by Nolan R. Hartwig, DVM, Department of Veterinary Diagnostic & Production Animal Medicine, Iowa State University

Studies show that 65% of the disease-associated losses in feedlot cattle are due to bovine respiratory disease complex (BRDC). Morbidity, the percent of cattle that get sick, can vary from zero to 100%. Death loss ranges from zero to 35% or higher. Respiratory disease includes shipping fever, and a variety of that can occur at any time during the feedlot period, but the highest incidence by far is during the first 28 days in the feedlot. Many cases of so-called "sudden-death syndrome" are actually pneumonia that is easily diagnosed when a post mortem examination is performed.

Costs of BRDC vary significantly. An Iowa State University study showed the average case of BRDC costs $57.48.1 These losses are due to mortality, cost of treatment, reduced performance and increased time on feed. The effects of BRDC on feed efficiency are difficult to measure unless cattle are fed in individual pens.

Respiratory disease probably has the greatest implications for Beef Quality Assurance of all cattle diseases. Injection site lesions are often caused by treatment for BRDC or by preventive vaccinations. Drug residues, although rare in feedlot cattle, may be due to treatment of respiratory disease. Chronic pneumonia and other respiratory problems can lead to lesions that must be trimmed and removed, reducing carcass value. Pneumonia with secondary effects is a leading cause of carcass condemnation at slaughter.

Bovine respiratory disease is caused by a complex interaction of the animal, its environment, and several viral and bacterial organisms. BRDC is commonly diagrammed as follows:

Stress + Viruses + Bacteria = BRDC

Stress is a term that is difficult to define. From the perspective of cattle health, it is best to define stress as a reaction to change. Change includes diet, environment, water, air quality, and other factors. Fatigue, pain, fear and excitement, confinement, lack of access to water, hunger, truck exhaust fumes, rapid diet change, acidosis, mud, heat, dust and perhaps most important of all — weaning, are common stresses. Almost all feedlot replacements experience some degree of stress as they move from cow/calf herds or backgrounding operations to the feedlot environment.

Several viruses are major pathogens involved in bovine respiratory disease. They are highly contagious and include:

1. Infectious Bovine Rhinotracheitis (IBR) or Bovine Herpes Virus-1 (BHV-1) is commonly isolated from cattle with respiratory disease. It causes mild to severe respiratory infection and leads to increased susceptibility to bacterial organisms such as Pasteurella haemolytica. Effective vaccines are available for IBR.

2. Bovine Virus Diarrhea (BVD) is a major feedlot pathogen and is widespread in the cattle population. BVD is a complex disease that exists in many forms. Despite its name, BVD contributes significantly to the incidence and severity of respiratory disease. It suppresses the immune system and increases susceptibility to other pathogens. Its presence in respiratory disease episodes may be subtle unless vigorous diagnostic efforts are made. Vaccination programs help control this disease.

3. Parainfluenza-3 (PI-3) is a common, but mild, upper respiratory infection. It causes inflammation of the upper respiratory tract, mild fever, and increases susceptibility to bacterial infection. Effective vaccines for PI-3 are available, and are usually given in combination with IBR.

4. Bovine Respiratory Syncytial Virus (BRSV) invades the lung, causing a breakdown in lung tissue somewhat similar to emphysema. It can cause explosive outbreaks, resulting in fever and rapid respiration. Mortality can be high. A persistant, dry, hacking cough may indicate BRSV infection. Both killed and modified vaccines are available for BRSV.

5. Several viruses, including rhinovirus, adenovirus, and others, may be present in BRD episodes. Their precise role is unknown. Currently, no vaccines are available for these viruses.

Several major bacterial pathogens are important in BRDC. Bacterial organisms are responsible for severe pulmonary and other involvement and are often the immediate cause of death. Most bacterial pathogens do not invade and cause pneumonia and other symptoms unless preceded by stress and/or viral infection. Major bacterial pathogens include:

1. Pasteurella haemolytica. This organism is a common cause of fibrinous pneumonia and is a major target of antibiotic therapy in many episodes of bovine respiratory disease. It is often the first bacterial organism to invade the lung after viral infections have become established.

2. Pasteurella multocida invades and causes pneumonia and other lesions after infection with viral agents and P. haemolytica has become established.

3. Haemophilus somnus causes pneumonia, infection of the central nervous system and other organs.

4. Several bacterial organisms invade after infection with Pasteurella sp. Some of these, especially Corynebacterium pyogenes, are notorious for forming abscesses in the lung and adjacent tissues.

