Crossbreeding and hybrid vigour

Heterosis/hybrid vigour is the tendency of a crossbred animal to have qualities superior to that of either parent but not more than the dominant breed.

The graph shows how heterosis can be applied to all health or production traits if there is sufficient genetic difference between the two chosen breeds.

If breed 1 was crossed with breed 2, the green area of the crossbred would be the logical average animal produced. The purple area on top of this is the added benefit, or heterosis, effect. The heterosis effect is variable between breeds and also the traits affected.

Trial work has shown the main benefit of heterosis is seen in fitness and health traits. Around 10-18% heterosis was recorded in trials in California and New Zealand in a wide variety of crossbred cows including Swedish/Norwegian Reds (SRB), Brown Swiss, Jerseys, and Montbelliarde. Milk production has been recorded as improving by up to 6% but it is important to remember this is not the only measure of profitability.

To gain and maintain the effects of heterosis, breed and bull selection is paramount. To maximise the benefits, farmers need to plan the long-term direction they want their business to ensure cross breeding is the right path for them. 

The Spring Calving Index (£SCI) and Autumn Calving Index (£ACI) are designed to make selecting sires for crossbreeding easier.  Farmers who are spring or autumn-block calving should use these as initial filters to compare all bulls of interest then narrow down on the traits they wish to improve within their herd.  The £ACI should be used by all-year-round farmers looking to crossbreed.

• 2 Way Cross - 67%
• 3 Way Cross - 85%
• 4 Way Cross - 94%

Although working a four-way cross system provides maximum gain from heterosis, it is widely recommended a three-way cross is more sustainable. Issues of using a four-way cross include:

• Difficult to implement
• Choosing four suitable breeds can be a problem
• Breed qualities are watered down with each cross

Heterosis should not be used as the main reason to crossbreed but as an added bonus. It is important to remember that crossbreeding is about herd improvement, not breed improvement.

Genomic testing for crossbreeding is currently in development and is expected to be released in 2025.

Crossbred genomics will allow for any combination of crossbred animal to be evaluated under a single-step model. Genomic evaluations will have reliabilities exceeding those of parent averages, improving the accuracy and effectiveness of heifer and bull selection.

Crossbred genotypes currently submitted to AHDB through genomic testing will be evaluated on release of the crossbred national evaluation.