Testicular Development, Daily Sperm Production and Epididymal Sperm Reserves in 15-mo-old Angus and Hereford Bulls: Effects of Bull Strain Plus Dietary Energy

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Abstract
Bull calves (n = 143) were obtained from two strains of Angus and two strains of Hereford cattle for which replacements were selected on the basis of superior feedlot growth performance on either high- or medium-energy diets. From weaning to slaughter at 15 mo of age, bulls were fed either the high-energy (80% grain + 20% forage) or medium-energy diet (100% forage) corresponding to their strain. Bulls in high-energy diet groups had a greater (P<.05) scrotal circumference at 12 mo, but not 15 mo of age, than bulls in medium-energy diet groups. Compared with Hereford bulls, Angus had greater (P<.01) scrotal circumference (36.1 vs 33.9 cm) and greater (P<.05) paired testes weight (570 vs 464 g) at 15 mo of age. Daily sperm production per gram testicular parenchyma (DSP/g) was affected by strain-diet (P<.01) but not by breed. Bulls in medium-energy diet groups had 12% greater DSP/g than did high-energy diet bulls (17.4 × 106 vs 15.5 × 106). Daily sperm production (DSP) was 9% and 30% greater (P<.01) for medium-energy diet bulls in 1980 (8.2 × 109 vs 7.5 × 109) and 1981 (8.0 × 109 vs 6.2 × 109), respectively, compared with high-energy diet bulls. The effect (P<.01) of breed on DSP was attributed to breed differences in paired testes weight. Bulls in the medium-energy diet groups from weaning to 15 mo of age had 76% greater (P<.01) caput-corpus epididymal sperm reserves for Herefords in 1980 (20.1 × 109 vs 11.4 × 109) and 89% greater caput-corpus epididymal sperm reserves for both breeds in 1981 (18.5 × 109 vs 9.8 × 109) and 52% greater (P<.01) cauda epididymal sperm reserves (13.8 × 109 vs 9.1 × 109) than high-energy diet bulls. Breed did not affect epididymal sperm reserves. Estimated capus-corpus epididymal transit times for medium-energy and high-energy diet bulls were 2.2 and 1.7 d. Thus, the sperm production and reserves of young Angus and Hereford bulls should be greater if bulls are selected and managed on a medium-energy rather than a high-energy diet. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science