TESTICULAR SIZE AT WEANING IN TROPICALLY-ADAPTED BEEF BULLS AS INFLUENCED BY BREED OF SIRE AND DAM

This study was conducted to evaluate testicular size at weaning for bu lls representing diverse tropically-adapted genotypes. Calves from 2 l ocations were weighed and castrated at weaning. In one herd, calves we re born to Brahman dams and Angus, Tuli, and Brahman sires. Body weigh ts and paired testes weights were heavier (P < 0.01) for Angus x Brahm an (AB) genotype than for Tuli x Brahman (TB) and purebred Brahman (BE ) genotype calves. The testes:body weight ratio was greater (P < 0.01) for AB than for TB and BE calves. In a second herd, calves were born to Angus cows and Brahman, Tuli, and Senepol sires. Means were similar between Brahman- (BA), Tuli(TA), and Senepol-sired (SA) calves for bo dy weight and testes:body weight ratio. Paired testes weight was heavi er (P < 0.05) for SA than BA calves. Across locations, paired testes w eights were heavier (P < 0.01) for TA than TB calves but their body we ights were similar. Within-herd deviations were greater (P < 0.01) for AB than BA calves for paired testes weight and testes:body weight rat io. The correlation between the proportion of Bos indicus genetic cont ribution and testes:body weight ratio was significantly negative. Trop ically-adapted calves differed in testicular size at weaning due to br eed of sire and dam effects. (C) 1997 by Elsevier Science Inc.