Bovine Respiratory Disease (BRD)

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Bovine Respiratory Disease (BRD)

Also known as

“Shipping fever”, pneumonia

Description

BRD is the most common and costly disease affecting the North American beef cattle industry. In the broadest sense, BRD refers to any disease of the upper or lower respiratory tracts. BRD in cattle is commonly associated with infections of the lungs, often causing pneumonia in calves that have recently been weaned or recently arrived at the feedlot (which is why it is often referred to as shipping fever). BRD or shipping fever is most prevalent within the first weeks of arrival at the feedlot, but can occur later in the feeding period and is also seen in calves on pasture.

Respiratory tract infections in cattle may be minor (like a cold in humans) or life threatening, depending on the pathogens involved and the affect they have on the respiratory system. Respiratory disease is one of the major illnesses in cattle and can create serious economic losses--due to costs of treatment, lost production (poor weight gain, drop in milk flow), and deaths.

When an animal gets sick, sometimes it’s hard to know what kind of infection it is, since different infectious diseases can cause similar symptoms, and multiple pathogens (such as combinations of bacteria and viruses) may be involved.
    
Many infections are lumped together and called bovine respiratory disease (BRD) since various viruses and bacteria may act alone or together. In many instances viruses are the triggering agents, damaging the surfaces of air passages and giving ever-present bacteria an opportunity to invade. Other irritants that may open the way for infection include dust, smoke, irritating chemicals, ammonia fumes, etc.  

Cattle of all ages are susceptible to respiratory infections--especially young calves with inadequate immunity, or animals under stress. Some of the most serious outbreaks of infectious respiratory diseases occur when cattle from different origins are mixed and stressed, as when weaned, sent to a sale barn and then to a feedlot.

Many bacteria are always present in the environment and considered normal inhabitants of the respiratory tract. Viruses, by contrast, are generally passed from one animal to another by direct contact or via airborne droplets (coughing). Blood samples are often helpful in diagnosis. A veterinarian can also tell, by examining the sick animal, whether the infection involves only the upper respiratory tract or both the upper and lower tracts (lungs). Infection if the lungs is called pneumonia.

Upper respiratory infections are usually mild and not life threatening--unless they weaken the animal’s immune defenses and create ideal conditions for pneumonia. Upper respiratory tract infections by themselves are usually temporary and involve inflammation of the nostrils, throat (pharynx) and/or windpipe. The affected animal may have a snotty nose or nasal discharge, for instance, and no other signs.

If infection involves the throat and/or windpipe, the animal may cough (due to irritation and inflammation in the airways) and may have nasal discharge (clear and runny or thick and snotty) or mild fever and decreased appetite. The animal may be dull for a few days, have a mild fever, and then get better, with or without treatment.

Some infections are caused by viruses rather than bacteria and if any treatment is given, usually all that’s needed is an injection of long-acting antibiotic to make sure no secondary bacterial infection becomes established.

Some animals have one or both ears drooping down and seem dull, but continue to eat and drink. They may recover without treatment, but the animal should be closely watched to make sure it does not get worse--which would indicate secondary infection and pneumonia, and a need for antibiotics. The animal with pneumonia will have a higher fever and usually be off by itself and very dull.

Body temperature is often used to determine whether or not the animal should be treated. Many feedlots routinely treat any animals with fever. Cattle with pneumonia may have a fever of 104 to 108 degrees F.  As a general rule, fever up to 104 is indicative of bacterial pneumonia (but not always), whereas fever of 106 or higher is often due to a virus. A fever of 106 to 107 may mean the animal is infected with BRSV (bovine respiratory syncytial virus.  

An animal with pneumonia quits eating, is dull and depressed and may spend a lot of time lying down. If standing, the animal may be humped up. Respiration may be fast or labored, with grunting sounds as the animal tries to force air back out of impaired lungs. The nose may be snotty or crusted. Nasal and eye discharges may be clear or thick.

