Quantifying the effect of seasonality on testicular function of Suffolk ram in lower latitude

Suffolk breed is known to display a clear seasonal reproductive response orchestrated by the significant annual variation in photoperiod related to its latitude of origin. However, in the low latitudes of the tropical and subtropical environments the magnitude and timing of these responses in Suffolk rams has been poorly investigated. This study aimed to quantify changes on andrological parameters in Suffolk rams kept under natural light/dark cycle and climate in the south of Brazil (25°25′40′′ S, 49°16′23′′ W). Rams were monitored during 1 year for testicular size, seminal parameters and serum testosterone. From autumn to winter, under shortening daylength, rams underwent a significant gonadal involution. Testicular size increased in spring and reached a peak in summer, similar to the latitude of which this breed originates. Parallel to scrotal circumference, other parameters such as testicular volume, serum testosterone concentration, ejaculate volume and sperm concentration followed a seasonal profile. Testosterone levels followed the same seasonal pattern as testicular size. Ejaculate volume was significantly lower during autumn and winter and higher values of sperm concentration were detected in spring. Furthermore, there were no significant changes in spermatozoa defects, motility, weave motion or vigor between seasons. In this paper we analyze the impact of seasonality over testis function in Suffolk rams at lower latitudes.