Genetic improvement of production and wool traits in the Elsenburg Mutton Merino flock

English: A total of 10717, 7795, and 2021 records of birth weight (BWT), weaning weight (WWT), and yearling weight (YRWT), respectively, and 1965 records of greasy (GFW) and clean fleece weight (CFW) and mean fibre diameter (MFD) were collected from the Elsenburg Mutton Merino sheep Stud and used in this study for estimation of genetic parameters and genetic and environmental trends. BWT and WWT were collected during the period 1955 to 1999 while YRWT and wool trait data were collected in the years 1983 to 1999. Eight animal models formed from ignoring or inclusion of maternal genetic and environmental effects and direct-maternal covariance were used to identify the best model for estimation of genetic parameters from both univariate and bivariate analysis. Yearly means of phenotypic performance and breeding values were used to evaluate environmental and genetic trends. Preliminary fixed model analysis showed that the fixed effects identified as having a significant (P< 0.001) effect on growth traits (BWT & WWT) were sex, birth status, age of dam and year. Year had a significant (P< 0.0001) effect on yearling weight and all fleece traits. Sex had a significant (P< 0.0001) effect on yearling weight, fleece weights and clean yield. Birth status had a significant (P< 0.0001) on yearling weight and fleece weights, and significant (P< 0.001) effect on mean fibre diameter. Age of dam had significant (P< 0.001) effect only on yearling weight. Some significant interactions were also found, but since they were very small, they were ignored. Least-squares means were 4.24 ± 0.11 for BWT, 18.7 ± 1.73 For WWT, and 51.4 ± 0.16 for YRWT; 3.37 ± 0.18 for GFW, 2.19 ± 0.12 for CFW and 23.1 ± 0.04 (µrn) for MFD. Maternal genetic, permanent environmental, and common environmental effects were important for BWT, WWT, YRWT, and GFW while maternal genetic effects also had a significant contribution to CFW. The basic direct model was adequate for MFD. Direct heritability estimates of 0.08, 0.04, 0.18, 0.37, 0.34 and 0.67 were obtained for BWT, WWT, YRWT, GFW, CFW and MFD respectively. Maternal heritability estimates of 0.20, 0.05, 0.05, 0.02 and 0.06 were obtained for BWT, WWT, YRWT, GFW and CFW, respectively. The correlation between direct and maternal effects for growth traits were consistently negative, but positive for all fleece traits except for MFD. Phenotypic correlations were generally positive and low to medium. Genetic correlations were also generally positive and low to medium. The genetic correlation between CFW and GFW was close to unity with a small standard error. Breeding values were obtained as a by-product of the ASREML procedures. Environmental change, calculated as the difference between phenotypic and breeding values was negative for all traits. Genetic trends were small but positive. The high maternal trend for WWT reveal that the biggest genetic improvement was in the maternal genetic ability of ewes to produce heavier lambs