Woolfolk, Matthew (2014-08). Estimation of Genetic Parameters for Post-Weaning Performance Traits in Brahman and Brahman-Influenced Stocker Cattle on Forage-Based Studies. Master's Thesis.
The objectives of this study were to estimate heritability of performance traits in Brahman and Brahman-influenced (Â¼ or Â½ Brahman) stocker cattle on cool-season (n = 1,732) and warm-season (n = 1,199) forages. Cattle were born from 1986 to 2011 at the Texas A&M AgriLife Research and Extension Center at Overton, TX. Traits included end of period body weight (BW), average daily gain (ADG), and body condition score (BCS). Data were analyzed for each season using animal models, with main effects including stocking rate (3 levels), breed type (3 levels), supplementation (2 levels), and contemporary groups constructed by sex and year. Age was fit as a linear covariate. Across levels of stocking rate, calves at low stocking rates had heavier BW, higher ADG, and higher BCS than calves at medium and high stocking rates. For cool-season ADG and BCS, an interaction between breed type and supplementation was included (P = 0.002). Supplemented calves had higher BCS across all breed types, while only Â¼ Brahman ADG was greater for supplemented cattle. All warm-season traits differed between levels of supplementation. For warm-season, Â¼ Brahman had the heaviest BW, while Â½ and purebred Brahman did not differ (P = 0.39). For ADG, Â½ Brahman was greater than Â¼ Brahmans and purebreds, which did not differ (P = 0.10). No difference in warm-season BCS between breed types was detected. Heritability estimates for cool-season BW, ADG, and BCS were 0.72 Â± 0.094, 0.14 Â± 0.083, and 0.25 Â± 0.099, respectively. For warm-season forages, heritability estimates for BW, ADG, and BCS were 0.44 Â± 0.130, 0.15 Â± 0.099, and 0.29 Â± 0.106, respectively. The estimates for ADG and BCS in both seasons corresponded with estimates of similar traits in other experiments, as did the estimate for warm-season BW. The estimate for cool-season BW seemed high. Potential causes included influence of breed type on heritability estimates, as documented in other studies, as well as differences between traits in seasons, where measurements of the same trait in different environments could differ.