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

[摘要] 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 theElsenburg Mutton Merino sheep Stud and used in this study for estimation of geneticparameters and genetic and environmental trends. BWT and WWT were collected duringthe period 1955 to 1999 while YRWT and wool trait data were collected in the years1983 to 1999.Eight animal models formed from ignoring or inclusion of maternal genetic andenvironmental effects and direct-maternal covariance were used to identify the bestmodel for estimation of genetic parameters from both univariate and bivariate analysis.Yearly means of phenotypic performance and breeding values were used to evaluateenvironmental and genetic trends.Preliminary fixed model analysis showed that the fixed effects identified as having asignificant (P< 0.001) effect on growth traits (BWT & WWT) were sex, birth status, ageof dam and year. Year had a significant (P< 0.0001) effect on yearling weight and allfleece traits. Sex had a significant (P< 0.0001) effect on yearling weight, fleece weightsand clean yield. Birth status had a significant (P< 0.0001) on yearling weight and fleeceweights, and significant (P< 0.001) effect on mean fibre diameter. Age of dam hadsignificant (P< 0.001) effect only on yearling weight. Some significant interactions werealso 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 ± 0.16for 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 wereimportant for BWT, WWT, YRWT, and GFW while maternal genetic effects also had asignificant 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 forBWT, WWT, YRWT, GFW, CFW and MFD respectively. Maternal heritability estimatesof 0.20, 0.05, 0.05, 0.02 and 0.06 were obtained for BWT, WWT, YRWT, GFW andCFW, respectively.The correlation between direct and maternal effects for growth traits were consistentlynegative, but positive for all fleece traits except for MFD.Phenotypic correlations were generally positive and low to medium. Genetic correlationswere also generally positive and low to medium. The genetic correlation between CFWand 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 breedingvalues was negative for all traits. Genetic trends were small but positive. The highmaternal trend for WWT reveal that the biggest genetic improvement was in the maternalgenetic ability of ewes to produce heavier lambs

[发布机构] University of the Free State