Crossbreeding Breeding Systems
Crossbred pigs have some advantages over purebred pigs because of a genetic
phenomenon called heterosis (also known as hybrid vigor). Because of heterosis, most
commercial swine producers use crossbred pigs rather than purebreds. What is heterosis?
Heterosis usually gives crossbred pigs an improvement over the average of its parent
purebreds in a certain trait.
For example, if the average litter size for a herd of Yorkshire purebreds was 11 and the
average litter size for a herd of Hampshire purebreds was 9, we would expect the average
litter size of Yorkshire x Hampshire crossbred sows to be 10 pigs. In reality, the average
litter size might be closer to 11.5 pigs, which is higher than either of the parent breeds.
Improvement of the actual litter size over expected litter size is a result of heterosis. You
may be able to understand heterosis better be studying the following table.
Yorkshire litter size = 11 pigs per litter
Hampshire litter size = 9 pigs per litter
Expected litter size of Yorkshire x Hampshire crossbred sows = 10 pigs per litter
Actual litter size of Yorkshire x Hampshire crossbred sows = 11.5 pigs per litter
The difference between actual (11.5) and expected (10) = 1.5 pigs per litter is a result of
heterosis.
Generally, heterosis affects reproductive traits relatively more than growth and carcass
traits. Heterosis affects several important reproductive traits in pigs. In addition to
improvements in litter size, crossbred sows usually produce more milk, eat more, and
farrow more vigorous pigs than purebred sows.