Seasonal variation in serum testosterone, T3 and andrological parameters of two Turkish sheep breeds

Five Chios and five Daglic fat-tailed rams were used to study the effect of season on certain hormonal and andrological parameters for a period of 1 year. Semen and blood samples were collected monthly via the artificial vagina from rams to determine serum testosterone and triiodothyronine (T3) hormone concentrations. In spite of the large variation, most of the semen characteristics recorded between the breeds, seasonal variation in testes volume, semen quantity (semen volume and sperm concentration) and quality (sperm motility and abnormal sperm) were significant (P < 0.05). The most viable semen was produced during late summer and the early autumn months. Testes volume varied significantly between months (P < 0.01), and between breeds (P < 0.05). Ejaculate volume, sperm motility and sperm concentration were higher during the autumn than the other months of the year. In addition autumn showed a moderate incidence of abnormal sperm. Months of the year had a significant (P < 0.01) effect on the serum T3 and testosterone levels. The magnitude of these seasonal effects was not sufficient to prevent rams from being used for breeding throughout the year. The variation recorded between individual rams regarding certain andrological and seminal properties makes it necessary to perform a spermiogram to select fertile males before being used for breeding. © 2005 Elsevier B.V. All rights reserved.