Capturing the value of crossbreeding, Rolf, Weaver delve into misconceptions of crossbreeding
“The benefits of crossbreeding fall into two main categories,” says Kansas State University’s (KSU)Megan Rolf. “The first of those is heterosis, and the second is breed complementarity.”
Rolf explains heterosis refers to the advantages in production that producers see over the average of the performance that is expected in two purebred lines, while breed complementarity is matching breeds to complement strengths and weaknesses.
Rolf and Weaver, both of KSU, looked at misperceptions surrounding crossbreeding to debunk myths.
“We often hear heterosis referred to a hybrid vigor,” Rolf explains, “but actually, it’s the superiority of a crossbred animal as compared to the average of its straight-bred parents.”
A larger impact in heterosis can be seen as the difference between parents gets larger, she adds.
“I typically think of heterosis as being derived by alleles from two different breeds paired together in an offspring,” she says. “If we have a Simmental and Hereford cross, the heterosis comes because everywhere we have a Simmental allele, we have a Hereford allele, as well. We see impacts from heterosis.”
Weaver said he commonly hears heterosis only exists in first generation crosses, which is untrue.
Rolf explains, in a second generation cross the impacts may not be as significant, but heterosis remains in about 50 percent of the genome.
“Heterosis is retained in future generations as a result of the alleles from different breeds pairing together,” she says. “The alleles don’t just disappear after the first generation, but the amount of heterosis realized may be different, due to the relationship between different breeds.”
Weaver notes, however, “Research suggests that heterosis is not available within breed matings. Though breeds may be different in terms of genomics, they’re really not different enough in the genetics in terms of alleles to generate heterosis.”
Crossbreeding can result in carcass changes, as well, but Rolf comments it is not in the way people may think.
“If we look at lowly heritable traits, we get a pretty good response in improvement as a result of heterosis,” she says. “Carcass traits fall in the middle somewhere.”
Rolf continues, “However, we know there is more to crossbreeding than just heterosis. Breed complementarity has an impact.”
For those highly heritable traits, breed complementarity can optimize performance levels.
While there are known and recognized benefits of crossbreeding, Rolf said a common misconception of the practice is crossbreeding leads to large increases in birthweights in calves.
Crossbreeding has been the subject of research for many years, and the U.S. Meat Animal Research Center looked at the impacts of heterosis for birthweight, weaning weight and yearling weight data for three crosses – British by British breed, British by Continental and Continental by Continental.
“What we expect is somewhere around half to three-quarters of a kilogram – or a pound to a pound and a half of additional birthweight due to heterosis,” Weaver explains. “We find substantially larger increases for weaning weight and yearling weight.”
He adds, “Those increases in birthweight aren’t very big.”
Best of all worlds
“We can really take advantage of both heterosis and breed complementarity in our different mating systems,” Rolf comments. “We can focus on increasing genetic merit through EPDs but also adding mating systems to take advantage of the benefits of heterosis.”
Rolf continues, seedstock producers should focus primarily on the additive genetic merit, while commercial producers can choose their best plan.
Weaver adds an understanding of whether the benefits of straight breeding outweigh the improvement of traits that might be gained via heterosis for each operation should be considered.
“To get the most value out of these systems – heterosis and breed complementarity, we need to put them together and utilize the selection tools in terms of EPDs and indexes and breeding system design to capture the heterosis piece,” Weaver comments.
Saige Albert is managing editor of the Wyoming Livestock Roundup. Send comments on this article to firstname.lastname@example.org.