title: Genetic analysis of body weights of individually fed  beef bulls in South Africa using random regression models.
abstract: The aim of this study was to estimate genetic  parameters for body weights of individually fed beef bulls measured at  centralized testing stations in South Africa using random regression models.  Weekly body weights of Bonsmara bulls (N = 2919) tested between 1999 and 2003  were available for the analyses. The model included a fixed regression of the  body weights on fourth-order orthogonal Legendre polynomials of the actual days  on test (7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, and 84) for starting age  and contemporary group effects. Random regressions on fourth-order orthogonal  Legendre polynomials of the actual days on test were included for additive  genetic effects and additional uncorrelated random effects of the  weaning-herd-year and the permanent environment of the animal. Residual effects  were assumed to be independently distributed with heterogeneous variance for  each test day. Variance ratios for additive genetic, permanent environment and  weaning-herd-year for weekly body weights at different test days ranged from  0.26 to 0.29, 0.37 to 0.44 and 0.26 to 0.34, respectively. The  weaning-herd-year was found to have a significant effect on the variation of  body weights of bulls despite a 28-day adjustment period. Genetic correlations  amongst body weights at different test days were high, ranging from 0.89 to  1.00. Heritability estimates were comparable to literature using multivariate  models. Therefore, random regression model could be applied in the genetic  evaluation of body weight of individually fed beef bulls in South Africa.
authors.affiliation: Animal Production Institute, Agricultural Research Council, Irene, South Africa. wselapa@arc.agric.za
authors.forename: N W
authors.initials: NW
authors.lastname: Selapa
authors.forename: K A
authors.initials: KA
authors.lastname: Nephawe
authors.forename: A
authors.initials: A
authors.lastname: Maiwashe
authors.forename: D
authors.initials: D
authors.lastname: Norris
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001835:Body Weight / Q000235:genetics*; D002417:Cattle / Q000235:genetics*; D058751:Livestock / Q000235:genetics; D008297:Male; D008962:Models, Theoretical; D013019:South Africa