Genetic and environmental variances in lamb production traits of Merino ewes in a Mediterranean Environment

Abstract

Parameter estimates for number of lambs born (NLB), number of lambs weaned (NLW) and total weight of lamb weaned (TWW) per lambing opportunity were derived for a Western Australian resource flock. Reproduction was found to increase with ewe age, up to an age of 4 years. No further improvement was observed subsequently. Heritability estimates were 0.053 for TWW, 0.060 for NLB and 0.042 for NLW, when expressed as a ratio of the overall phenotypic mean. Corresponding ewe permanent environmental estimates were 0.132, 0.109 and 0.130. The random effect of service sire contributed between 3% and 4% to the overall phenotypic variance for reproduction traits. Bloodline differences were very small. Genetic and ewe permanent environmental correlations between reproduction traits were high, exceeding 0.8 in all instances. Phenotypic and environmental correlations were somewhat lower.