R. Bras. Zootec.01/Dec/2004;33(6 Sup..1):1703-10.
Estimates of crossbreeding parameters for live weight in Holstein/Gir females
DOI: 10.1590/S1516-35982004000700009
Monthly weights (18.089) of 412 females on a demonstration farm in the Zona da Mata, Minas Gerais State, were used to develop a model to describe the liveweight of cows, heifers and calves. The data were analyzed using Proc Mixed of the SAS package, separately for the following categories: a) cows, b) heifers older than 12 mo., c) heifers 70-d to 12 mo-old and d) female calves up to 70 d. For each of these, the regression equations of weight on age (mo) were, respectively, Y i = 267.730 24.319 q + 81.025 z + 1.152 x 0.007 x2 + 3.908 qx + 0.958 zx 0.017 qx2; Y i = -230.446 + 205.033 q + 76.206 z + 27.304 x 0.278 x2 11.806 qx + 0.166 qx2; Y i = -58.167 + 99.107 q + 47.627 z + 16.730 x + 0.093 x2 4.928 qx and Y i = 17.286 + 20.343 q + 11.023 z + 0.680 x + 4.117 x2 + 3.663 qx, where q is the proportion of Holstein genes and z the breed heterozygocity. The average weight maintained by cows during their herd life was estimated by integration of the predicted weight (v) between the ages at first calving and at disposal. Heterosis had important effect on this weight.
Keywords: crossbreeding; dairy cattle; heterosis; live weight