Crossbreeding – Heterosis or hybrid vigour, is the desired result from mating animals of different strains or breeds to improve an animal’s characteristics. These characteristics may include longevity of an animal, production and fertility. Heterosis is a tendency of such a crossbred animal to possess superior qualities to those of either parent but without surpassing the dominant breed in the pairing.
Gaining the positive effects from crossbreeding
If a farmer is looking to improve his or her stock, the selection of the breeding bull and also the breed must be given careful consideration to ensure that the effects of heterosis will be maintained. The farmer needs to have a long-term plan for the direction the herd will take in order for crossbreeding to be a success. Selection of the bull for improving traits should be made using any available data and relevant genetic indexes, such as Profitable Lifetime Index or the Profit Index. Heterosis should not be used as a cure-all for any problems that may be inherent within the herd.
The benefits of crossbreeding
There has been extensive research carried out in New Zealand and the USA which tends to show that heterosis benefits health and fitness traits over profitability traits such as milk production in a dairy herd. The research was carried out using a range of crossbred animals including Jerseys, Brown Swiss and Swedish/Norwegian Reds. Percentage increases in particular traits were recorded at 18 percent for health traits, 10 percent for fitness traits and 6% improvement in production of milk from crossbreeding. These are the rates associated with the heterosis effect but it should be remembered that profitability of a herd is not only measured by milk production and so other profitability measurements should be considered.
How many crosses
The maximum gains obtained from heterosis appear in the four-way crossbreeding system, coming in at 94%. However, the industry recommendation is for three-way crossbreeding. The reasoning behind this recommendation is that for every breed cross, the quality traits of that breed reduce; selecting four complementary breeds can be difficult; and implementing the four-way cross is technically difficult. The three-way cross results in 85% heterosis and the two-way cross results in 67 percent.
The cattle breeding industry does not recommend the use of heterosis as the main driver for introducing crossbreeds into a herd. Crossbreeding should be used as a method of improving a herd over the long term and not as a means of improving the breed in particular.