Bovine respiratory disease (BRD) is arguably the most economically significant health concern for the beef cattle industry. Shipping Fever, respiratory disease complex and pneumonia are all common synonyms used to describe BRD. Given its significance, there is a wealth of information available regarding the condition. The purpose of this article will be to provide a general overview and a basic understanding of BRD and the diagnostic and treatment tools available to cattle producers as well as currently recommended prevention strategies.
Most cases of respiratory disease that cause overt clinical signs in cattle and potentially end in death of the animal are bacterial pneumonias. Mannheimia and Pasteurella species are the most common bacteria isolated from the bovine lung with pneumonia. Other bacterial infections can result in pneumonia and pure viral pneumonias do exist but these both occur less frequently. Rarely, respiratory disease is caused by another physiologic mechanism altogether, but for the purpose of this article, our focus will remain on bacterial pneumonia.
Mannheimia and Pasteurella organisms are normal residents of the nasal cavity of the bovine. Normal immune function in healthy animals prevents overpopulation of these organisms and defends the animal from disease. However, when normal immune function is compromised, bacterial colonization often occurs, leading to clinical pneumonia.
Younger cattle with little natural immunity are most susceptible to infection. While bacterial pneumonia is our focus, viral infection often precedes bacterial infection by suppressing normal immune function, and therefore deserves some recognition. The viruses of interest are well-known and include Bovine Viral Diarrhea Virus (BVD), Infectious Bovine Rhinotracheitis Virus (IBR), Bovine Respiratory Syncytial Virus (BRSV) and Parainfluenza-3 Virus (PI3). These viruses can cause other diseases in cattle including abortion and are part of routine vaccination protocols for cows and calves. In addition to concurrent viral infections, other factors that predispose calves to BRD include stress from weaning, hauling, weather or processing. Heavy pathogen exposure encountered during commingling or during sale can also lead to BRD. Lastly, and less commonly, poor ventilation or poor air quality can result in respiratory tract irritation leading to infection.
Prevention of BRD is aimed at effective vaccination against viral and bacterial organisms and minimizing stress and pathogen exposure. Preconditioning programs have proven to reduce morbidity and mortality from BRD in beef calves. Consistent with most preconditioning programs, I routinely recommend initial vaccination and processing (castration, dehorning, etc.) 30 days prior to weaning with booster vaccinations at weaning for all producers regardless of herd size. Weaning calves for 45 days prior to shipping and commingling will further reduce stress at the time of greatest pathogen exposure. For producers who can document these practices, calves can be sold at value-added sales for a premium price. Because preconditioning programs are gaining in popularity, cow-calf producers are more effectively offsetting the additional production costs and realizing a profit for their preconditioned calves. Metaphylaxis, or treatment of all calves with an antibiotic at processing, is a good preventative measure for use in high risk calves.
If all preventative measures fail, or in those calves in which prevention strategies are not utilized and pneumonia sets in, producers should be prepared for prompt diagnosis and effective treatment. We will discuss these topics in the next issue.
Darren Loula, DVM, is a large animal veterinarian at Fair Grove Vet Service in Fair Grove, Mo.