Accurate diagnosis is critical. Bovine respiratory disease complex is usually not caused by a single infectious organism, but a complex interaction of several infectious agents working in consort with the environment and stress. Early professional diagnosis, including submission of specimens to the diagnostic laboratory, is critical. Antibiotic and other therapeutic agents should be selected on the basis of symptoms shown and accurate diagnosis. Sometimes bacterial organisms may be resistant to an antibiotic that has worked well in the past. However, injudicious changing of antibiotics is unwise. Changes should be made carefully in consort with professional diagnostic efforts and evaluation of the efficacy of therapeutic agents. If morbidity (percent sick) is increasing rapidly or therapeutic effect is less than desired, consideration should be given to mass treatment of the entire pen to prevent new cases from occurring and to avoid missing sick animals that do not show obvious symptoms.

A hospital pen should be provided so sick animals can be closely observed and easily treated. In most cases, sick cattle should be held in the sick pen for at least one full day after recovery appears to be complete. A variety of feedstuffs should be made available in the sick pen. The treatment facility should be provided with a floor drain and, if possible, hot running water, so the area can be thoroughly cleaned. In many smaller feedlots, the treatment facility also serves as the processing facility, so provisions for adequate cleaning and disinfection should be made. Sick cattle should not be housed where contact with incoming cattle is possible. They should not have a common indoor air space.

Proper administration of veterinary drugs and accurate record keeping is essential for quality assurance programs.

For cattle of unknown origin or that have not been pre-conditioned, it is almost always advisable to vaccinate and treat for parasites on arrival. In most cases, re-vaccination is advisable. Cattle can sometimes be rested for 24 hours, but it is rarely advisable to wait longer. Processing programs usually include the following:

1. Vaccination for IBR, BVD, PI-3, and BRSV, 7-way Clostridia and Haemophilus.

2. Treatment for internal and external parasites.

3. Implanted with a growth promotant.

4. Optional vaccinations may include Pasteurella sp.

Carcass condemnation, trimming of lesions, abscesses, adhesions and systemic effects of infection, potential for drug residues and injection site lesions are all important beef quality issues that result from respiratory disease. The most effective way to reduce these BQA risks is to minimize respiratory disese morbidity. Other key points are:

1. Injection technique. Use only needles at least 1-inch long. Make sure they are sharp, and discard them when they become dull, bent or damaged. No injections should be made posterior to the shoulder blade. No injection should ever be made into the hip or rear leg. Follow label directions when using pharmaceuticals or vaccines. Use subcutaneous products when available. Never inject more than 10 ml (cc) of an antibiotic at one site.

2. Injection equipment. Syringes, needles and other injection equipment should be heat sterilized. Any disinfectants, including alcohol, if used, must be thoroughly rinsed from equipment or they will neutralize vaccines and chemically react with some antibiotics. If disinfectants are used, syringes should be thoroughly rinsed with sterile water before use.

3. Drug residue avoidance. Observe label directions and withdrawal times carefully. If dosages are increased, withdrawal times are significantly increased as well. When using exra-label drugs, work closely with the veterinarian on dosages and withdrawal times. Never use an unapproved veterinary drug in an extra-label manner without consulting with the feedlot veterinarian. Doing this without direction by a licensed veterinarian is an illegal act. Some drugs (chloramphenicol, diethylstilbestrol, clenbuterol, and several others) are illegal drugs and cannot be used in food animals.

4. Drug and vaccine storage. Purchase fresh vaccines and store them in a refrigerator. Veterinary drugs should be stored in a cool, dry area. Most should be refrigerated. Never use an outdated drug. Probably the most dangerous violation of BQA principles is to store veterinary drugs in the feed or feed-additive room. This is especially true for pesticides. Catastrophic episodes occur every year, because a drug or presticide is stored in the feed room and accidentially incorporated into the feedlot ration.

5. Records. Careful records should be kept of all treatments and vaccinations. These records should include the date, product used, dosage, route of administration, injection area (left neck, right neck, etc.) and withdrawal date. These records are useful when analyzing disease control and BQA strategies.

Reference:
1 Faber, et al. The Costs and Predictive Factors of Bovine Respiratory Disease in Standardized Steer Tests. Beef Research Report, Iowa State University, 90-100. 1999.