title: Increased daily sperm production in the breeding season of stallions is explained by an elevated population of spermatogonia.
abstract: Seasonal variation in number of spermatogonia and germ cell degeneration was evaluated to determine which mechanism might explain seasonal differences in daily sperm production per testis (DSP/testis) or per g parenchyma (DSP/g) in stallions. Comparing 28 adult stallions (4 to 20 yr old) in each of the nonbreeding (December-January) and breeding (June-July) seasons, the population of type A spermatogonia was more than two times greater (P less than 0.01) in the breeding season. While the number of type B spermatogonia also was elevated (P less than 0.01) in the breeding season, the number of type B spermatogonia/type A spermatogonium was similar (P greater than 0.05) between seasons. Daily sperm production/testis based on each cell type from type B spermatogonia to spermatids with elongated nuclei was lower (P less than 0.01) in the nonbreeding season. Based on DSP/g, there was significant degeneration during the meiotic divisions in the nonbreeding season. However, this reduction in potential spermatozoan production was not significant (P greater than 0.05) when considering DSP/testis. Significant germ cell degeneration also occurred in the breeding season between type B spermatogonia and primary spermatocytes. However, the type A spermatogonial population was sufficiently elevated to override this degeneration and to explain elevated production of sperm in the breeding season of stallions.
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D006736:Horses / Q000502:physiology*; D008297:Male; D008540:Meiosis; D009929:Organ Size; D012098:Reproduction; D012621:Seasons; D013076:Sperm Count; D013090:Spermatocytes / Q000166:cytology; D013091:Spermatogenesis; D013093:Spermatogonia / Q000166:cytology*; D013094:Spermatozoa / Q000166:cytology* / Q000502:physiology; D013737:Testis / Q000033:anatomy & histology