Avaliação genética de parte da trajetória de crescimento de ovinos das raças santa inês, poll dorset e somalis brasileira utilizando modelos de regressão aleatória

Abstract

Data set of 220, 336 and 19,303 records, respectively of Poll Dorset, Somalis Brasileira and Santa Inês sheep, born between 1996 and 2008, belonging to Gaasa Agropecuária Ltda, supported by Programa de Melhoramento Genético de Caprinos e Ovinos de Corte (GENECOC) of Embrapa Caprinos e Ovinos, were analyzed with the aim to evaluate distinct polynomial functions with different order of fit for fixed and random regressions of growth trajectory and to estimate (co)variances components and genetic parameters of this trajectory. Fixed effects used in analysis for all breeds were contemporary group (animals born in the same year-season), sex and birth type (single, twin, triple). Separately, for each breed, 24 models, with different orders, were evaluated to verify the best fit for fixed trajectory and for random regression of additive direct, maternal and permanent environmental effects. Ordinary and Legendre polynomials, varying of two (linear) to four (cubic) orders, were evaluated for fixed regression of average growth trajectory. Legendre and quadratic bspline functions, varying of three (quadratic) to four (cubic) orders, were evaluated for random regressions. For all breeds, Legendre polynomials of order fourth were sufficient to fit random regression. However, in fixed regression, ordinary polynomials were best to Poll Dorset and Santa Inês breeds, while Legendre were best for Somalis Brasileira. Fixed trajectory was linear for Poll Dorset and Somalis Brasileira and quadratic for Santa Inês. In Poll Dorset, direct heritability was low (<0.05) until 100 days, when so increased until 212 days reaching 0.74. In major portion of trajectory, maternal heritability for this breed were higher than direct heritability, this last overpass the first only after 150 days of age, about 100 days after weaning of animals. In Somalis Brasileira breed, the standard of direct heritability estimates presented two parabolas: one between birth and 73 day, with maximum of 0.21 at 49 days, and other from 73 day to rest of trajectory, with maximum of 0.53 at 253-256 days. Maternal heritability increased until 76 day, with maximum of 0,95, decreasing for 0.47 at 261 day, increasing again until final of trajectory, reaching 0.80. In Santa Inês breed, direct heritabilities at days 1, 50, 150, 250 and 411 were 0.24, 0.12, 0.44, 0.84 and 0.96, respectively, while maternal heritabilities for the same ages, respectively, were 0.24, 0.19, 0.09, 0.02 and 0.01. In all breeds, genetic correlations among weights in subsequent ages were high, tend to unity, with negative correlations between weights at early ages and weights at late ages. There is sufficient genetic variability to permit selection of these breeds for alter its growth trajectory. However, differences in standard of this variability suggest different procedures for selection of each breed. Genetic control of weights at initial ages is not the same in late ages. This aspect is important for establishment of adequate strategies of selection. Selection of animals for slaughter in early age must be different of that to replacement animals