INCREASED GERM-CELL DEGENERATION AND REDUCED GERM-CELL - SERTOLI-CELLRATIO IN STALLIONS WITH LOW SPERM PRODUCTION

To determine the relationship between germ cell degeneration or germ c ell:Sertoli cell ratio and daily sperm production, testes were obtaine d during the months of May to July (breeding season) and November to J anuary (nonbreeding season) from adult (4 to 20-yr-old) stallions with either high (n = 15) or low (n = 15) sperm production. Serum was assa yed for concentrations of LH, FSH and testosterone. Testes were assaye d for testosterone content and for the number of elongated spermatids, after which parenchymal samples were prepared for histologic assessme nt. Using morphometric procedures, the types and numbers of spermatogo nia, germ cells and Sertoli cells were determined. High sperm producin g stallions had greater serum testosterone concentration, total intrat esticular testosterone content, testicular parenchymal weight, seminif erous epithelial height, diameter of seminiferous tubules, numbers of A and B spermatogonia per testis, number of Sertoli cells per testis, and number of B spermatogonia, late primary spermatocytes, round sperm atids and elongated spermatids per Sertoli cell than low sperm produci ng stallions (P < 0.05). The number of germ cells (total number of all spermatocytes and spermatids in Stage VIII tubules) accommodated by S ertoli cells was reduced in low sperm producing stallions (18.6 +/- 1. 3 germ cells/Sertoli cell) compared with that of high sperm producing stallions (25.4 +/- 1.3 germ cells/Sertoli cell; P < 0.001). The conve rsion from (yield between) early to late primary spermatocytes and rou nd to elongated spermatids was less efficient for the low sperm produc ing stallions (P < 0.05). Increased germ cell degeneration during earl y meiosis and spermiogenesis and reduced germ cell:Sertoli cell ratio was associated with low daily sperm production. These findings can be explained either by a compromised ability of the Sertoli cells to supp ort germ cell division and/or maturation or the presence of defects in germ cells that predisposed them to degeneration. (C) 1997 by Elsevie r Science Inc.