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Revista Brasileira de Zootecnia

On-line version ISSN 1806-9290


MERCADANTE, Maria Eugênia Zerlotti; PACKER, Irineu Umberto; RAZOOK, Alexander George  and  CYRILLO, Joslaine Noely dos Santos Gonçalves. Least squares and mixed model to access the estimate of direct response to selection in Nelore experimental herds. R. Bras. Zootec. [online]. 2003, vol.32, n.5, pp.1123-1130. ISSN 1806-9290.

Records of body weight at selection of Nelore cattle pertaining to the Sertãozinho's Experimental Station (SP-Brasil) Nelore herds were used to study the influence of the incorporation of additional information on the estimation of annual genetic trend by least squares and mixed model methodologies. The genetic changes in all three Nelore herds (control-NeC and selected-NeS and NeT) or only in the selected ones (NeS and NeT) were estimated, only for the females, by least squares, by mixed model including their performances and the relationship matrix, and by mixed model incorporating all available information (males and females records and the relationship matrix). The incorporation of all information provided a smoother curve of the annual means throughout the years and consequently an annual genetic trend estimate with lower standard error. Least squares provided highly variable annual estimates showing a lower capability of partitioning the genetic change from the environmental change. The mixed model analysis utilizing part of the performance records provided very low annual genetic trend estimates showing a confounding of the environmental with the genetic change.

Keywords : annual genetic trend; genetic change; selection experiment.

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