|
Bovine Respiratory Disease Complex Undifferentiated bovine respiratory disease complex (BRD) or "shipping fever" is one of the most economically important cattle diseases in the US, accounting for up to 31% of cattle deaths. Pneumonia accounts for up to 10% of deaths in beef calves and 24% of deaths in dairy calves in the US. However, the percentage of deaths from respiratory disease affecting post-weaning calves increases dramatically, ranging from 45-64%. The complex of diseases may be managed on the farm with the key focus on prevention of respiratory diseases, rather than treatment. Clinically affected cattle are inidicative of an overall herd health problem, as most of these diseases are subclinical (there are no overt signs of disease such as coughing, nasal discharge, inappetance, etc.). Signs of clinical disease include the following: - moist or dry cough
- labored breathing
- abnormal sounds heard when breathing
- exercise intolerance
- nasal discharge
- dirty nose
- foul breath
- cynosis (blue) gums
- depression
- isolated separately from herd
- poor appetite
Upon physical examination, the following findings are common: depression, fever, ocular and nasal discharge, anorexia, weight loss, rapid/shallow/painful breathing, moist coughing especially when moving, labored breathing during the terminal stages. In feedlot calves, signs of BRD occur 6-10 days after exposure. In dairy herds, enzootic calf pneumonia is seen 3-10 days after exposure and usually affects multiple individuals. Clinical signs include fever, cough, nasal discharge, open mouth breathing, dehydration and poor appetite. If the clinical signs do not resolve after 10-14 days, the calf can be chronically affected and be a "poor doer". Steps leading to BRD in a herd: - stress and upper respiratory viral infection
- proliferation of bacteria normally present in the upper respiratory tract
- failure of the tracheal cells to normally clear the lungs
- proliferation of normal nasal bacterial flora from the upper respiratory tract in the lungs
- infectious inflammation of the ventral lung
Organisms of importance in BRD include bacterial, viral and parasitic agents. 1. Bacteria - Mannheimia (Pasteurella) hemolytic A1 is the most important bacterium
- Pasteurella multocida
- H. somnus
- A. pyogenes
- Bacterioides spp
- S. aureus
- Streptococcus spp
- E coli
- Klebsiella
- Salmonella spp
- Mycoplasma spp
- Chlamydia spp
- Ureaplasma spp
2. Viruses - Adenovirus
- IBR or BHV-1
- BHV-4
- BRSV
- PI3
- Rhinovirus
- BVD
- Reovirus
- Enterovirus
3. Parasites The most common bacterial pathogen isolated from the respiratory tract of cattle with BRD is Mannheimia hemolytica serotype A1, which is part of the normal flora of the tonsils. The bacterium spreads easily between calves and proliferates when calves are stressed, secondary to viral upper respiratory infections and when silage is fed. When bacteria invade the lower respiratory tract (lungs) and are not able to be cleared out due to a defective mucociliary clearance mechanism secondary to viral infection, white blood cells invade the lungs. Bacterial leukotoxins kill the white blood cells; the substances released secondary to the death of the white blood cells result in lung tissue damage, fluid accumulation and accumulation of more white blood cells. This vicious cycle results in damage to lung tissue. When an acute outbreak of BRD occurs, a necropsy is one of the most important diagnostic tools that your veterinarian can perform. Visualization of damage to the lungs as well as obtaining diagnostic samples for bacterial and viral culture and identification are performed. Ideally, early detection of cattle affected with BRD are performed prior to permanent lung damage. Use of an appropriate antibiotic effective against the organism causing clinical signs is necessary, at an appropriate dose and for an appropriate duration. Rest, nutrition and rehydration are key components of supportive care. When treating cattle with antibiotics, it is important to remember that some antibiotics have potentially fatal effects. Micotil administered IV will kill cattle and injection of humans by any route may be lethal. Management of young cattle is essential in reducing the risk of BRD. Adequate passive transfer of immunoglobulins via a sufficient amount of good quality colostrum is essential. Adequate nutrition, ventilation and protection from environmental factors is also a factor in reducing the risk of exposure to BRD. Avoid overcrowding, mixing wide age ranges and be knowledgeable about the source of calves if purchasing them. A proper preweaning vaccination program and preconditioning will significantly reduce cases of BRD in the feedlot. Reducing stress is one of the most important components of managing BRD. In addition, vaccination guidelines should be formulated for each herd based on the risk of exposure to disease. Killed and modified-live vaccines (MLV) are available for preventing BRD. Killed vaccines are less immunosuppressive and may be administered to pregnant cattle; however, they require a booster dose, have a higher cost, have a narrower spectrum of protection against diverse strains of viruses and have a shorter duration of protection. MLV require a single dose to be protective, making them less expensive and have a longer duration of protection. However, they are ineffective if inadequately stored and mixed, may cause disease in stressed animals and may cause abortion in pregnant animals. Setting up a vaccination protocol upon recommendations by your veterinarian is an important component of managing BRD.
|
