Invited review: crossbreeding in dairy cattle: a Danish perspective.

The value of crossbreeding in livestock species has been known for a long time; it has been used heavily within beef cattle, pig, and poultry production systems for several decades. This has not been the case for dairy production but lately there has been increased interest in crossbreeding dairy breeds. This review focuses on the practical and theoretical background of crossbreeding and describes the gain to be expected using systematic crossbreeding in dairy production. In Denmark, 24% of dairy farmers would consider starting crossbreeding programs within their herd. Evidence for the value of crossbreeding is documented with special emphasis on results from a Danish crossbreeding experiment. This experiment included 1,680 cows from 3 breeds and their crosses. In general, at least 10% heterosis can be expected for total merit, mainly due to increased longevity and improvement of functional traits. A minor part of heterosis for total merit is due to heterosis for production traits. For production, there is evidence of recombination loss using continued crossbreeding programs, which does not seem to be the case for longevity and total merit. However, recombination loss should be investigated more carefully as crossbreeding is becoming more popular. A prerequisite for crossbreeding to be beneficial on a long-term basis is that genetic gain within the parental breeds not be reduced. As long as the crossbred cow population constitutes less than 50% of the whole population, and young bulls can be tested through crossbred offspring, this prerequisite can be fulfilled. Crossbreeding can increase dairy income substantially, especially in management systems requiring a high level of functional traits.