The objective was to estimate genetic correlations between body weight (BW), scrotal circumference and visual evaluation scores of body conformation measured at standard ages in Guzerat cattle. All measurements were performed at 205 (weaning age), 365, 450 and 550 days of age; for BW, two additional measurements (at birth and 120 days of age) were realized. The data utilized in this study were retrieved from a database of the Brazilian Association of Zebu Breeders that contained information of registered Guzerat animals born between 1970 and 2013. Genetic parameters were estimated in bi-trait analyses by using Bayesian inference. Genetic correlations between BW at 205 and 450 days of age with other traits were high and positive, whereas the correlations between visual evaluation scores with other traits were moderate. Based on correlations herein obtained, we conclude that selection based on BW results in increased visual scores and scrotal circumference, leading to improvements in productive performance and animals with best body conformation.

O objetivo deste trabalho foi estimar herdabilidades, correlações genéticas e fenotípicas e tendências genéticas das características morfológicas e de tipo de caprinos da raça Saanen nascidos no Brasil de 1979 a 2009. Dados de 1243 caprinos, 197 machos e 1046 fêmeas, foram utilizados para estimar parâmetros genéticos e tendência das características: perímetro torácico, comprimento corporal, altura na cernelha, altura, largura e comprimento da garupa, bem como as principais características que definem o padrão racial e a aptidão do animal (paleta e linha superior, membros e pés, tipo leiteiro, capacidade de corpo, úbere, ligamento traseiro e dianteiro, textura do úbere, tetos e nota). Os componentes de variância foram estimados pelo método da máxima verossimilhança restrita em análise multicaracterística. A tendência genética foi obtida por meio da regressão dos valores genéticos médios por ano de nascimento. As estimativas de herdabilidade das características morfofuncionais variaram de 0,08 a 0,45, as correlações genéticas de -0,58 a 0,89 e fenotípicas de -0,11 a 0,87. A tendência foi de um leve declínio ao longo dos anos para a maior parte das características avaliadas, o que evidencia a existência de variabilidade genética aditiva entre os animais, mas demonstra que a seleção praticada tem sido pouco efetiva.

Our objective was to estimate genetic parameters, and genetic and phenotypic trends for bodyweight (BW; measured at birth, 120, 205 (weaning age), 365, 450 and 550 days of age), scrotal circumference, and visual appraisal scores of body conformation in Guzerat cattle. Data regarding body structure, finishing precocity, muscling, sheath and navel, breed characteristics, limbs (soundness of feet and legs), and sexuality, which were visually appraised, were obtained from the Brazilian Association of Zebu Breeders, recorded between 1970 and 2013 in five Brazilian states. Variance components and heritability were estimated by using linear animal (for continuous variables) and threshold (for categorical variables) models using Bayesian inference. Genetic and phenotypic trends were obtained by regressing the average annual genetic value relative to animal’s birth year. The direct heritability values for BW were high, ranging from 0.38 to 0.45, whereas the maternal effect was responsible for 17–23% of the phenotypic variation. For scrotal circumference, the direct heritability values were median with values ranging from 0.08 and 0.15, whereas for visual appraisal scores, the values were median to high (0.07–0.18). Higher response to selection for BW traits is expected for those with moderate to high heritabilities. The estimated genetic trends indicated favourable changes for BW with average annual changes of 396, 2948, 3388, 5808, 8184, and 8096 g for BW at the respective ages. The genetic values were decreasing over the years for scrotal circumference, body structure, finishing precocity, muscling, and sheath and navel. Therefore, a longer evaluation period should be utilised to assess these traits as little time has elapsed from the beginning of the selection until the time of the present study.

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