| Abstrakt: |
The Hereford, Angus and Shorthorn breeds and all reciprocal crosses among them were included in this experiment, which was designed to evaluate heterosis effects in crosses among these breeds.The traits evaluated were 200-day weight, average daily gain from 200 to 396 days, from 200 to 550 days and from 396 to 550 days, 396-day weight, 550-day weight and 550-day conformation score. Data are presented and discussed for these traits on 183 heifers from two calf crops developed to produce their first calves as 3-year-olds and 173 heifers from two calf crops developed to produce their first calves as 2-year-olds. There were significant heterosis effects on 200-day weight, average daily gain from 200 to 396 days, average daily gain from 200 to 550 days, 396-day weight and 550-day weight for both management groups of heifers. Heterosis effects were not significant for average daily gain from 396 to 550 days. The reduced heterosis effects, when relatively high levels of gains were made on summer range, are interpreted to be due to a combination of a smaller effect for nonadditive genes (heterosis) on a high level of feeding and to diminished heterosis effects on growth rate after approximately 1 year of age.Interactions of years with breed of sire and breed of dam were relatively unimportant. The heterosis effects attributable to sires within a breed were not generally important. Thus, the heterosis observed was a characteristic of the breeds used rather than of specific sires within breeds.Estimates of heterosis effects on the traits measured tended to be greater for the Hereford-Angus and for the Hereford-Shorthorn combinations than for the Angus-Shorthorn combination. However, these differences were not significant. When compared with the single straightbred of each cross that produced the highest ranking steers on net merit, the crosses were generally superior.The Hereford breed was superior to both the Angus and Shorthorn breeds in crosses with the third breed. However, these differences were not generally significant.Breed effects existed for most of the triaits observed. The Herefords were superior for most measures of postweaning growth rate, and the Angus and Shorthorn were similar. |
