Estimation of genetic parameters and maternal effects for body weight at different ages in D\'man sheep

Abstract The objective of this study was to estimate the genetic parameters for birth weight (BW), weight at 30 days (W30), 90 days (W90) and 135 days (W135) of D’man sheep. Records used in the study were collected over a period of 25 years (1988–2012) from 4728 lambs that descended from 129 sires and 621 dams. (Co) variance components and genetic parameters were estimated with univariate and bivariate animal models using the restricted maximum likelihood (REML) procedure. Age of dam, type of birth, sex of lamb and period of birth showed significant effects on studied weights, so they were considered as in the analysis models. Twelve different animal models were fitted by including or excluding maternal additive genetic effects, maternal permanent environmental effect, maternal temporary environmental effect and covariance between direct-maternal additive genetic effects. The most appropriate model for each trait was determined based on Akaike’s Information Criterion (AIC). Bivariate analysis was performed using the most appropriate models obtained in univariate analysis. Based on the best model, direct heritability estimates were 0.05 ± 0.02, 0.03 ± 0.02, 0.08 ± 0.03 and 0.12 ± 0.04 for BW, W30, W90 and W135, respectively. Maternal effects significantly influenced the growth traits. The maternal heritability for BW, W30 and W90 were 0.10 ± 0.02, 0.07 ± 0.03 and 0.07 ± 0.03, respectively. Direct-maternal additive genetic correlations were negative and medium ranging from −0.04 to −0.54 for BW, W90 and W135, but positive and medium to high for W30 (0.25–0.71). The maternal permanent environmental effects as a proportion of total variance were 0.10, 0.05 and 0.09 for W30, W90 and W135, respectively. The maternal temporary environmental effects were 0.18, 0.09, 0.08 and 0.07 for BW, W30, W90 and W135, respectively. The estimates of direct genetic correlation between BW–W30, BW–W90, BW–W135, W30–W90, W30–W135 and W90–W135 were 0.84 ± 0.23, 0.66 ± 0.24, 0.81 ± 0.15, 0.92±  0.09, 0.93 ± 0.05, 1.00 ± 0.01, respectively. The estimates of the phenotypic correlation among traits were positive and ranged from 0.31 for BW–W135 to 0.87 for W90–W135. In conclusion, maternal effects on weights of D’man sheep are important and need to be considered in any selection programme undertaken for this breed.