PUBERTAL DEVELOPMENT OF THE BOAR: AGE-RELATED CHANGES IN TESTICULAR MORPHOLOGY AND SELECTED ENDOCRINE PARAMETERS

Characterization of the pubertal development of the boar was investigated by monitoring various morphological and endocrinological parameters. Forty-eight Landrace X Duroc boars were assigned at weaning to one of eight castration ages (40, 70, 100, 130, 160, 190, 220 and 250 days). Blood samples were collected every 1/2-h between 0800 and 1200 h 2 days before (-2) and on days +1, +2, +3, +4, +8 and +16 after castration. Serum concentrations of testosterone (T), estradiol-17(beta) (E(,2)), cortisol (C) and luteinizing hormone (LH) were quantified by specific radioimmunoassays. The left testis was perfused with glutaraldehyde and processed for histological examination. Portions of the right testis were immediately prepared for a 3-h in vitro incubation procedure to assess T production as a response to varying dosages of human chorionic gonadotropin (hCG). Mean serum concentrations of T and E(,2) increased (P \u3c .01) in a near linear fashion with age of boar. Mean serum concentrations of T and E(,2) were 1.31, 2.24, 4.03, 9.99, 10.92, 15.75, 15.76 and 8.66 ng/ml and 11.38, 19.15, 15.75, 52.90, 89.27, 97.80, 107.95 and 118.11 pg/ml, respectively, for boars 40, 70, 100, 130, 160, 190, 220 and 250 days of age. Mean concentrations of LH before castration (day -2) did not differ with age (overall mean of 1.06 ng/ml) while serum LH concentrations were elevated (P \u3c .05) within one to two days following castration at 40, 70, 100, 130 and 160 days of age. Testicular volume percentage of seminiferous tubules increased from 36% to 72% between 40 and 250 days of age. Testicular volume percentage of Leydig cells decreased from 40% to 10% between 40 and 250 days of age. Leydig cells from boars 130 and 160 days of age had the greatest (P \u3c .01) capacity of T production when evaluated at 3125 mIU hCG/ml incubation media. Sensitivity, as judged by ED(,50) calculations, was markedly increased (P \u3c .05) in testicular tissue from boars 130 days of age and older. In conclusion, the data indicate that one factor responsible for pubertal development of the boar is an increased sensitivity of the testes to gonadotropic stimulation