title: Effect of age and season on the establishment of spermatogenesis in the horse.
abstract: To determine the age at which adult values for hormonal and testicular characteristics are established, testes and blood from 123 slaughtered horses, aged 1-5 years, were compared. Serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone (T) and intratesticular testosterone (ITT) were determined by radio-immunoassay. Specimens were obtained in the non-breeding (n = 46) or breeding (n = 43) season in Experiment 1 (Exp. 1) and in the breeding (n = 34) season in Experiment 2 (Exp. 2). Testicular parenchyma was fixed in glutaraldehyde and homogenized to enumerate nuclei of Sertoli cells and elongated spermatids. Paired parenchymal weight (PPar-Wt), Sertoli cell number per horse (SC/H) and daily sperm production per gram of parenchyma (DSP/g) or per horse (DSP/H) were determined. In Exp. 1, DSP/g and SC/H were higher (P less than 0.05) in the breeding season. Left (LT-Wt; adult value established at 4 years) and right (RT-Wt; 3 years) testicular weights, PPar-Wt (4 years), DSP/g (3 years), DSP/H (3 years), SC/H (3 years), number of elongated spermatids/SC (ES/SC; 5 years), LH (5 years) and T (5 years) increased (P less than 0.01) with age. FSH also increased (P less than 0.05) with age. Age was correlated (r = 0.47 to 0.72; P less than 0.01) with LT-Wt, RT-Wt, PPar-WT, DSP/g, DSP/H, SC/H, ES/SC, LH and T. DSP/H was correlated (r = 0.40 to 0.94; P less than 0.01) with PPar-Wt, SC/H, ES/SC, LH and T. In Exp. 2, left testes were processed for histology and scored for percentage of tubules with elongated spermatids (% ES) or residual bodies (% RB). LT-Wt (adult value established at 4 years), RT-Wt (4 years), PPar-Wt (4 years), T (4 years), LH (4 years), % ES (2.5 years) and % RB (2.5 years) were influenced (P less than 0.01) by age. Age was correlated (r = 0.41 to 0.84; P less than 0.01) with PPar-Wt, % ES, % RB, LH, T and ITT. Although adult values of % ES, % RB, DSP/g and DSP/H were obtained by Year 3, PPar-Wt and serum hormonal concentrations increased significantly and DSP/H tended to increase to Year 4.
authors.affiliation: Department of Veterinary Anatomy, College of Veterinary Medicine, Texas A&M University, College Station 77843.
authors.forename: L
authors.initials: L
authors.lastname: Johnson
authors.forename: D D
authors.initials: DD
authors.lastname: Varner
authors.forename: D L
authors.initials: DL
authors.lastname: Thompson
mesh_terms: D000367:Age Factors; D000818:Animals; D005640:Follicle Stimulating Hormone / Q000097:blood; D006736:Horses / Q000097:blood / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D012621:Seasons; D012741:Sexual Maturation / Q000502:physiology*; D013091:Spermatogenesis / Q000502:physiology*; D013737:Testis / Q000502:physiology; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone