The objective was to characterize testicular development in Blackbelly sheep, focusing
primarily on Sertoli cell number. Lambs (n=43) were allotted into eight groups, and
surgically castrated at 0, 3, 6, 9, 12, 15,18 or 21 weeks of age (n=4-6 lambs per
group). Testes were fixed and paraffin-embedded, cross-sections (5 microm) were stained
and evaluated with quantitative morphometry techniques. Testis weight increased at
a greater rate between 9 and 15 weeks of age, which was associated with remarkable
changes in testicular histology, including increases in tubular tissue volume, and
tubule diameter and length. Spermatogenesis started in a period between 9 and 12 weeks,
lumen and elongated spermatids were observed for the first time at 12 weeks (78% of
the tubules) and 15 weeks (37% of the tubules), respectively. Total number of Sertoli
cells (mean+/-S.E.M.) increased steadily from birth (531+/-76 x 10(6)) to 15 weeks
(12,008+/-1722 x 10(6)), with no changes afterwards. Sertoli cell number per gram
of testicular tissue decreased as lambs were older, with the most remarkable change
occurring between Weeks 9 and 12. An early increase in serum LH was observed at 6
weeks of age, with testosterone (T) increasing at Weeks 12 and 21. In conclusion,
Sertoli cells maintained the capacity of proliferating from birth to 15 weeks of age
in Blackbelly sheep; furthermore, the period of accelerated testis growth was associated
with increased serum T concentration and with important changes in testicular morphology,
as a consequence of the beginning and establishment of spermatogenesis and Sertoli
cell maturation.