Comparación de modelos alternativos en la evaluación genética de variables de crecimiento de ganado Brahman de registro en México

Five genetic evaluation models of registered Brahman cattle in Mexico were compared for birth weight (PN), weaning (PD), yearling (PA) and final weight at 550 days (PF), and their effect on genetic parameter estimation and EPD ordering were also assessed. Models differed on number of random factors; D, model with direct genetic effect (2d), DM, model like D plus maternal genetic effect (ω²_m) and genetic covariance between genetic effects equal to zero ((im = 0), DP, D like model plus maternal permanent effect (σ²_p), DMC, DM like model plus covariance between genetic effects (σ_dm# 0), and DMCP as the complete model, equal to DMC plus (σ²_p). Models included the fixed effect of contemporary grouping (herd, sex, year and season of birth), and age of dam as linear and quadratic covariable. A likelihood ratio test (PRV) was performed for model comparison, and EPD reordering was quantified by Spearman rank correlation analysis. The PRV showed DMC as the best model for all variables, except in PD. For PD the best model was DP. A negative genetic correlation r_dm = σdm²) was observed for PN, PA and PF (-0,86, -0,84 and -0,52, respectively) reducing the magnitude of total heritability estimates. For PD, DMC and DMCP did not converge. Correlation between selected models and the other compared models, suggested that there might be important and substantial changes on 10% of superior animals. Structure of data may modify the genetic parameter estimation if adjusting complex models; hence the model selection could be crucial before performing any genetic evaluation. Considerations were made concerning selective recording.