Direct and correlated responses to selection for autumn lambing in sheep

Table 3 Estimates and SD for variance components, as a proportion of phenotypic variances (\({\sigma }_{\mathrm{P}}^{2}\)), for birth weight (kg) and for body weight traits (BW; kg) and scrotal circumferences (SC; cm) at 60, 90, and 120 days of age

Trait	Heritability	Maternal heritability	Maternal permanent environment	Litter effect	\({\sigma }_{\mathrm{P}}^{2}\)
Birth weight	0.05 ± 0.03	0.19 ± 0.03	0.20 ± 0.05	0.29 ± 0.03	0.7
60-day BW	0.11 ± 0.03	0.14 ± 0.03	0.04 ± 0.02	0.10 ± 0.03	15.5
90-day BW	0.15 ± 0.04	0.13 ± 0.03	0.05 ± 0.02	0.07 ± 0.03	25.6
120-day BW	0.19 ± 0.04	0.13 ± 0.03	0.06 ± 0.02	0.06 ± 0.03	33.3
60-day SC	0.31 ± 0.08	0.14 ± 0.04		0.12 ± 0.05	3.6
90-day SC	0.41 ± 0.09	0.17 ± 0.05		0.10 ± 0.05	10.6
120-day SC	0.34 ± 0.09	0.16 ± 0.04		0.09 ± 0.04	9.1

Estimates of heritability, maternal heritability, maternal permanent environmental effects, and litter effects were expressed as ratios of additive genetic (\({\sigma }_{\mathrm{A}}^{2}\)), additive maternal (\({\sigma }_{\mathrm{M}}^{2}\)), maternal permanent environmental (\({\sigma }_{\mathrm{MPE}}^{2}\)), and litter (\({\sigma }_{\mathrm{L}}^{2}\)) variances, respectively, to \({{\sigma }_{\mathrm{P}}^{2}=\sigma }_{\mathrm{A}}^{2}+{\sigma }_{\mathrm{M}}^{2}+{\sigma }_{\mathrm{MPE}}^{2}+{\sigma }_{\mathrm{L}}^{2}+{\sigma }_{\mathrm{e}}^{2}\) where \({\sigma }_{\mathrm{e}}^{2}\) is the residual variance. Parameters for birth weight were derived from a bivariate model that included fertility. Parameters for BW and SC were derived from four-trait multivariate models that also included fertility. Attempts to partition maternal effects on SC into additive maternal and maternal permanent environment components did not yield reasonable results, and the final model for SC contained only additive maternal effects. SD are the standard deviation of the parameter estimates from the posterior distribution

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