < 0.05) greater during short days in all rams, regardless of their social status, with the exception of sperm concentration in D rams where no variation was found. M rams displayed variable values in the range between the D and S rams. It was concluded that the magnitude of the seasonal effects was not sufficient to prevent the rams being used for breeding throughout the year and that seasonal variation within the variables affected the social ranks differently.