Heart failure has been emerging as an increasingly important disease in feedlot cattle. There are many causes of heart failure in cattle, including exposure to low oxygen levels at high elevations, bacterial infections of the heart muscle and toxins that affect cardiac function. This article is about heart failure observed in feedlot cattle that is not attributable to one of the known causes. This form of heart failure is often referred to as bovine congestive heart failure (BCHF) and it is a major contributor to the increase in heart failure cases seen in feedlot cattle.
Joe Neary and others published a study using health records from a large population of feedlot cattle showing that cases of BCHF had almost doubled over the 12-year span of the study. A common theme gleaned from many interactions with feedlot owners, managers and employees has been the consistent presence of BCHF cases in groups of cattle from particular sources across many years. This theme strongly suggests genetics could play a role in the development of BCHF. In addition, genetics is known to play a strong role in heart failure in other animals, from humans to mice.
Finding a genetic link
To discover if genetic risk factors were contributing to BCHF, we partnered with feedlots to collect samples from BCHF cases. A careful post-mortem exam was conducted on each case to confirm the diagnosis of heart failure and to rule out as many of the known causes of heart failure as possible. DNA samples were collected from confirmed cases and from a healthy calf from the same pen, from the same source, with the same breed type and of the same sex. This matched case-control design was used to help ensure that each pair of animals had similar environmental exposure to disease-causing conditions, as well as being from similar genetic backgrounds.
In that scenario, genetic differences between the case and control could be related to the development of BCHF. In total, 102 case-control pairs were enrolled from four different feedlots and more than 30 unique sources. A genome-wide scan with more than a half-million markers revealed that two major genetic risk factors were associated with BCHF in feedlot cattle. These risk factors were associated with two different genes in cattle: ARRDC3 and NF1A. The odds of BCHF were eight times higher in calves with either of the two genetic risk factors compared to calves with neither risk factor. The odds of BCHF were 28 times higher in calves with both risk factors compared to calves with neither risk factor.
To confirm this result, new samples of 171 BCHF cases and 96 calves with bovine viral diarrhea virus persistent infection (unrelated to BCHF) were analyzed and showed similar results. A panel of A.I. sires representing 99% of U.S. cattle germplasm was used to estimate the frequency of these risk factors in different breeds of cattle. Angus, Red Angus and other British breeds had higher frequency of these risk factors compared with other breeds of cattle. (Visit Association of ARDC3 and NFIA variants with bovine congestive heart failure in feedlot cattle for more information.) It is important to note that the cattle in this study were selected from feedlots in western Nebraska and eastern Wyoming and may not be perfectly representative of cattle in other feeding environments.
Preventing and managing BCHF
One important way to manage BCHF risk in feedlot cattle is to reduce the risk in their parents by selective breeding. Both risk factors seem to require a homozygous inheritance pattern, meaning that cattle need two copies of the bad version of the gene to be at increased risk of developing BCHF. Cattle with only one copy will be carriers but do not appear to be at risk for developing BCHF themselves. By selecting bulls that are homozygous for the good version of both genes, offspring from those bulls will only be carriers and be in the lowest risk category for BCHF regardless of the status of the cow. Through consistent use of homozygous “good” bulls, the number of copies of the risk factor in the herd will be reduced over time. The challenge to this approach is patience and identifying prospective bulls with the desirable genotypes. If ranchers are interested in maximizing genetic progress for BCHF, females can be genotyped to create breeding groups with appropriate bulls to reduce risk more rapidly and to create breeding stock free of BCHF risk factors.
Cattle feeders have fewer options to mitigate BCHF in cattle arriving at their feedlots. Some feedlots have considered genotyping incoming feeder cattle to measure BCHF risk. This approach is challenging for several reasons. Genotyping requires labor, time and financial investments that are often difficult to justify at the feedlot level.
For cattle producers who have a cow-calf operation, feed their own cattle or retain ownership and experience BCHF in their own calves, genotyping of sire candidates can be used to select bulls to rapidly reduce the genetic risk of BCHF in subsequent calf crops. More information on BCHF and testing for BCHF risk can be found online (USDA - Bovine congestive heart failure in feedlot cattle).
