Bolívar Vergara, Diana MaríaRamírez Toro, Edison JuliánVergara Garay, Oscar DavidRestrepo Betancur, Luis FernandoArboleda Zapata, Elkin MauricioCerón Muñoz, Mario Fernando2012-07-092012-07-0920091794-4449http://hdl.handle.net/10567/510Introduction. The weight, in the moment of birth, is linked to the strength and the survival of beef and is one of the most important factors in death rates during the cattle’s first 24 hours of life. The genetic evaluation for this characteristic must be included as a part of the election criteria in genetic improvement programs. Objective. To estimate the variance components and the genetic parameters for the weight at the moment of birth in a population of crossed beef in the low tropical Colombian zone. Materials and methods. The estimations of the variance components were obtained by the use of the Derivative-free restricted maximum likelihood method. The model included, as fixed effects, herd, individual and maternal genetic group, contemporary group (sex, time and year of birth) and the age of the cow at the birth moment as a covariate. The random effects were the genetic direct and maternal additives, permanent environment of the cow and residual. Results. Direct and maternal heritabilities were 0.24 ± 0.027 and 0.01 ± 0.009, respectively. Differences were found among genetic groups for the characteristic analyzed. The ½A ¼S ¼C, ½A ¼R ¼C, ¾C ¼B y ¾C ¼A groups had, at the moment of birth, a weight superior to that of the Zebu, while the groups ½B ¼A ¼C, ¾A ¼C, ½B ½C, ½R ¼A ¼C, ½R ½C and 9/16 A 7/16 C had a lower weight. Conclusions. The direct heritability found suggests that the selection by the use of this characteristic is feasible for this population. The differences found among genetic groups must be kept in mind, in order to achieve intermediate weights in the moment of the birth.esGanado de carneCorporación Universitaria LasallistaGenéticaGenética de ganado vacunoGanado de carne - Mejoramiento de la especieCruzamientoGanado de carne - ReproducciónArticle