LAUSR

Abstract The Dormer is a composite breed and constitutes the most numerous terminal sire breed in South Africa. The Elsenburg Dormer flock is the foundation flock of the breed and is still being maintained at the Elsenburg research farm in the Western Cape province of South Africa. Data from 1943 to 2019 were used to investigate genetic and environmental parameters and trends for early growth traits and lamb survival (LS) in the flock. Yearling live weight- and wool traits were recorded for a shorter period from 2008 to 2018. REML-procedures were used to estimate fixed effects as well as genetic parameters and trends in the flock. The fixed effects of birth year, sex, birth type and age of dam had a significant influence on all the early growth traits. There was an interaction between birth year and sex for most traits. Direct single-trait heritability estimates were 0.15 for birth weight (BW), 0.06 for weaning weight (WW), 0.02 for LS, 0.19 for yearling weight (YW), 0.63 for clean yield, 0.56 for clean fleece weight, 0.59 for staple length, 0.59 for staple strength, 0.60 for coefficient of variation of fibre diameter and 0.80 for fibre diameter. Maternal genetic effects amounted to 0.21 for BW, 0.08 for WW and 0.06 for YW. Dam permanent environmental effects ranged from 0.03 for LS to 0.08 for BW and litter effects from 0.12 for LS to 0.28 for BW. Multi-trait heritability estimates were fairly consistent with the above single-trait estimates. Genetic correlations among live weight traits ranged from low (-0.11) for BW and YW to very high (0.93) for WW and YW. Genetic correlations of YW with wool traits ranged from low to moderate. Genetic correlations among wool traits were mostly consistent with literature estimates for wool breeds. Genetic trends for all weight traits suggested a significant positive trend with time. Expressed relative to the overall phenotypic mean, these trends amounted to 0.12 % for BW, 0.16 % for WW and 0.45 % for YW. The study indicated that all traits were heritable and variable. Purposeful selection for a well-defined objective should allow faster genetic improvement than the annual rates of gain that were realised.