Influência dos fatores ambientais sobre o crescimento de bovinos da raça nelore e estimativa de parâmetros genéticos pelos métodos Henderson 3 e REML

Abstract

Growth records collected on 2977 Nellore calves, from Ceará and Piauí state, were used to study the influence of environmental effects and to estimate the heritability and the genetic, phenotypic and environmental correlations of weaning, yearling, post-yearling weight and postweaning daily gain. Variance and covariance components were estimated by Henderson's 3 method and REML method. Two models were assumed in the analysis of variance: model 1 included fixed effects of sex, year, season and herd, a linear regression on dam's age and the random effect of sire nested within herd, model 2 joined all fixed effects in contemporary groups. Fixed effects of sex, year and herd were significant for alI the traits, (P<0,001); season of birth was significant for yearling and post-yearling weight and for post weaning, post yearling daily gain. Least square means were: 129,06 ± 1,46 kg, 186,16 ± 2,74 kg, 244,06 ± 5,23 kg, 0,341 ± 0,01 kg/d and 0,300 ± 0,02 kg/d, respectively, for weaning, yearling and post-yearling weight and for post weaning and post yearling daily gain. Dam's age at calving was significant just for yearling weight. Contemporary groups were significant for all the traits. Heritabilities by Henderson' method 3 were: 0,45 ± 0,07, 0,41 ± 0,07, 0,54 ± 0,11, 0,40 ± 0,07 and 0,27 ± 0,09, respectively, for weaning, yearling and post-yearling weight and for post weaning and post yearling daily gain. Heretabilities by REML, assuming model 1, were : 0,48 ± 0,08, 0,56 ± 0,09, 0,64 ± 0,12, 0,40 ± 0,07 and 0,28 ± 0,09, respectively, for weaning, yearling and post-yearling weight and for post weaning and post yearling daily gain. Assuming model 2 were: 0,36 ± 0,06, 0,32 ± 0,07, 0,44 ± 0,10, 0,24 ± 0,06 and 0,16 ± 0,07, respectively, for weaning, yearling and post-yearling weight and for post weaning and post yearling daily gain. Genetic correlations among weaning weight and yearling and post-yearling weight were: 0,65 ± 0,08, 0,37 ± 0,16, 0,73, 0,58, 0,81 and 0,80, respectively by Henderson' method 3 and REML. Genetic correlations between yearling and post-yearling weight were: 0,83 ± 0,07, 0,87 and 0,90, respectively by Henderson' method 3 and REML. Genetic correlations between post- weaning daily gains were: 0,35 ± 0,25, 0,24 and 0,09 respectively by Henderson' method 3 and REML. Genetic correlations between weights and daily gains were: -0, 013 ± 0,15, -0,18 ± 0,23, 0,74 ± 0,11, 0,14 ± 0,23, 0,78 ± 0,11 and 0,65 ± 0,13 by Henderson' method 3, 0,14, 0,12, 0,81, 0,12, 0,82 and 0,67 by REML assuming model 1, 0,42, 0,24, 0,75, 0,29, 0,58 and 0,75 by REML assuming model 2. Phenotipical correlations among weights, daily gains and weights and daily gains were: 0,63, 0,40, 0,65, -0,10, -0,009, -0,008, 0,76, -0,09, 0,48, 0,69 by Henderson' method 3, 0,64, 0,44, 0,63, -0,13, -0,01, -0,01, 0,77, -0,13, 0,42, 0,70 by REML assuming model 1 and 0,65, 0,52, 0,65, -0,23, 0,02, 0,06, 0,76, 0,0, 0,39, 0,65 by REML assuming model 2. Environmental correlations among weights, daily gains and weights and daily gains were: 0,62, 0,43, 0,44, -0,37, -0,006, -0,10 , 0,78, -0,27, 0,21, 0,75 by Henderson' method 3, 0, 56, 0,30, 0,32, -0,26, -0,1, -0,06, 0,76, -0,24, 0,06, 0,82 by REML assuming model 1 and 0,59, 0,40, 0,55, -0,26, -0,04, -0,01, 0,70, -0,04, 0,31, 0,65, by REML assuming model 2.