Efeitos da Heterogeneidade de Variância Residual entre Grupos de Contemporâneos na Avaliação Genética de Bovinos de Corte

Abstract

RESUMO -O objetivo deste estudo foi investigar, por meio de dados simulados, o efeito da heterogeneidade de variância residual entre grupos de contemporâneos (GC) sobre as avaliações genéticas de bovinos de corte, e comparar o uso de uma avaliação genética ponderada (R≠Iσ e 2 ) em relação à avaliação que pressupõe homogeneidade de variância (R=Iσ e 2 ). A característica estudada foi ganho de peso pós-desmame corrigido para 345 dias, sendo esta simulada com variância fenotípica de 300 kg 2 e herdabilidade igual a 0,4. A estrutura de um conjunto real de dados foi utilizada para fornecer os GC e os pais referentes às observações de cada animal. Effects of Heterogeneity of Residual Variance among Contemporary Groups on Genetic Evaluation of Beef CattleABSTRACT -The objective of this study was to investigate, via simulated data, the effect of heterogeneity of residual variance among contemporary groups (CG) on genetic evaluation of beef cattle, and to compare a weighted genetic evaluation procedure (R≠Iσ e 2 )with one that assumes homogeneity of variances (R = Iσ e 2 ). Different data sets of postweaning weight gain, adjusted to 345 days, were simulated with and without heterogeneity of residual variance, using a phenotypic variance of 300 kg 2 and a true heritability of 0.4. A real data set was used to provide the CG and parents related to each animal observation. Results showed that, when high levels of heterogeneity of residual variance were considered, animals were selected from CG with higher variability, especially with intense selection. With respect to prediction consistency, non parent animals and cows had their predicted breeding values more affected by heterogeneity of residual variance than sires. The weighed factor used reduced, but did not eliminate, the effect of heterogeneity of residual variance. The results of weighted genetic evaluations were similar or superior to those from evaluations that assumed homogeneity of variances. Even when the variances were homogeneous, the weighed genetic evaluations yielded results that were not inferior than those from the usual evaluations, which assumed homogeneity of variances.

Impacto Da Distribuição De Número Desigual De Progênies Por Reprodutor Na Avaliação Genética De Animais, Em Ambientes Com Presença De Heterogeneidade De Variância Ambiental

“…Carvalheiro et al (13) , também por meio de simulação de dados, avaliando os efeitos da heterogeneidade de variância residual entre grupos de contemporâneos na avaliação genética de bovinos de corte, verificaram que esses efeitos estão associados à pressão de seleção e aos níveis de heterogeneidade, sendo que, se correções não forem feitas, rebanhos que praticam seleção intensa e que apresentam níveis acentuados de heterogeneidade de variância residual podem ter seus animais classificados de maneira incorreta e, consequentemente, menos resposta à seleção.…”

Caracterização da interação genótipo-ambiente e comparação entre modelos para ajuste do ganho pós-demama de bovinos Devon via normas de reação

“…Entretanto, diversos pesquisadores (Boldman & Freeman, 1990;Dong & Mao, 1990;Reverter et al, 1997;Torres, 1998) relatam a existência da heterogeneidade de variâncias entre rebanhos ou grupo de contemporâneos (Cavalheiro et al, 2002). Essa heterogeneidade, quando ignorada, pode ocasionar redução da resposta à seleção (Garrick & Van Vleck, 1987).…”

Sire X Herd and Sire X Herd-Year Interactions on Genetic Evaluation of Buffaloes

“…Thus, it is indicated that the effect of variance heterogeneitys is considered to reduce the risk, because they have equal or superior results to those obtained by the evaluation that assumes homogeneity of variance (Carvalheiro, et al 2002). Araújo, et al (2008b) concluded that there is variance heterogeneity among herds that exploit the milk production in Murrah buffaloes and also that the nature of this variance heterogeneity is a result of environmental factors.…”

“…However, when heritabilities are smaller in the environment in which the residual variances are greater reductions in the efficiency of selection of bulls may happen for falsely considering that the variances are homogeneous. Carvalheiro, et al (2002) observed in their study evaluating the variance heterogeneities that calves and cows have their breeding genetic values most affected by the variance heterogeneity of the bulls.…”

“…The authors concluded that genetic evaluations in Brazil should consider the variance heterogeneitys to increase the accuracy of evaluations and the selection efficiency for the milk and fat production in Holstein (Costa et al, 2000). Carvalheiro, et al (2002) observed that effects of heterogeneity of residual variance on genetic evaluations are associated with the selection pressure and heterogeneity levels. If corrections are not made, herds that practice intense selection and that present accentuated levels of residual variance heterogeneity can have their animals incorrectly classified and, consequently, less responsive to selection.…”