Postnatal testicular development and testosterone changes in Ghezel ram lambs

- Lumenization was began in the 4th month and then completed after 8 months of age.
- Spermatogenesis started when the spermatocyte cells were observed at 4 months of age.
- Leydig cells were observed at 4 month-old lambs.
- Leydig cell number showed a similar pattern as that observed for testosterone levels.

This study was conducted to investigate the histological structure of testis and hormonal changes during prepubertal Ghezel ram lambs. Histometrical evaluation of the testis was performed in 36 Ghezel lambs from one to 9 months of age. Lambs were allotted into nine groups, and surgically castrated each month from 1 to 9 months of age (n = 4 lambs per group). In addition, blood samples were taken from six animals from 1 month of age to adulthood to measure plasma levels of testosterone. With the age held constant, scrotal circumference and body weight were correlated (r = 0.960, P < 0.01). The sex cords did not have lumen up to the age of 4 months and lumenization process was completed after 8 months of age. A dramatic increase in spermatogonia cells per cross-section of seminiferous tubule was observed from 3 to 5 months of age; their number per tubule cross-section stabilized after 8 months. Spermatogenesis started when the spermatocyte cells were observed at the 4th month, and established at 8 months of age (body weight = 42.39 kg, scrotal circumference = 25.8 cm). Onset of puberty was observed to be established at 8 months of age when spermatozoa, adhered to the adluminal border of the Sertoli cells as well as in the tubular lumen. Leydig cells were visible in 4-month-old lambs. During the 5 months after birth, Leydig cell number showed a similar pattern as that observed for testosterone plasma levels. At 8-9 months of age the testosterone plasma level reached up to 2 ng/ml which contributed to the increase in testicular testosterone secreting capacity of the mature adult Leydig cells, with the accomplishment of this transition, sexual puberty is completed. It can be concluded that establishment of spermatogenesis begins a long time before puberty in 8 month-old Ghezel lambs.