Bovine Respiratory Disease in Dairy Calves - Diagnostic Tools and Management Practices

Adapted by Betsy Karle, UCCE Glenn, Tehama, Shasta, Butte, Sutter-Yuba, William Love, DVM & Sharif Aly, BVSc,UCD Veterinary Medicine Teaching & Research Center

Pneumonia, more formally referred to as bovine respiratory disease (BRD), is the leading natural cause of death in U.S. beef and dairy cattle, causing the annual loss of more than one million animals and financial losses in excess of $700 million. Control and prevention of BRD is difficult due to the disease's multiple causes and a complex web of interacting risk factors. In addition, there is no standardized field diagnostic method that can be used for early identification of BRD cases. Typical diagnosis and treatment decisions are based on mostly subjective clinical criteria that aren’t good predictors of underlying respiratory system disease. Calves with BRD will present a wide range of clinical signs ranging from severe respiratory distress to asymptomatic. The specific clinical signs presented by calves with BRD are also variable, and there are no clinical signs that always present in affected animals.  This may lead to not detecting cases early in the course of disease, which leads to poor treatment outcomes once detected and suboptimum animal welfare and production.  In contrast, some calves may be falsely diagnosed as BRD cases leading to calves being unnecessarily treated with antibiotics which can contribute to antibiotic resistance and economic losses due to unnecessary treatment costs.

To address these issues, we assembled a team of UC Davis animal scientists and veterinarians, UC Cooperative Extension specialists and farm advisors and veterinarians from California Department of Food & Agriculture to work closely with dairy producers in a 4-year study to unravel some of the mysteries of BRD. One of the first tasks was to develop a diagnostic tool for BRD that is accurate, rapid, cheap, reliable and simple.  Through a statistical analysis of a dataset of 2000 pre-weaned calves (funded originally by USDA, NIFA, BRD CAP), our team identified an on-farm scoring system comprised of 6 clinical signs (Love et al. 2014). Each clinical sign is categorized as normal or abnormal, regardless of severity (hence its simplicity). The clinical signs include nasal discharge (4 points), ocular discharge (2 points), cough (2 points), fever (2 points), breathing difficulty and rate (2 points), and ear droop or head tilt (5 points). For a calf with BRD signs, the sum of points for any of the 6 signs observed is used to determine BRD case status (Table 1).  Calves are considered to have BRD if the sum of the scores is greater than or equal to 5.  The scoring system correctly identified 72.2% of calves with BRD and 89.9% of healthy calves in a follow-up validation study. 

Table 1: Clinical signs and respective scores assigned by the California BRD scoring system for pre-weaned dairy calves.

To consider the scoring system in an even more simplified way, calves with any of the following are likely BRD cases:

• a head tilt or ear droop (score=5),
• nasal discharge plus one other clinical sign (score ≥ 6), or
• any 3 clinical signs (score ≥ 6).

On farm scoring sheets in English and Spanish are in final revisions and will be available soon. The next phase of our research is developing a risk assessment tool for BRD using information on housing, nutrition, and management of calves. The tool will provide valuable information for designing herd-specific BRD control and prevention programs.  We are currently using the California scoring system in our on-farm research to develop this risk assessment tool. Additionally, this work complements genomics work being conducted in an associated USDA study aimed at identifying DNA-based genetic markers associated with reduced BRD incidence in cattle. For more information about this project or if you are interested in being part of the risk assessment study, email brdsurvey@vmtrc.ucdavis.edu or call Betsy Karle (530-865-1156) or your local UCCE Dairy Advisor.

Reference:  Love et al. 2014. “Development of a novel clinical scoring system for on-farm diagnosis of bovine respiratory disease in pre-weaned dairy calves” https://peerj.com/articles/238/