Estimating parameters of growth curves of bulls

Parameters were estimated for nonlinear growth curves for bulls of five straightbred and 20 crossbred breed-types produced in two generations of a diallel. The primary intent of this study was to use the estimates obtained for mature size and maturing rate to define male growth in manner that would be appropriate for use in the Texas Agricultural Experiment Station (TAES) Beef Cattle Simulation Model. The results that were obtained from the nonlinear regressions made on the male growth data indicated that the relation between the mature sizes of males and females of the same breed-type is consistent with the assumption for that relation contained in the model (a ratio of 1.5). However, the inverse relationship between mature size and maturing rate that is assumed in the model was not consistent with the results of the present study. That contradiction presumably arose due to the different environment imposed on the males relative to their female counterparts. This condition prohibits direct application of the results of this study because live weights cannot be directly related to the principal growth curve contained in the model. However, such a relationship can be developed when information regarding the composition of bulls considered in this study becomes available.