Estimation of genetic parameters and variance components of pre-weaning growth traits in Barki lambs

Abstract Growth performance has a substantial impact on the profitability of any animal production enterprise. Hence, it should be considered in breeding programs and genetic improvement strategies. The objective of this study was to estimate genetic parameters and (co)variance components of pre-weaning growth traits in the Egyptian Barki sheep breed. A total of 5203 lambs with full pedigrees descended from 133 rams and 1876 ewes were included in this study from 1972 to 2015. The traits included in this study were birth weight (BW), weaning weight (WW) and pre-weaning average daily gain (ADG). Restricted maximum likelihood (REML) using different animal models ignoring or including maternal effects were evaluated. Based on the most appropriate model, direct heritabilities for BW, WW and ADG were estimated to be 0.07, 0.15 and 0.16, respectively. Maternal effects accounted for approximately 15%, 6% and 10% for the same traits, respectively. Apparently, maternal effects had a notable influence on variance estimates in case of BW, but these effects have declined as the lamb age increased. This effect was also accompanied by increasing direct heritabilities in case of WW and ADG. The direct-maternal genetic covariance was always negative and its average values were −0.22 ± 0.08, −0.35 ± 0.2 and −0.45 ± 0.18 for BW, WW and ADG, respectively. The pairwise correlations between the studied traits were 0.3 ± 0.01 and 0.4 ± 0.01 (BW and WW), 0.5 ± 0.01 and 0.12 ± 0.01 (BW and ADG) and 0.92 ± 0.01 and 0.91 ± 0.01 (WW and ADG) for phenotypic and genetic correlations, respectively. The moderate heritability estimates for WW and ADG showed that these traits could respond to selection whereas the genetic improvement in BW would be little due to its lower heritability. The genetic and phenotypic trends in the investigated traits suggested that the genetic progress during the study period was very small. Such information is important in designing appropriate management and breeding strategies for early-life growth traits in Barki sheep.