Estimation of (Co) Variance Components and Genetic Parameters of Growth Traits for Boran Cattle

Availing information on genetic parameters of traits of interest for a given population is a prerequisite for effective genetic improvement programs. The objective of this research was to estimate the covariance components and genetic parameters of birth weight (BW), weaning weight (WW), and growth rate (ADG) traits of Boran cattle maintained at Did Tuyera cattle breeding ranch. The total number of animals considered in this study was 1162 (634 males and 528 females). The fixed effects included in the animal model for the analysis of growth traits were calf birth year, season of birth, and sex of calf. Pedigree was pruned using Relax 2 program. Covariance components were estimated using the Average Information-Restricted Maximum Likelihood (AI)-REML procedure as implemented in the DMUV.6 program. The data for BW (1120), WW (1144), and ADG (1144) were collected between 1999 and 2005. The estimation of the BW, WW, and ADG of Boran's calves was optimized by evaluating two models that either include or exclude the maternal genetic effects. The best model was chosen according to the log-likelihood ratio tests. The genetic parameters were estimated using bivariate models (DMU) package, fitting univariate and bivariate models with a restricted maximum likelihood algorithm. The sex of the calf significantly influenced BW and ADG (p< 0.01). Calf birth year and birth season significantly (p< 0.001) influenced BW, WW, and ADG. The direct heritability estimates for BW, WW, and ADG were 0.17, 0.38, and 0.46, respectively. A larger phenotypic correlation coefficient was found between BW and WW (0.28). The direct and maternal genetic correlations for BW, WW, and ADG were -0.47, -0.45, and -0.47, respectively. The relatively high heritability estimates observed (model 1) for WW (0.38) and ADG (0.46) indicated that reasonable genetic improvement for those traits might be possible through selection.