Date of this Version
Purebred and two-breed cross Duroc, Landrace, Spotted and Yorkshire boars were evaluated at 218 ± 6 d of age to determine the influence of breed on testicular development and on concentrations of luteinizing hormone (LH) and testosterone in blood serum after treatment with gonadotropin releasing hormone (GnRH). Concentrations of LH and testosterone were determined in serum samples obtained from the vena cava of 139 boars just before and 1, 2, 3 and 4 h after an im injection of 200/ μg of GnRH. The right testes of 136 boars were removed and sperm numbers were determined in homogenates of testicular parenchymae, capita-corpora epididymides and caudae epididymides. Crossbred boars weighed 7 kg more (P<.05) than purebred boars. Testes, capitacorpora and caudae epididymides were heavier (P<.01) for crossbred boars (46.4 ± 10.8, 3.8 ± 1.4 and 4.8 ± 1.4 g, respectively) than for purebred boars. Crossbred boars had more testicular sperm (33.7 ± 2.0 x 109 vs 25.4 ± 2.3 x 109, P<.01), more capita-corpora epididymidal sperm (28.9 ± 1.7 x 109 vs 20.8 ± 2.1 x 109, P<.01) and more caudae epididymidal sperm (53.6 ± 2.9 x 109 vs 43.8 ± 3.8 x 109, P<.05) than purebred boars. Breed of boar influenced (P<.05) testicular weight, capitacorpora weight and sperm numbers and caudal weight and sperm numbers. Concentrations of LH and testosterone in serum were similar (P>.10) for crossbred and purebred boars at all but one sampling time. At 3 h after treatment with GnRH concentrations of LH were greater (P<.05) in crossbred than purebred boars and concentrations of testosterone were greater (P<.05) in crossbred than purebred boars at 4 h after GnRH. There was a significant breed x time interaction for concentrations of LH and testosterone. Breed of boar influenced (P<.05) concentrations of LH at 1, 2 and 3 h after treatment with GnRH, and concentrations of testosterone were affected by breed at 2 and 4 h after treatment. However, breed of boar did not influence either LH or testosterone in serum before treatment with GnRH (0 h) and LH in serum at 4 h and testosterone in serum at 1 and 3 h after GnRH. These results indicate that breed of boars influences testicular characteristics and concentrations of testosterone and LH in serum after GnRH. Heterosis was detected for testicular and epididymidal weights and sperm numbers, but heterosis was not observed for concentrations of LH and testosterone in serum.