Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: July 24, 2001
Publication Date: July 24, 2001
Technical Abstract: A quadratic regression model was used to assess the influence of Brahman sires on the postweaning growth of their straightbred steer and heifer progeny. Brahman calves (n = 503), produced by 22 sires and out of 240 dams, were born from 1995 through 1999. Numbers of calves per sire ranged from 7 to 51; one sire from each year was used for two breeding seasons to tie years. After weaning, calves were penned by weight and sex and fed a high concentrate diet until the median backfat thickness for the pen was 10 mm (determined by ultrasound). Calves were weighed every 28 d and, in some cases more frequently, as a pen approached the target degree of finish. Weight records (n = 5,615) were analyzed in a model with dam, pen (as block) and residual error as random effects with estimates of 455.3, 230.4, and 415.97 kg*2, respectively (P < 0.001 for all). Sire, sex, and year were included as fixed effects, as well as regression on age at wean- ing, linear(b1) and quadratic (b2) regressions on day of feeding (day or day*2), sire sex of calf interaction, sire b1, and sire b2. The sire sex of calf interaction (P < 0.001) was evidenced by the differences between steer and heifer weights for different sires, which ranged from 4.48 to 55.15 kg. Three sires had less than 20 kg difference between steer and heifer progeny. However, one of these sires had records on only 7 progeny; the sex difference for this sire (11.5 kg) is likely the result of sampling error. The b1 and b2 regression coefficient estimates were 1.32 per day and 0.001 kg per day*2 (P < 0.001). Sire b1 regression coefficient estimates ranged from 1.07 to 1.79 kg per day (P < 0.001). Sire b2 regression coefficient estimates ranged from 0.003 to 0.0001 kg per day*2 (P < 0.001).