Genetic parameter estimation of production and reproduction traits of the Elsenburg Dormer stud

[摘要] English: Genetic parameter estimates were compared usmg Gibbs sampling and REMLmethods. Variance components and resulting heritabilities of birth weight (BW) andweaning weight (WW) in the Elsenburg Dormer sheep stud were estimated using aconventional (REML) and a Bayesian (GIBBS sampling) approach. A sire model withrelationships included were fitted in both cases. Data from 10701 lambs recordedfrom 1943 to 1999 were used in the analyses. Effects fitted as fixed were sex (male,female); birth status (single; twin, triplet); year (1943-1999) and age of dam (two toseven years, and older). Sire and residual were the only random effects fitted. Theposterior means (h2) ofBW and WW were 0.24 and 0.15 for REML and 0.23 and 0.16for the Bayesian method respectively. The heritability estimates obtained were of thesame magnitude and in accordance with estimates found in the literature where siremodels were used.Genetic parameters for the pre-wearung growth traits BW and WW were alsocalculated from the (eo )variance components estimated using the ASREML programby fitting univariate animal models. Log likelihood ratio tests were done to determinethe appropriate mixed models. Bivariate models were also fitted for BW and WWusing as starting values for the (eo)variance components the values obtained from theunivariate analysis. Fixed effects fitted were the same as in the previous section. Thedirect heritability (h2a) for BW and WW for the bivariate model was 0.22 and 0.12respectively. The maternal effects (m2) were 0.24 and 0.11 for BW and WWrespectively. These m2 values fall within the range 0.09 to 0.31 found in literature.The direct-maternal genetic correlations (ram) of -0.38 and -0.38 for BW and WWwere similar to those found in literature.Genetic parameter estimates for reproduction traits, i.e. number of lambs born (NLB),number of lambs born alive (NLBA), number of lambs weaned (NL W), total weightweaned (TWW) and survival traits were obtained using the ASREML program fittingunivariate animal models. Data for TWW were pre-corrected for fixed and randomeffects of sex, year and sire respectively. An animal model with only the directrandom effect of animal and fixed effects of birth status and birth year of the ewe wasfitted. Direct heritability (h2a) estimates of 0.12, 0.14 and 0.10 were obtained forTWW1, TWW2 and TWW3 respectively.Direct heritability (h2a) and (SE) estimates of0.103 (0.016),0.101 (0.016) and 0.031(0.011) were obtained for NLB, NLBA and NLW respectively. Permanent maternalenvironmental variance components as proportions of phenotypic variance for thethree traits were 0.013 (0.005), 0.008 (0.009) and 0.023 (0.008) respectively, withservice sire variance as a proportion of phenotypic variance of 0.005 (0.004),0.007(0.004) and 0.006 (0.003) respectively for the traits mentioned.Heritability estimates for direct and maternal effect of survival were 0.03 (0.018) and0.00 (0.00). Permanent maternal environmental variance as a proportion ofphenotypic variance for survival was 0.077 (0.017).It was concluded that Gibbs sampling could be of use to the animal breeder while thequestion of negative covariances between direct and maternal genetic effects still needfurther investigation. TWW could be used as selection criteria for reproductiveefficiency.

[发布机构] University of the Free State