Control of Sertoli and germ cell populations in the cock and sheep testes.

Sertoli cells are involved in the control of spermatogenesis. In adult animals, the Sertoli cell stocks, fixed before puberty, are highly correlated with those of the germ cells. Some factors influencing Sertoli cell stock formation have been analyzed: 1) Early hemicastration of impuberal animals showed that the proliferative activities of the Sertoli and the germ cells before puberty, rather than their initial numbers at birth, were the limiting factors of their final number in adult testis. 2) During testicular growth, LH and FSH levels were correlated to Sertoli cell stocks and to germ cell production. 3) The season of birth influenced the Sertoli cell stock formation in the ram. Daylength modified testicular development in the cockerel and the sheep. 4) Between-strain differences were more marked for the testis than for body growth in the cockerel. In the ram, Sertoli cell stocks were similar between half-brothers but significantly different between sires.