Effect of age and season on the establishment of spermatogenesis in the horse.
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.
Johnson
L
L
Department of Veterinary Anatomy, College of Veterinary Medicine, Texas A&M University, College Station 77843.
Varner
D D
DD
Thompson
D L
DL
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
D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone