ONSET OF SPERMATOGENESIS IN CORRIEDALE RAM LAMBS UNDER EXTENSIVE REARING CONDITIONS IN URUGUAY

The present study was undertaken to estimate the time for the attainme nt of spermatogenesis in spring-born Corriedale ram lambs under condit ions of extensive grazing systems in Uruguay. Clinical (live weight, s crotal circumference, penile/preputial separation), morphological(ligh t and electron microscopy) and endocrinological (testosterone levels) parameters were examined. Two experiments in 2 consecutive years were carried out. In Exp. I, 40 ram lambs were clinically examined, weighed , and blood-sampled at 2 week-intervals between 78 and 216 days of age . Sixteeen were castrated in 3 selected periods: 132-162 (n: 2), 145-1 75 (n: 6) and 186-216 days (n: 8). In Exp. II, 40 ram lambs appertaini ng to the next generation of the same flock were examined as above at 180-210 days of age, and castrated for morphological studies. The time for attainment of complete spermatogenesis correlated significantly w ith most corporal parameters (i.e. scrotal circumference (r = 0.52); t esticular weight (r = 0.61), epididymal weight (r = 0.60), penile/prep utial separation (r = 0.75). The age of castrated ram lambs correlated with the degree of spermatogenesis (r = 0.83), although no significan t correlations were found with live weight or with levels of circulati ng testosterone. The histology showed major variations in the degree o f development of the seminiferous epithelium. Cells undergoing degener ation were a common finding through the initial stages of spermatogene sis, coincident to the presence of sperm abnormalities and foreign cel ls in semen. By day 180 and onwards, both histology and seminal pictur e normalized. It is concluded that, under these rearing conditions, th e onset of puberty (expressed as morphologically established spermatog enesis) in Corriedale ram lambs is attained at 180-216 days of age whe n they reach 23 cm of scrotal circumference and 191 g of testis weight . The finding of a high correlation between these parameters (r: 0.93) confirms the usefulness of the measurement of scrotal circumference d uring clinical examination of ram lambs in this breed.