ABSTRACT
The role of thyroid hormones has been recognized in normal embryo development many years ago. These hormones also affected the development of reproductive organs and their activity. This study was conducted to investigate the effect of inducing hypothyroidism by propyl-2-thiouracyl [PTU] on lambs testicular histomorphology and plasma testosterone concentration. Eighteen Lori-Bakhtari male lambs were divided to 3 groups [n=6] and each received one of the treatments as Control [C: 0 mg PTU/kg BW], Low [L: 10 mg PTU/kg BW] and High [H: 20 mg PTU/kg BW] by gavages, during a 60d experimental period. At the end of the trial, lambs were slaughtered and testes were removed to evaluate their histomorphological characteristics. Mean concentration of T4 and T3 decreased significantly in Land H groups compared with C group [p<0.05]. Hyphothyroidism increased testis weight, number of sertoli and lydig cells, diameter of Seminiferous tubules, diameter of seminiferous lumen, total spermatogonia, number of primary spermatocyte, and total spermatids [p<0.05]. However, PTU had no significant effect on plasma concentration of testosterone [p>0.05]. In the present study, PTU increased testicular weight and the number of cells involved in sperm and testosterone production. Sheep breeders may consider hypothyroidism as a potential approach to increase sperm production capacity in rams before puberty. However, further investigation should be carried out on the quality and quantity of rams' sperm