Heterosis from among British Breeds of Beef Cattle: Straightbred versus Crossbred Cows. II

This is the second paper dealing with phase two of the Virginia experiment, namely, comparison of straightbred and crossbred cows when all the calves were crossbred. The first paper covered birth and weaning information, including fertility and livability. The present paper covers post-weaning information on 214 heifers and 234 steers. The post-weaning data were found to show few differences that were biologically significant. Practically speaking, most of the differences between means of crossbred cow types and straight breds were small, indicating a decline in the influence of cow size and breeding after the calves were weaned. Some of the differences between backcross and three-breed cross calves (those for growth traits) were significant in favor of the three-breed crosses. The conclusion reached by the authors was that little heterosis existed in the crossbred cows for the post-weaning traits measured, and it was more important to have the calves crossbred than it was to have the cows crossbred. However, the dams represented only one step in a rotational crossbreeding system, so final judgment of the cows will have to await the results of further research.