When crossbreeding started picking up steam in U.S. dairy herds, the genetic toolbox wasn’t really built for the cows’ producers had in their barns.
Genetic evaluations worked well for purebreds, but for Holstein–Jersey crosses and other combinations, the system only went so far and accuracy dropped. That gap is what the Council on Dairy Cattle Breeding (CDCB) set out to address.
In a recent episode of the CDCB Cow Cast, George Wiggans, longtime USDA research geneticist and current CDCB technical advisor, walked through how genomic evaluations and Breed Base Representation (BBR) have changed the way crossbred dairy cattle are evaluated.
Why Crossbreds Didn’t Quite Fit
For a long time, dairy genetic evaluations were built around purebred populations, which worked well when most herds were fairly uniform and selection stayed within a single breed.
Evaluations were done within each breed, so crossbred animals didn’t always line up as well in the system and their results were less accurate. As crossbreeding became more common in commercial herds, especially in Holstein–Jersey systems aimed at balancing production and components, those gaps became more noticeable. The system could still generate numbers, but they didn’t always reflect what was happening in mixed-breed cows.
Meanwhile, the industry’s data foundation was still developing. For decades, most genetic progress came from what Wiggans calls the basics.
“We still relied on traditional evaluations, which pulled together data from farms across the country and even around the world to figure out which animals perform best,” Wiggans says. “Then we would take all that information across the traits we measure and combine it into a profile or index that would help predict how profitable an animal would be.”
That system has long been used in dairy genetics, but it didn’t always handle animals with mixed-breed backgrounds as smoothly.
Genomics Opens the Door
Genomics changed how geneticists approach evaluations. Instead of relying only on performance records, the system now uses DNA to connect specific parts of the genome to trait outcomes.
Wiggans says this is done using what are called reference populations.
“The concept is that by having a large reference population, we can assign genetic values to these segments of the chromosome,” Wiggans says. “So, when we put it all together and add it all up, we can say, we think that this is going to be the cow’s productivity for each of the traits we analyze.”
He explains genomic evaluation as building a kind of genetic mosaic, where pieces of DNA get value based on data from large groups of known animals. This worked well for purebreds, but for crossbreds there was still a missing piece: a consistent way to describe breed makeup in a way national evaluations could use directly.
BBR Gives Crossbreds a Place
To address that gap, the industry developed Breed Base Representation, or BBR.
“Recognizing that we would like to extend the genomic evaluations to crossbreds, we needed some way of identifying what the breed background was of an animal,” Wiggans says.
BBR uses genomic data to estimate how much of each breed is in an animal.
“We used kind of an interesting approach here… Why don’t we use the same idea to estimate how much Holstein, Jersey, Guernsey, and other breeds are in an animal,” Wiggans says.
Purebred animals serve as the starting point because their genetics are clearly defined.
“We treat a purebred animal as fully belonging to its breed, like giving it a ‘1’ for that breed and a ‘0’ for all other breeds,” Wiggans says. “Then we use genetic markers, called SNPs, to estimate how much of each breed is in mixed animals.”
From there, each animal gets a breed breakdown.
“So, an animal could be 75% Holstein and 25% Jersey,” Wiggans says. “That’s what Breed Base Representation, or BBR, reports.”
BBR breaks an animal’s genetics into breed percentages, giving producers a clearer way to understand and compare crossbred animals. He adds that the approach is considered highly accurate because it’s based on large amounts of genetic data from many animals.
Putting Breed Mix into One Number
BBR describes what breeds are in an animal. The next step is turning that information into a usable evaluation.
“By having this BBR that we’ve discussed, we can say, well, let’s just do a weighted average,” Wiggans says. “We’ll multiply each evaluation by the percent of each breed that it is, add it all up, then that will be our evaluation of this animal.”
Each breed contributes to the final score based on how much of that breed is in the animal. A higher percentage of a breed means it has more influence on the outcome. The final result is one evaluation number for crossbred animals that reflects their actual genetic makeup, instead of forcing them into a single-breed category that doesn’t fully represent them.
Crossbreds are Now Part of the System
As genomic testing has expanded, crossbreds have become a bigger part of the national dataset.
“So, not surprisingly, Holstein numbers were over 9 million last year, with Jersey coming in second,” Wiggans says. “But what stands out is that crossbreds are now the third largest group. So, providing evaluations for crossbred met a real need in the industry.”
Today, crossbred animals are included in the evaluation system. Tools are now in place to better reflect how they are bred and managed on today’s dairies. As genetic evaluations continue to evolve, Wiggans expects crossbreds to remain part of the picture.
“We’re working on strategies to take this into account so that the evaluation simultaneously considers both the genetics and her traditional data,” he says. “We expect that we’ll still offer evaluations for these animals, so that the BBR will continue to have a role in the evaluations.”
The result is a system that better matches the cows’ producers are working with every day, bringing crossbreds fully into the genetic conversation.
