Resumen

SCHINDLER, Valeria  y  FEOLA, Ignacio. Comparing the weight from birth to weaning of Braford calfs and crosses in NEA region, Argentina. Zootecnia Trop. [online]. 2012, vol.30, n.4, pp.335-342. ISSN 0798-7269.

In Argentina, cattle raising is in the process of being demographically relocated from the Pampean Area to the northeast and northwest of Argentina (NEA and NOA regions). Crossed livestock (quard or quadroon: without racial prevalence) is prevalent in the region, despite synthetic races, such a Braford and Brangus are gaining strength. The objective of this work was to compare Braford calves weights at birth and weaning weights within the NEA herd base. The weights of 211 calves, 72 Braford*Braford, 70 Braford*crosses and 69 crosses, were recorded at Santa Irene, a ranch owned by Ganagrín CORP, located in the Province of Corrientes. The calves were weighed at birth and weaning. Two intermediate weights were also performed, giving way to an experiment of repeated measures. The fixed effect of biotype, sex and age of calve (as a covariate) and age of cow (as covariate) were included in the analysis. Three different structures were fitted to the weight data: Unstructure (UN), Heterogeneous Compound Symmetry (HCS) and First-Order Autoregressive (1 AR), and UN were chosen as best among the three by the Akaike information criterion (AIC). Braford calves were always heavier (P<0.05) than the other two races with 30.69; 86.09; 132.90 y 160.78 kg respectively for the four weights performed. Braford*crosses weight 29.03; 81.12; 120.90 y 143.77 kg respectively and the crosses weight 26.30; 76.37; 117.67 y 138.21 kg respectively. The male calves weight 1.19 kg more than female calves (P<0.05) and there were no differences for age of calve and age of cow. The mixed model analysis allowed the effi cient calculation of the estimates of fixed effects and valid standard errors of the estimates. Modeling the covariance structure is especially important for repeated measures analysis because the measurements close in time tend to be more correlated than those further away in time.

Palabras clave : Braford; repeated measures; covariance structures; calves weight.

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