Heterogeneidade de variância e interação genótipo x ambiente para produção de leite em bovinos da raça holandesa no Estado do Paraná

Abstract

The objectives of this work was to estimate (co)variance components and genetic parameters for milk yield (MY), fat yield (FY), protein yield (PY) and for percentages of fat (%F) and protein (%P), in single-trait and three-trait analyses. 117,082 records of Holstein cows estimated for 305 days of lactations were analyzed for MY, FY and PY, while 116,747 records were used for %F and %P. All animals were officially controlled by the Serviço de Controle Leiteiro Mensal of the Associação Paranaense de Criadores de Bovinos da Raça Holandesa, from January, 1992, to December, 2003. The estimation of (co)variance components and genetic parameters for all analyzed traits was perfomed beyond Bayesian inference, using an animal model which included fixed effects of contemporary group, number of milking and linear and quadratic effects for the covariable calving age, in months. Random effects considered were both the additive genetic and the permanent environment ones. The means and standard errors for MY, FY and PY, in kg, were 8181.23 ± 5.56, 270.88 ± 0.20 and 249.01 ± 0.16, and for %F and %P were 33.33 ± 0.001 and 3.06 ± 0.0006, respectively. Heritability estimates for MY, FY, PY, %G and %P obtained in single-trait analyses were 0.26, 0.28, 0.25, 0.60 and 0.58, respectively, very close to the ones found in three-trait analyses. The estimates of genetic correlation between MY and FY, MY and PY, FY and PY, MY and %F, MY and %P and for %F and %P were 0.56, 0.89, 0.67, -0.42, -0.39 and 0.56, respectively. All estimates were obtained with high precision.