Most research shows that young first calf cows do not perform as well as older cows up to 10 years of age and most data is adjusted for age differences. Numbers were small in this group due to the practice of culling cows over ten years of age. One possible explanation for the above average performance of the young cows is probably due to selection on their dam's production record. More surprising was the observation that adapted grade Hereford calves were comparable to those of the two Brahman-derivative sire breeds. This was due to the Beefmaster sired calves averaging five and three days younger in age, respectively, at weaning than the Braford and Hereford sired calves.
Least squares means for performance traits.
3 192.8 a Differences between numbers for pregnancy and survival were due both to open cows being excluded from the latter and to culling low producing and unsound cows that were pregnant. The performance of straightbred grade Hereford calves was compared to that of offspring from comparable dams mated to Beefmaster and Braford sires. Three year-olds nursing their first calves were lower in conception than younger and older cows, showed a lower survival rate than calves from older cows. Cows ten years old and older failed to wean as heavy calves as did younger cows. These data indicate that temperate zone breeds, which have become adapted to subtropical conditions through natural selection and a period of intense artificial selection, can be made to perform competitively with breeds adapted to subtropical environments.