Growing Beef Newsletter
March 2026, Volume 16, Issue 9
Improving weaned calf health through genetics
Audrey Tarochione, animal breeding and genetics graduate student, Iowa State University
Every producer knows that sinking feeling of spotting a calf that looks like he just doesn’t feel good. Even if we use good management practices and cross our fingers, calves still get sick every now and then. Bovine respiratory disease (BRD) is a multifactorial disease caused by a culmination of stress, viral agents, and bacterial infections. Especially relevant to weaned calf health, BRD costs the U.S. feedlot industry approximately $1 billion annually in production losses. Management is key to minimizing the impacts of stress around weaning, but some of these stressors are intrinsic to the beef industry: separation from dam, diet changes, transportation, etc.
There is a genetic component to respiratory health, meaning selection for BRD resilience is possible. In a recent study on calf health in weaned seedstock calves, disease incidence was defined as a binary phenotype, where a calf either remained healthy during the post-weaning period or required one or more treatments for BRD. The heritability of BRD incidence was estimated to be 0.074. As with most health traits, heritability estimates of BRD traits are generally low, but this estimate is still meaningful. Progress will be slow, but over time, permanent improvement can be made in the health of your calves through genetic selection.
Currently there are no BRD EPDs published by breed associations. Multiple challenges contribute to this limitation:
- Loss of data when calves are sold: When ownership of calves is transferred, data is lost, including pedigree and early-life information. The majority of calves are sold less than 45 days after weaning, when they are still at risk of BRD. While feedlots can maintain solid treatment records, this information is not enough to run a genetic evaluation. Pedigree and/or genotype data, in conjunction with phenotypes, are necessary to develop an EPD.
- No phenotyping guidelines: Due to limited research, it is still unclear how BRD should be evaluated. A variety of terminology is used, such as BRD incidence, resilience, number of treatments, and severity. Each of these traits differs slightly in definition, phenotype collection, and statistical analysis. More research is needed to determine the trait that provides the most benefit to genetic improvement.
- Detecting BRD can be difficult: Cattle are adept at hiding illness, making visual detection of sick calves both an art and a science. Even the best pen rider can’t catch all BRD cases in a timely manner. Subclinical BRD is also known to depress feedlot performance. However, these cases go undetected unless lung lesions are scored at harvest. Advances in technology now make it easier to find sick calves. Detection aids, like wearable sensors, can flag BRD cases multiple days before visual observation and pick up a portion of subclinical illness.
This monthly newsletter is free and provides timely information on topics that matter most to Iowa beef producers. You’re welcome to use information and articles from the newsletter - simply credit Iowa Beef Center.
