Growth and pubertal development of F₁ bulls from Hereford, Angus, Norwegian Red, Swedish Red and White, Friesian, and Wagyu sires

¹ U.S. Meat Animal Research Center, USDA, ARS, Clay Center, NE, 68933

^* To whom correspondence should be addressed. E-mail: Eduardo.Casas{at}ars.usda.gov.

	Abstract

The objective of the study was to characterize body growth, testicular development and puberty between 8 and 14 mo of age in bulls (n = 120) produced by mating sires from Hereford, Angus, Norwegian Red, Swedish Red and White, Friesian, and Wagyu, to MARC III ( Hereford, Angus, Red Poll, Pinzgauer) cows. Traits evaluated were birth weight, weaning weight (at 215 d), yearling weight, ADG from 8 to 14 mo of age, paired testis volume growth from 8 to 14 mo of age, age at puberty (determined by production of 50 x 10⁶ sperm with 10 % motility), age at freezable semen (determined by production of 500 x 10⁶ sperm with 50 % motility), and at 15 mo of age, paired testis weight and daily sperm production per testis pair. There was an effect of sire breed (P = 0.03) for age at puberty; animals with Wagyu and Swedish Red and White inheritance reached puberty at a later date (302 and 302 d of age, respectively) compared with Angus-sired bulls (268 d). Age at puberty for Hereford-, Norwegian Red-, Friesian-sired bulls was 270, 271, and 278 d, respectively. Differences in BW were observed (P = 0.03) at birth; bulls with Hereford and Friesian were heavier at birth (43 and 41 kg, respectively), compared with those with Norwegian Red, Swedish Red and White, and Wagyu inheritance (39, 38, and 38 kg, respectively). Differences in BW were also observed at 1 yr of age (P = 0.001), where the heaviest animals were those sired by Angus (450 kg), while the lightest animals were those sired by Wagyu (403 kg). Bulls with Wagyu inheritance had the lowest (P = 0.04) ADG (1.12 kg/d) compared with bulls with inheritance from Hereford (1.22 kg/d), Angus (1.28 kg/d), Norwegian Red (1.24 kg/d), Swedish Red and White (1.25 kg/d), and Friesian (1.27 kg/d). Differences in scrotal growth rate were not significant (P = 0.99). They ranged from 1.95 in Angus sired to 1.66 cm³/d in Wagyu sired bulls. There were no differences (P = 0.80) for age at freezable semen (335 ± 10 d). At slaughter (15 mo of age), there were no differences (P = 0.62) for paired testis weight (603 ± 28 g) and daily sperm production (10.6 x 10⁹ ± 0.9 x 10⁹ per testis pair). Growth of bulls with Wagyu inheritance was slower. Bulls with Wagyu or Scandinavian inheritance reach puberty at an older age than bulls with Angus inheritance.

Key Words: beef cattle, bulls, puberty, semen, testes