Genetic parameters for live weight traits in South African terminal sire sheep breeds

Genetic parameter estimates for live weight traits were derived using Residual Maximum Likelihood (REML) procedures for the South African Dormer, Ile de France and Merino Landsheep terminal sire sheep breeds. Birth weight and weaning weight records were available for all breeds. However, pre-weaning weights were available for only the Ile de France and Merino Landsheep breeds, while post-weaning weights were available only for the Dormer breed. Direct heritability estimates (h2) derived using single-trait analyses were 0.25, 0.28 and 0.37 for birth weight, weaning weight and post-weaning weight respectively for the Dormer breed. Corresponding h2 estimates for the Ile de France and Merino Landsheep breeds were respectively 0.13, 0.53 and 0.14 and 0.23, 0.36 and 0.17 for birth weight, pre-weaning weight and weaning weight. The haphazard data structure of the respective populations resulted in complications in the partitioning of maternal effects into maternal genetic (m2) and maternal permanent environmental (c2) components. Low to moderate maternal heritability (m2) and dam permanent environmental (c2) estimates were derived for the Dormer and Ile de France breeds. Genetic, phenotypic and environmental correlations were estimated using three-trait analysis and were found to be moderate to high for live weight traits in the Dormer and Ile de France breeds. The moderate genetic parameter estimates obtained in this study led to the conclusion that direct selection for live weight traits in the terminal sire breeds will result in improved growth in the terminal sire sheep breeds.