Date of this Version
Thirty-six Landrace x Large White cross boars were selected from litters with either high or low estimated breeding values for 150-d paired testis weight. Blood samples were taken via jugular venipuncture at eight ages (42, 56, 70, 84, 98, 112, 126 and 140 d). At each sampling age, nine blood samples were taken at 30-min intervals. Luteinizing hormone (LH) was determined on the individual serum samples. Serum samples from each boar at each age were pooled and concentrations of follicle-stimulating hormone (FSH), estradiol-17β (E2) and testosterone (T) were determined. Paired testis width, testis length and body weight were measured at 98, 112, 126 and 140 d of age. Backfat probe, weights of excised testes and histological data on testes were obtained at 140 d of age. Boars with high testis weight (HTW) were heavier (P<.05), had higher adjusted backfat probes (P<.01) and had consistently larger in situ testis measurements (P<.01) than did low testis weight (LTW) boars. Boars with HTW had heavier (P<.01) testes and epididymides at 140 d of age. They also had a higher percentage of seminiferous tubules in which spermatogenesis was present (P<.05), a larger percentage of tubules with a lumen (P<.05) and tubules had a larger mean diameter (P<.01) than did those of boars with LTW. Adjustment of in situ testis measurements and excised testis weights for body weight reduced line differences by less than 20%. A rise in LH concentrations occurred at approximately 100 d of age. Boars with HTW had higher (P<.05) and more variable (P<.01) LH concentrations than did boars with LTW. Boars with HTW also had higher maximum concentrations of LH during the pubertal rise (P<.01) and these concentrations tended to reach maximum levels at younger ages. Concentrations of T increased in a fashion that was nearly linear with age (P<.01) and tended to be higher for the boars with HTW (P<.10). Concentrations of E2 changed little from 42 to 84 d of age but increased steadily thereafter. Boars with HTW had a more rapid increase in E2 concentrations than did boars with LTW (P<.05). Concentrations of T and E2 were similar for boars of the HTW and LTW groups after adjustment to a constant testis size. The results suggest that testis size will respond to selection in swine and that genetic changes in testis size are associated with changes in LH concentrations.