GENETIC PARAMETERS FOR MATERNAL TRAITS IN BEEF CATTLE

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Abstract
Direct (D) and maternal (M) parameters for birth weight (BW), preweaning gain (WG) and calving ease (CE) were estimated for Angus (AN), Hereford (HE), Charolais (CH), Simmental (SM) and Shorthorn (SS). Data for the study were collected by Agriculture Canada from 1973 to 1983 for use in the National Sire Monitoring Program. Variances were estimated for each breed by a modified Method IV applied to a sire-maternal grandsire model with herd-year-seasons and age of dam × sex of calf as fixed effects. Genetic correlations (D/M) between D and M effects for WG in AN, HE, SS, CH and SM were −0.54, −0.42, −0.14, −0.26 and −0.45, respectively. Corresponding estimates of direct heritability for WG were 0.39, 0.30, 0.39, 0.27 and 0.43 and of maternal heritability 0.21, 0.27, 0.26, 0.16 and 0.20. Estimates for BW were similar to those for WG. Estimates of the D/M correlation for CE were −0.43, −0.15, −0.32, −0.74 and −0.27, of the direct heritability 0.28, 0.17, 0.19, 0.33 and 0.21, and of the maternal heritability 0.22, 0.13, 0.19, 0.23 and 0.27 for AN, HE, SS, CH and SM, respectively. Genetic trend and the introduction of new genetic lines are expected to have influenced parameter estimates. Due to negative D/M correlation estimates and moderate maternal heritabilities, selection for both the D and M components of maternal traits is advised. Key words: Variance, direct, maternal, heritability, genetic correlation, beef cattle