Pneumonia - Bovine Respiratory Disease - Dairy (BRD)
Pneumonia. Bronchial pneumonia. Fibrinous pleuropneumonia. Shipping fever. All of these terms describe the same costly disease: Bovine Respiratory Disease complex, or BRD.
BRD a major cause of economic losses to the Dairy Industry. Depending on the organism(s) involved, death from BRD can occur within 24 to 36 hours of symptoms appearing, or the infection can become chronic, not causing death but instead producing widespread, permanent lung damage. Once the disease has progressed to the point that fibrosis, adhesions and/or abscesses have developed in or around the lungs, no treatment will satisfactorily correct the problem. The animal may survive, but it will always carry some residual lung problems that will impact performance. That is why early recognition and treatment of BRD are so important.
BRD is defined as a "disease complex" for two reasons:
- It usually is caused by a variety of pathogens, both viral and bacterial, that interact with one another to produce full-blown disease, and
- The behaviour of these pathogens follows a sequential process that, step by step, results in sick animals.
Bacterial pathogens apparently cause the acute syndrome by invading the bovine respiratory tract that has been compromised by viral infections. Preceding and contributing to the infection is the stress of weaning, change of feed and variations in ambient temperature and humidity, all of which tend to reduce energy reserves.
Several species of bacteria have been isolated, but the most commonly found species are Mannheimia haemolytica. (formerly known as Pasteurella haemolytica), P. multocida, Histophilus (Haemophilus) somnusand Mycoplasma spp. From all observations and experimental evidence, M haemolytica. (P. haemolytica) and P. multocida are the most important bacteria involved in BRD.
Viruses such as Infectious Bovine Rhinotracheitis (IBR), Bovine Viral Diarrhoea Virus (BVDV), Bovine Respiratory Syncytial Virus (BRSV) and Parainfluenza Virus 3 (PI3) may also be involved in the BRD complex, often opening the door to secondary bacterial infections.
Clinical Signs and Diagnosis
BRD manifests in numerous ways in dairy cattle, depending on the age of the animal, causative organism(s) and stage of the disease, among other factors. While identifying sick dairy cows is not an exact science, producers should be trained to watch for these early clinical signs:
- Fever.The connection between BRD and fever is extremely strong. BRD is one of the most common causes of fever - and fever is one of the earliest signs of the BRD complex.
- Depression. Affected animals hang their heads, look lethargic and often stand away from other cattle.
- Inappetence. An animal's unwillingness to eat is tied closely to fever and depression. A "floppy" belly, caused by a shortage of fibre in the digestive tract, is an early sign of inappetence.
- Serous nasal and eye discharge. One of the earliest indicators of BRD, this form of discharge is watery, sticky and clear. Serous discharge usually starts from the nose, then moves to the eyes as the disease progresses.
- Purulent nasal discharge. An indicator of more advanced BRD, this discharge is thick, cloudy and pus-filled. The cloudy appearance is caused by white blood cells that have localised in the respiratory tract to attack the infection.
- Bloody nasal discharge. Also in acute BRD cases, blood may appear in the nasal discharge due to irritation in the respiratory tract. The protective mucosal lining is broken down and enters the respiratory system, where it is blown out.
- Stiff gait. Sick animals may experience muscle and joint soreness due to an increased systemic endotoxin load, similar to a person with a bad case of flu. Their movement indicates overall ache.
- Crusty muzzle. Because it is not feeling good, the animal will tend to lick its hair and muzzle less and generally take poorer care of itself. At the same time, mild dehydration will cause a drying of membranes around the mouth, adding to the dry, crusty appearance.
- Salivation. Again, the animal's overall feeling of malaise may cause it to drool and gape more than usual.
- Mild diarrhoea. Endotoxins in the animal's system cause displacement of body fluids, dumping more fluid into the bowel and disrupting normal absorption of food, causing loose stools.
- Rapid, shallow breathing. More blood is distributed to the infected portion of the lungs, causing occlusion of airflow. The animal has to breathe harder to get good air exchange, because parts of its lungs are not working properly. Early morning, when environmental influences are less, is the best time to evaluate breathing. Increased respiration when the environmental temperature is high may be caused more by the external environment than disease. On the other hand, a calf breathing 60 breaths per minute at 5 a.m. when the ambient temperature is low is truly ill.
- Soft coughing. In early BRD cases, the lungs and airways are generally painful, so the animal will try to clear the airway with mild, tentative coughing. Loud, prominent coughing or "honking" indicates far more chronic, advanced cases, at which point treatment is difficult.
There is no miracle answer to effectively managing BRD. Because it's a disease complex, determining the right treatment for each individual case is a complex process as well.
When addressing a severe BRD challenge, here are a few evaluation tools to help you improve how you manage the disease complex:
- Identifying fever. To catch fevers in freshly calved dairy cows, taking temperatures for the first 10 days post-calving is recommended. The first 10 days post-calving have the highest percentage of fevers. The cow is under high stress, including giving a lot of her own immune defenses to her calf in the colostrum.
- When checking these Cows, it is recommended to take temperatures in the early morning to avoid elevations solely due to high ambient temperatures.
- Complete blood count (CBC). Blood is a window into the body. A CBC on one or a handful of cows can be helpful in determining to what stage the disease has progressed, and sometimes what main, causative organisms are involved.
- Necropsies. Taking a look inside a dead animal can help evaluate what organisms are involved and how various treatments are working. The more history available on the dead animal, the better. For example, knowing when the cow got sick, what its temperature was, what she was treated with and when she was last treated will help make visual evaluation of her lungs more meaningful.
There are a number of injectable antibiotics available for treating pneumonia and reducing fever caused by BRD infections. Selection criteria should include:
- Milk Safety. Consumer pressure makes milk safety more important every day. A heightened commitment from veterinarians and producers has improved the dairy industry's ability to produce safe, high-quality dairy products that are good value to the consumer.
- Speed of Action. Your antibiotic should penetrate blood and tissue rapidly.
- Spectrum of Activity. The most effective antibiotics are active against all three of the major BRD pathogens - Mannheimia haemolytica. (formerly known as Pasteurella haemolytica), Pasteurella multocida and Histophilus (Haemophilus) somnus.
- Mode of Action. Bacteria that cause pneumonia or BRD do not actually reside in the cells of the cow's lung tissue. Rather, they are located outside the host's cells in the fluid surrounding the cells inside the lungs. Effective antibiotics must concentrate in this extracellular fluid.
- Susceptibility. Practitioners and dairymen work together to make sure that resistance does not reduce the effectiveness of today's most powerful antibiotics.