title: Effect of pre-weaning selection on estimates of genetic parameters and breeding values for post-weaning growth rate of beef bulls on test.
abstract: Data on South African Angus cattle consisting of 45 259 records on weaning weight (WWT), 4 360 records on average daily gain from on-farm test (ADG-D) and 1 118 from centralized test (ADG-C) were analyzed to evaluate the effect of pre-weaning selection on estimates of genetic parameters and subsequent estimated breeding values (EBV) for post-weaning average daily gain. (Co)variance components and genetic parameters for weaning weight (WWT), ADG-C and ADG-D were estimated by REML procedures fitting three different animal models. Model 1 was a univariate model of WWT, ADG-C or ADG-D and did not account for the effect of pre-weaning selection on post-weaning ADG. Model 2 was a two-trait model of WWT and either ADG-C or ADG-D. Model 3 was a multi-trait animal model including WWT, ADG-C and ADG-D. Estimates of heritability for ADG-C were 0.39 +/- 0.080, 0.42 +/- 0.060 and 0.44 +/- 0.010 from Model 1, 2 and 3 respectively. Corresponding estimates for ADG-D were 0.18 +/- 0.020, 0.19 +/- 0.020 and 0.21 +/- 0.020 respectively. Rank correlations based on EBVs for ADG-C for all bulls were 0.92, 0.83 and 0.94 for Model 1 vs. Model 2, Model 1 vs. Model 3, and Model 2 vs. Model 3, respectively and they indicated a possible re-ranking of bulls when including or excluding a correlated pre-weaning trait. Rank correlations for ADG-D also followed a similar trend. Inclusion of pre-weaning information in genetic analysis for post-weaning average daily gain is necessary to account for selection at weaning.
authors.affiliation: Department of Animal Production, University of Limpopo, Private Bag X 1106, Sovenga 0727, South Africa. mashiloane01@yahoo.co.uk
authors.forename: M L
authors.initials: ML
authors.lastname: Mashiloane
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
authors.forename: J W
authors.initials: JW
authors.lastname: Ngambi
mesh_terms: D000383:Agriculture / Q000191:economics; D000818:Animals; D001947:Breeding; D002417:Cattle / Q000235:genetics* / Q000254:growth & development*; D008297:Male; D013019:South Africa; D014886:Weaning