Genetic and environmental effects on sexual precocity traits in Nellore cattle
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Data
2009-08-01
Autores
Meirelles, Sarah Laguna [UNESP]
Espasandin, Ana Carolina
Mattar, Maira [UNESP]
Queiroz, Sandra Aidar de [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Sociedade Brasileira de Zootecnia
Resumo
O objetivo neste trabalho foi estimar a herdabilidade das características probabilidade de prenhez precoce (PPP) e perímetro escrotal (PE) de animais da raça Nelore e a correlação genética entre essas características. Foram analisados dados de probabilidade de prenhez precoce de 11.696 fêmeas da raça Nelore nascidas entre 1983 e 2001. A probabilidade de prenhez precoce assumiu o valor 1 para fêmeas que efetivamente reproduziram no rebanho (19,84%) e zero para aquelas descartadas antes do primeiro parto (80,16%). O modelo para PPP incluiu os efeitos de grupo de contemporâneos, classe de idade da mãe e classe de idade à desmama da novilha, efeitos genéticos aditivos direto e residual. Foram analisadas 9.335 informações de perímetro escrotal, considerando os efeitos de grupo de contemporâneos, genético aditivo direto e residual. Os componentes de covariância foram estimados usando amostragem de Gibbs, em análise bicaracterística, utilizando-se modelo touro; a PPP, por modelo de limiar; e o perímetro escrotal, por modelo linear. As análises forneceram estimativas médias de herdabilidade iguais a 0,47 ± 0,05 e 0,27 ± 0,03 para PPP e PE, respectivamente, e de 0,12 ± 0,20 para a correlação genética entre essas características. Esses resultados indicam que existe variação genética aditiva para PPP e, portanto, essa característica deve responder à seleção. A correlação genética estimada entre PPP e PE indica associação baixa entre essas características, porém favorável. Assim, pode-se utilizar o perímetro escrotal juntamente com a PPP nas avaliações genéticas da precocidade sexual, um procedimento aumentaria a acurácia da predição da DEP (diferença esperada na progênie) da PPP.
The objective of this study was to estimate the heritability of probability of early pregnancy (PEP) and scrotal circumference (SC) and the genetic correlation between these traits in Nellore cattle. PEP records from 11,696 Nellore females born between 1983 and 2001 were analyzed. PEP was assumed to be one for females that effectively bred in the herd (19.84%) and zero for those discarded before first calving (80.16%). The model used to study PEP included the effects of contemporary group, age of dam at calving and heifer weaning age, direct additive genetic effects, and residual effects. For SC, 9335 records were analyzed considering the effect of contemporary group, direct additive genetic effects and residual effects. Covariance components were estimated by Gibbs sampling applied to a two-trait sire model, using a threshold model for PEP and a linear model for SC. Estimated mean heritability was 0.47 ± 0.05 for PEP and 0.27 ± 0.03 for SC, and the genetic correlation between traits was 0.12 ± 0.20. These results indicated the existence of additive genetic variation for PEP and this trait should therefore respond to selection. The estimated genetic correlation between PEP and SC indicated a low, but favorable, association. Thus, SC might be used together with PEP in genetic evaluations of sexual precocity. This procedure would increase the accuracy of predicting expected progeny differences for PEP.
The objective of this study was to estimate the heritability of probability of early pregnancy (PEP) and scrotal circumference (SC) and the genetic correlation between these traits in Nellore cattle. PEP records from 11,696 Nellore females born between 1983 and 2001 were analyzed. PEP was assumed to be one for females that effectively bred in the herd (19.84%) and zero for those discarded before first calving (80.16%). The model used to study PEP included the effects of contemporary group, age of dam at calving and heifer weaning age, direct additive genetic effects, and residual effects. For SC, 9335 records were analyzed considering the effect of contemporary group, direct additive genetic effects and residual effects. Covariance components were estimated by Gibbs sampling applied to a two-trait sire model, using a threshold model for PEP and a linear model for SC. Estimated mean heritability was 0.47 ± 0.05 for PEP and 0.27 ± 0.03 for SC, and the genetic correlation between traits was 0.12 ± 0.20. These results indicated the existence of additive genetic variation for PEP and this trait should therefore respond to selection. The estimated genetic correlation between PEP and SC indicated a low, but favorable, association. Thus, SC might be used together with PEP in genetic evaluations of sexual precocity. This procedure would increase the accuracy of predicting expected progeny differences for PEP.
Descrição
Palavras-chave
Beef cattle, early pregnancy, scrotal circumference, threshold trait, característica de limar, Gado de corte, Perímetro escrotal, Precocidade sexual
Como citar
Revista Brasileira de Zootecnia. Sociedade Brasileira de Zootecnia, v. 38, n. 8, p. 1488-1493, 2009.