Genetic parameters for growth, reproduction and fitness traits in the South African Dorper sheep breed

Across flock genetic parameter estimates for growth, reproduction and fitness traits were derived using residual maximum likelihood (REML) procedures for the South African Dorper sheep breed. Data were retrieved from the National Small Stock Improvement Scheme (NSIS) data base from breeders that were constantly submitting performance data for a period spanning 30 years (1980-2009). Weaning weight and post-weaning weight were moderately heritable with estimates being 0.21 ± 0.01 and 0.27 ± 0.02 respectively. Maternal effects were significant, although of fairly low magnitude in live weight traits. It was demonstrated that reproductive and fitness traits such as total weaning weight per ewe lambing (TWW/L), number of lambs born per ewe lifetime (NLB/EL), number of lambs weaned per ewe lifetime (NLW/EL), lamb survival to weaning and litter size were lowly heritable with their estimates being 0.12 ± 0.02, 0.10 ± 0.01, 0.09 ± 0.01, 0.07 ± 0.01 and 0.07 ± 0.02 respectively. Selection of Dorper sheep with the objective of improving reproduction and fitness is feasible although relatively low heritability estimates indicate that annual genetic progress may be slow. Low heritabilities for ewe productive life (EPL) and stay ability at two, three and four years of age were estimated to be 0.05 ± 0.01, 0.05 ± 0.02, 0.09 ± 0.03 and 0.11 ± 0.04 respectively. This indicated that these traits are, to some extent, influenced by genetics. Lambing chances per ewe lifetime (LC/EL) and times lambed per ewe lifetime were demonstrated to have a moderate heritability (0.23 ± 0.01 and 0.11 ± 0.04 respectively) and would also result in a correlated selection response in both reproduction and longevity. No genetic basis was found for inter-lambing period (ILP). It was therefore deduced that ILP can be improved through sound management. Live weight traits were positively correlated with reproduction and fitness traits. TWW/L was genetically and environmentally positively correlated with survival, litter size and EPL. It was concluded that despite the low additive genetic variances for reproduction and fitness, genetic improvement is feasible. Therefore, breeders should incorporate these traits in their selection strategies to achieve maximum production.