Resumo

DOMINGUEZ-VIVEROS, Joel; RODRIGUEZ-ALMEIDA, Felipe A.; ORTEGA-GUTIERREZ, Juan A.  e  FLORES-MARINELARENA, Alberto. Model selection, genetic parameters and genetic trends in national genetic evaluations of Brangus and Salers cattle. Agrociencia [online]. 2009, vol.43, n.2, pp.107-117. ISSN 2521-9766.

The objectives of the present study were to define statistical models for the national genetic evaluations of Salers (SL) and Brangus (BR) cattle, to estimate genetic parameters, and to predict genetic values (dgv=direct; mgv=maternal) and analyze their trends. The variables studied were the weights at birth (BW; SL=3583, BR = 17107) and at weaning adjusted to 205 d (WW; SL=3518, BR = 16119), using pedigrees from the Mexican Associations of SL (n=10531) and BR (n=35894) Breeders. The definition of the model started with a complete mixed model that included the fixed effect of year-season-sex-herd, plus the covariable age of the cow. As random, the model included the direct and maternal genetic effects, covariance between them and the permanent environment maternal effects. Selection of the best model was carried out with likelihood ratio tests, Akaike and Schwartz information criteria. The results of the selection of model coincide with the three methodologies used. In BR, the complete model was selected for BW and WW. In SL, the model selected for BW included the direct and maternal genetic effects, plus the covariance between them; while for WW, the model selected considered the direct and maternal genetic effects, plus the permanent environment maternal effects. The range for direct heritability based on the models selected was 0.13 to 0.20, and for the maternal heritabilities it was 0.4 to 0.8. Trends of dgv for BW and mgv for WW were negative in both breeds: -0.01 kg year^-1and -0.21 kg year^-1 in BR; -0.02 kg-1 and -0.03 kg year^-1 in SL. For WW in BR the dgv presented a positive trend (0.33 kg year-1). It is recommended to select the most adequate models before genetic evaluations. Also, a strategic analysis is required for the implications of negative genetic trends observed in mgv for WW.

Palavras-chave : Brangus; genetic evaluations; mixed models; genetic parameters; Salers; genetic trends.

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