CLIMATE SPATIALIZATION AND GENOTYPE-ENVIRONMENT INTERACTION EFFECTS ON WEANING WEIGHTS OF NELLORE CATTLE IN EXTENSIVE SYSTEMS IN TROPICAL REGIONS OF BRAZIL

ABSTRACT

Abstract Depending on the environmental differences among the regions, the phenotypic expression in beef cattle may significantly vary between the progenies of the same sire, and this is an important rule to identify the best animal. Thus, this study was carried out to spatialize environmental factors that may help to compare and discriminate the states of Maranhão, Pará, and Tocantins and also to check for genotype x environment interaction (G x E interaction) in these regions. The environmental variables analyzed were maximum temperature; minimum temperature; mean temperature; precipitation; normalized difference vegetation index; relative humidity; altitude; and index of temperature and humidity. Records of weaning weight of Nellore cattle raised on pasture were collected between the years of 1997 and 2007. The dataset was constituted of 21.117 animals, progenies of 161 sires. (Co)variance components and breeding values were estimated using the multiple-trait derivative-free restricted maximum likelihood method. Multivariate spatialization revealed clear distinction among the States of Maranhão, Pará, and Tocantins and allowed the identification of important environmental variables for discrimination. The estimate for direct heritability showed moderate magnitudes and were 0.22±0013, 0.26±0.021, and 0.29±0023, for the States of Maranhão, Pará, and Tocantins, respectively. The estimates of correlation between the breeding values, predicted in different States, as well as the genetic correlation for weaning weight showed that sire ranks changed among the States, indicating G x E interaction. There was a variation of the genetic response of the progeny, depending on the sire and on the State. Thus, the G x E interaction should be accounted for in the genetic evaluation of sires and the performance of Nellore cattle under extensive breeding systems in tropical regions of Brazil.

RESUMO

Resumo A expressão fenotípica pode variar significativamente sob diferenças climáticas e deve ser um motivo de preocupação na identificação e seleção de animais superiores no Brasil. Dessa forma, no presente estudo objetivou-se espacializar fatores ambientais para discriminar os estados do Maranhão (MA), Pará (PA) e Tocantins (TO) e verificar presença de interação genótipo-ambiente (IGA) para peso ao desmame em rebanhos bovinos da raça Nelore localizados nestes Estados. As variáveis ambientais analisadas foram temperatura máxima; temperatura mínima; temperatura média; precipitação; índice vegetativo normalizado; umidade relativa; altitude e índice de temperatura e umidade. Os registros de peso a desmama de bovinos da raça Nelore criados à pasto foram coletados entre os anos de 1997 e 2007 e o conjunto de dados constituído por 21.117 animais, filhos de 161 touros comuns aos Estados do MA, PA e TO. As estimativas para herdabilidades direta apresentaram magnitudes moderadas, com valores de 0,22 ± 0,013 (MA), 0,26 ± 0,021(PA) e 0,29 ± 0,023 (TO). As variáveis ambientais discriminaram bem os Estados e as estimativas revelaram variação da resposta genética da progênie, dependendo do pai e do Estado em questão. As estimativas de correlações genéticas para peso ao desmame indicaram forte presença de interação genótipo-ambiente.