Causes and Risk Factors
A general term for respiratory disease in cattle, BRD is often called a “disease complex” because many factors can contribute to its development and progression, including:
- Stress from weaning, castration, dehorning, transport, commingling, poor ventilation and overcrowding can compromise an animal’s immune system, making it vulnerable to viruses and bacteria.
- Viruses such as bovine respiratory syncytial virus (BRSV), parainfluenza 3 (PI3), bovine viral diarrhea (BVD) virus, infectious bovine rhinotracheitis (IBR) virus and bovine coronavirus (BCV) can further compromise the respiratory tract.
- Bacteria including Pasteurella multocida, Mannheimia haemolytica, Histophilus somni and Mycoplasma bovis may exacerbate the problem.
- Parasites and fungi such as lungworm and Aspergillus also can damage the respiratory system.
- Weather or temperature fluctuations can increase the risk of BRD as well.
The signs of BRD may vary depending on the animal’s age, the organisms involved and the severity of disease. BRD can affect the upper respiratory tract, causing inflammation in the nasal passages, trachea and bronchi, the airways leading to the lungs. Pathogens also can invade the lower respiratory tract, or the lungs, causing pneumonia. Calves may stand with ears drooping, heads and necks extended and their backs bowed in an effort to breathe. Other signs include:
- Rapid, shallow and/or noisy breathing
- Nasal and/or eye discharge
- Loss of appetite
- One of the earliest signs of BRD, calves often have a rectal temperature over 104° F.
- A soft cough may be elicited when the animal is disturbed.
- Rapid, shallow and/or noisy breathing:
- In severe cases, animals may grunt on expiration.
- Nasal and/or eye discharge:
- The discharge may be clear or white tinged with green or yellow.
- Loss of appetite:
- Careful observation can help detect individual animals that are off feed.
- Animals may lower their heads and ears, move slowly, isolate themselves and fail to respond to pen checkers.
- Death can occur within 24 to 36 hours after the onset of clinical signs.
A presumptive diagnosis of BRD is often made based on signs, the physical exam and disease incidence in the herd. Early detection is important so affected calves can be isolated in the sick pen. In many cases, an antimicrobial may be administered before disease-causing bacteria are identified to get the animal on the road to recovery as soon as possible.
An accurate diagnosis is important because many conditions have similar signs and can be mistaken for BRD, including:
- Allergic pneumonia and nasal inflammation
- Pulmonary edema/heart failure
- Pleuritis (inflammation of the lung lining)
- Pulmonary fibrosis (damaged or scarred lung tissue)
Get the correct diagnosis for BRD. (click to learn more)
Which diagnostic procedures are helpful?
- Nasal swab
- Not always useful. Some bacteria or viruses may be normal inhabitants of the nasal passages, so identification doesn’t necessarily mean there’s an infection.
- Transtracheal wash or bronchoalveolar lavage
- Good choice! A tube is inserted into the trachea and a specimen is obtained from the trachea, bronchi or lungs. This sample can be used to identify bacteria, viruses and lungworms.
- Blood samples
- Good choice! While these tests can help identify antibodies to the bacteria or viruses, some may require several weeks before results are available.
- Good choice! Physical and microscopic examinations can help identify disease agents, and samples can be taken for other tests. Some viruses may only be present early in the disease.
Which laboratory tests are helpful?
- Bacterial culture
- This test helps identify the exact bacteria that may be involved, but it may take days to weeks to obtain results.
- Antimicrobial sensitivity
- Once bacteria have been identified, this test helps determine which antimicrobials will be most effective.
- Virus identification
- This test may not assist with the current BRD outbreak, but helps identify viruses on the operation so appropriate vaccines can be administered in the future.
How are pathological (disease-related) findings used?
- Gross pathology
- Signs of disease that are visible with the naked eye.
- Signs of disease that are visible with a microscope.
In both cases, the lesions can vary depending on the infectious agent and the disease duration.
To help prevent BRD, work with your veterinarian to build a comprehensive program that includes:
- Effective colostrum management to help support immune function
- Vaccination with products that target the most likely viruses and bacteria
- Deworming, especially for areas affected by lungworm
- Proper nutrition including a balanced ration with proper levels of vitamins and minerals
- Other preconditioning strategies such as weaning, castrating and dehorning calves at least 30 days before shipping
- Rest after shipping, keeping food and water within easy access
- Avoidance of commingling animals from different sources
- Stress reduction by minimizing animal handling, pen movements and overcrowding
- Proper ventilation to reduce dust and fumes and reduce heat stress when possible
- Good hygiene including clean, dry bedding
Your veterinarian also can recommend effective antimicrobials for BRD control on arrival and BRD treatment. To ensure that antimicrobials are used responsibly, your veterinarian will consider the product’s:
- Spectrum of activity
- Mode of action
- Duration of action
- Withdrawal period
Zoetis Technical Services veterinarians can provide you with expert advice and tips to help you manage BRD more effectively.