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

English: Genetic parameter estimates were compared usmg Gibbs sampling and REML methods. Variance components and resulting heritabilities of birth weight (BW) and weaning weight (WW) in the Elsenburg Dormer sheep stud were estimated using a conventional (REML) and a Bayesian (GIBBS sampling) approach. A sire model with relationships included were fitted in both cases. Data from 10701 lambs recorded from 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 to seven years, and older). Sire and residual were the only random effects fitted. The posterior means (h2) ofBW and WW were 0.24 and 0.15 for REML and 0.23 and 0.16 for the Bayesian method respectively. The heritability estimates obtained were of the same magnitude and in accordance with estimates found in the literature where sire models were used. Genetic parameters for the pre-wearung growth traits BW and WW were also calculated from the (eo )variance components estimated using the ASREML program by fitting univariate animal models. Log likelihood ratio tests were done to determine the appropriate mixed models. Bivariate models were also fitted for BW and WW using as starting values for the (eo)variance components the values obtained from the univariate analysis. Fixed effects fitted were the same as in the previous section. The direct heritability (h2 a) for BW and WW for the bivariate model was 0.22 and 0.12 respectively. The maternal effects (m2 ) were 0.24 and 0.11 for BW and WW respectively. 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 WW were 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 weight weaned (TWW) and survival traits were obtained using the ASREML program fitting univariate animal models. Data for TWW were pre-corrected for fixed and random effects of sex, year and sire respectively. An animal model with only the direct random effect of animal and fixed effects of birth status and birth year of the ewe was fitted. Direct heritability (h2a) estimates of 0.12, 0.14 and 0.10 were obtained for TWW1, TWW2 and TWW3 respectively. Direct heritability (h2 a) 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 maternal environmental variance components as proportions of phenotypic variance for the three traits were 0.013 (0.005), 0.008 (0.009) and 0.023 (0.008) respectively, with service 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) and 0.00 (0.00). Permanent maternal environmental variance as a proportion of phenotypic variance for survival was 0.077 (0.017). It was concluded that Gibbs sampling could be of use to the animal breeder while the question of negative covariances between direct and maternal genetic effects still need further investigation. TWW could be used as selection criteria for reproductive efficiency.