Estimation of breeding values and genetic trend of some growth traits in Merino sheep

Abstract

The aim of this study was to estimate the genetic trends for growth traits of Merino sheep managed under the National Sheep and Goat Improvement Project's breeding program. the analysis included data belonging to 3116 lambs born to 83 rams and 1129 ewes. The data [birth weight (BW), live weight at 45th day (LW45), weaning weight (WW-90th day) and average daily gain from birth to weaning (ADG)] were collected over a period of 6 years. BW demonstrated a positive and significant genetic correlation with all growth traits, but had a low direct heritability (0.02 +/- 0.02). Birth weight had high genetic correlation with all growth traits. Except for the high correlation between LW45 and WW (0.51), the remaining traits had medium or low phenotypic correlations. While the genetic trend values for LW45 in lambs, ADG, WW and growth index (GI) in rams and ADG, LW45 and GI in ewes were all positive, they were not statistically significant. However, the genetic progression for GI, WW and ADG in lambs were found to be negative and significant (p < 0.05). Genetic trend estimates indicated that there wasn't a positive genetic improvement in the growth traits studied in Merino sheep. Thus, it is proposed to improve genetic trends by the implementation of selection as based on BLUP.