Epididymal sperm reserves in 12-month-old Angus and Hereford bulls: Effects of bull strain plus dietary energy

Abstract

Bull calves ( n = 103) were obtained from two strains of Angus and two strains of Hereford cattle developed by selecting replacements on the basis of superior feedlot growth performance within breed on either high- or medium-energy diets. From weaning to slaughter at 12 months of age at the end of a 168-day growth performance test, bulls of one strain of each breed were fed the high-energy diet (80% grain +20% forage; 13.064 MJ/kg) and bulls of the second strain were fed the medium-energy diet (100% forage; 9.110 MJ/kg). At one year of age, Angus bulls had heavier ( P < 0.01) testes than Hereford bulls (409 vs. 330 g). Level of dietary energy did not affect paired testicular or paired epididymal weight. Compared with Hereford bulls, Angus had greater ( P = 0.06) cauda epididymal sperm reserves (4.9 × 10 9 vs. 3.6 × 10 9 spermatozoa). Bulls fed the medium-energy diet during the 168-day growth performance test and slaughtered at 12 months of age had 41% greater ( P < 0.05) caput-corpus epididymal sperm reserves (4.8 × 10 9 vs. 3.4 × 10 9 spermatozoa), 58% greater ( P < 0.01) cauda epididymal sperm reserves (5.2 × 10 9 vs. 3.3 × 10 9 spermatozoa), and 52% greater ( P = 0.01) total epididymal sperm reserves (9.9 × 10 9 vs. 6.5 × 10 9 spermatozoa) than bulls in the high-energy diet group. Thus, the sperm reserves of yearling Angus and Hereford bulls appear to be greater if bulls are selected and managed on a medium-energy rather than a high-energy diet.