RESUMEN
Whether paired organs are equivalent has to be analyzed by assessing both structural and functional aspects. The present study compared the paired left and right testis from Ghezel sheep originating from Northwestern Iran (Azerbaijan) and Northeastern Turkey. Twenty-five pairs of testes were collected from mature Ghezel rams from Tabriz slaughterhouse. The two glands were compared for their size, weight and activity rate. Weight, length, width and thickness were measured. Then, paraffinized blocks were prepared by routine histological techniques and sections were stained by the haematoxylin-eosin method. Five 6 µm sections were prepared from each paraffinized block and 50 seminiferous tubules (STs) were analysed in each section for tubular differential index (TDI) and spermiogenesis index (SPI). TDI and SPI were compared between the paired left and right testes. Weight, length and thickness of left testes were significantly higher than in right testes (P < 0.05). Moreover, TDI and SPI were found to be higher in left testes than the right (P < 0.05).