After decades of phenotypic decline in fertility traits as dairy farmers bred cows to make more milk instead, the industry has more recently seen improvements in heifer conception rate (HCR), cow conception rate (CCR), and early first calving (EFC), as well as modest progress in daughter pregnancy rate (DPR). “Overall, I would say we’re making generally favorable progress,” said John Cole during a Dairy Calf and Heifer Association webinar.
This indicates that selection for these specific fertility traits is working, continued the Council on Dairy Cattle Breeding’s (CDCB) chief research and development officer.
Cole explained that HCR and CCR are both based on confirmed pregnancies, specifically, the percentage of inseminated animals that become pregnant at each service. The DPR trait is based on days open. For example, a 1% higher pregnancy rate is correlated to four fewer days open. He recognized that the CDCB trait assumes a 60-day voluntary waiting period, which is shorter than what many farms use today with their more productive cows.
Every farmer has their own trait preferences to look at when it comes to sire selection, and fertility traits have gained more interest than they once held. While these traits have low heritabilities, making patience in selection efforts valuable for farmers, Cole added the good news that HCR, CCR, EFC, and DPR all have moderate to high genetic correlations with each other.
“The key here is that selection for one fertility trait will generally also result in improvements in the other fertility traits,” he stated.
With multiple fertility trait options, it can be hard to know which one to focus on. Though their correlation with each other is helpful, Cole also advised the use of indices to make the most of this information. “My recommendation as a geneticist is to put them in a selection index,” he said, describing the many different indices available that a farmer could choose to be the best fit for their farm. If this is the route you take, he advised against setting thresholds for individual traits as the index has already taken into account the traits’ correlations.
The genomic support system
We cannot talk about genetic improvement in dairy cattle in the last 15 years without mentioning genomics. Francisco Peñagaricano, an assistant professor at the University of Wisconsin-Madison, said genomics has caused the most significant change in the industry since the introduction of artificial insemination.
Genomics allows us to estimate the genetic value of an animal as precisely as possible. If we don’t use genomic information, our best option is parent average. The reliability of this tool can reach up to about 35%, he said, but it may also be zero. That would be if we have no pedigree information or the wrong information.
With genotyping, we can predict genetic merit with 65% to 80% accuracy, Peñagaricano said. Genomics raises reliability in all traits, but it is especially valuable with lowly heritable traits, such as those for fertility, health, and longevity.
Another option for predicting genetic value without genomics is by analyzing sire predicted transmitting abilities (PTAs), but that also has its flaws. “You are ignoring the cow — half the genome comes from cow,” Peñagaricano emphasized.
A complete estimation of genetic value allows farmers to focus breeding efforts on animals that show the most potential. That not only makes more economic sense in the short term, but it helps the dairy population continue to improve in the decades to come.
