Peri-puberty in male Criollo horses - Testicular development, histology of the seminiferous epithelium and epididymal sperm

Abstract

The objectives of this study were to characterize age-associated changes in testicular size and blood concentrations of testosterone, as well as to evaluate the presence of epididymal sperm. Testicular maturity was evaluated by measuring seminiferous tubule diameter and the presence of the most advanced germ cells in seminiferous epithelium of horses in the peri-puberty period. The animals were surgically castrated and the thorax circumference was taken to estimate body weight. Thirty four male Criollo horses were grouped into four categories: Group I (GI) with four foals aged up to 14 months; Group II (GII) with seven animals over 14 months and less than 1 7 months; The third group (GIII) included 14 animals over 17 months and less than 19 months; Group (GIV) was composed of nine horses over 19 months and under 34 months of age. After castration, testes were weighed and measured. A segment was collected for subsequent histological evaluation, including measurement of the diameter of seminiferous tubules and the presence of germ cells of the seminiferous epithelium at different stages of development. A blood sample was collected to determine plasma testosterone. The average body weight of the animals increased significantly from 232 kg in Gl to 321 kg for horses in GIV. There was no difference between measures from the right and left testes. The testicular weight and volume was greater in animals of GIV and differed significantly compared to younger animals. Plasma levels of testosterone did not differ among age groups. The diameter of seminiferous tubules increased from 89.13 iim in foals of Gl to 168.24 tim in horses of GIV On average, 17.5% of seminiferous tubules had no germ cells in animals from Gl, decreasing to 5.4% in Gil, 5.2% in Gill and 0.8% in GIV. The number of tubules containing mature spermatids and spermatozoa increased with age. Most significant variations in the increase of testicular volume and diameter of seminiferous tubules were associated with a high presence of spermatozoa in the tubules. In conclusion all animals with 20 months of age or more had reached puberty in the present study and the first spermatozoa appeared in 16 months old colts. Animals presented epididymal sperm when testicular volume and weight were over 16 cm3 and 23 g, respectively.