BREED AND HETEROSlS EFFECTS ON TESTICULAR DEVELOPMENT AND ENDOCRINE FUNCTION OF PUBERAL BOARS 1'2

Summary Purebred and two-breed cross Duroc, Land- race, Spotted and Yorkshire boars were evalu- ated at 218 +- 6 d of age to determine the influ- ence of breed on testicular development and on concentrations of luteinizing hormone (LH) and testosterone in blood serum after treat- ment 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/~g 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 epi- didymides. Crossbred boars weighed 7 kg more (P<.05) than purebred boars. Testes, capita- corpora 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 epididy- midal sperm (28.9 -+ 1.7 x 109 vs 20.8 +- 2.1