The most commonly recognised benefit of crossbreeding is hybrid vigour or heterosis. This is the amount (expressed as a percentage) by which the crossbred progeny are better than the average of the two parent breeds.
A word of warning: the performance of the progeny still depends largely on the performance of the parents. You cannot produce an outstanding line of calves from poor producing cows simply by crossbreeding. The amount of hybrid vigour will also depend on the breeds involved and the traits being measured.
Figure 1 shows the extra milk production due to hybrid vigour expressed in the Jersey/Hereford female. While it is greater than the average of the two it is still less than the Jersey.
Generally, hybrid vigour will be greatest:
When the parents are genetically most unrelated. A Bos indicus/Bos taurus cross (e.g. Brahman/Hereford) will exhibit more hybrid vigour than a European/British (e.g. Charolais/Angus) cross which will exhibit more hybrid vigour than a British/British cross (e.g. Angus/Hereford).
When appropriate breeds are chosen for crossbreeding. There can also be differences in the amount of heterosis expressed between various breeds. For example, research in Nebraska in 1965 demonstrated that heterosis effects for weaning weight were larger in the Hereford x Angus and the Hereford x Shorthorn crosses than in the Angus x Shorthorn.
In the past, Brahmans were the only breed with traits enabling it to thrive under the harsh environment of Northern Australia. Because of the lack of alternative tropical breeds, Brahman cattle had to be crossed with British breeds. The introduction of the Boran and Tuli has widened the crossbreeding possibilities in Northern Australia.
For traits that are weakly inherited such as fertility, milking ability and longevity. These respond more strongly to crossbreeding than highly-inherited characters such as growth rate. Hybrid vigour is therefore more pronounced for reproductive characters, but it can also lead to improvement in growth rate, feed conversion and calf survival.
Most traits are affected by crossbreeding but not all traits benefit just from hybrid vigour. Muscling and maturity are two traits which are affected by the actual breed used more than by hybrid vigour.
Hybrid vigour can be divided into individual heterosis and maternal heterosis.
Individual heterosis is the increase in growth rate of a crossbred calf. Two straightbred parents produce a crossbred calf which will be about 8.5% heavier at weaning than a straightbred calf.
Maternal heterosis is exhibited by a crossbred cow. A crossbred cow will have higher milk production and be more fertile than a straightbred cow. As a result, her calf will be about 14.8% heavier at weaning than a straightbred calf. These figures are averages, the actual response depends on the breeds chosen.