If the animal moves, it moves slowly because of pain. In severe cases, breathing is difficult; the animal may breathe with mouth open. In the last stages of pneumonia, before the animal is too weak to stand, it may stay on its feet rather than lie down, since the lungs are so impaired; it’s easier to breathe standing up than when lying down.

Even mild cases of pneumonia early in life may impair the lungs, resulting in less functional lung tissue. Calves ill as babies may not grow well. Sub-clinical pneumonia (so mild you don’t notice signs) may affect growth and future health. These are calves you didn’t realize were sick, or were just a little dull and off feed temporarily and you didn’t treat them. At slaughter, some of these animals have adhesions in the lungs, or 10 to 15% of their lung tissue may be dead.

Signs

  • Fever
  • Cough
  • Nasal discharge
  • Rapid respiration
  • Difficult breathing
  • Dullness
  • Droopy ears
  • Depressed appetite

Cause

BRD is a multi-factorial syndrome that is dependent on a number of different causes. It commonly occurs when the causative organism becomes established by secondary infection, following a primary bacterial or viral infection, which may occur after stress--from weather, handling, transport etc. Usually all of these factors must be present, to cause BRD. Viral pathogens are often present in the herd, with almost no signs, and only cause severe disease when complicated with bacterial infection. BRD often develops within 2 to 4 weeks of transport.

The bacterial agents most commonly linked with BRD are Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. Viral agents include Bovine viral diarrhea (BVD), herpes virus such as Infectious Bovine Rhinotracheitis (IBR), bovine respiratory syncytial virus (BRSV), and parainfluenza type-3 virus (PI-3) and bovine coronavirus. Some parasites such as lungworms may also predispose an animal to BRD.

Host factors (characteristics of an animal that make it more prone to BRD) include age, immune status, prior exposure to the pathogens, genetics, etc. Pneumonia can hit cattle at any age, but is most common (and often most deadly) in calves.

Environmental factors that increase risk include transport, commingling, weather/temperature fluctuation, crowding, dusty pens, poor ventilation in barns, etc. Dirty bedding saturated with urine and manure creates ammonia fumes that irritate the lungs and open the way for opportunistic pathogens.

Infection in the lungs (pneumonia) is often due to downward progression of infection from the upper tract (throat, windpipe, bronchial tubes) or failure of mechanisms meant to protect the lungs. Viruses may damage the lining of the windpipe, allowing infection to get started.

Other factors can damage the lining severely enough to invite infection--such as irritation from smoke or dust. More rarely, lung infection is due to systemic infection brought to the lungs via the bloodstream. Pneumonia is usually much more serious than an upper respiratory tract infection and more apt to be life threatening.

Another illness (such as scours), nutritional deficiencies, etc. can lower the body’s immune defenses. Most pathogens that cause pneumonia are present in the environment; many normal cattle carry one or more bacterial pathogens in their upper respiratory tract without getting sick. These pathogens may get down into the lungs but are usually expelled or inactivated by the animal’s immune system. Some viral pathogens by themselves produce mild signs of illness, but cause severe (and sometimes fatal) disease when combined with other viral or bacterial pathogens and stress.

Viruses tend to reduce the resistance of mucous membranes and can also destroy the tiny hair-like cilia in the bronchial tubes that help keep the lower airways free of harmful pathogens. Damage by viral infection thus makes the respiratory system more vulnerable. 

The windpipe is lined with cilia, which are in constant motion--moving like waves on the ocean in an upward sweep. They move debris and bacteria up out of the windpipe into the back of the throat, to be removed from the body by coughing. But when the cilia are damaged by viruses they can no longer defend the lungs.

Bacterial pneumonia is more apt to kill the calf than a viral infection, but usually there’s a virus there first, suppressing the immune system and damaging the airway lining. In some instances, however, BRSV (Bovine Respiratory Syncytial Virus) can cause enough problems (without any bacteria involved) to create serious lung damage or even kill the animal.      

Some cases of acute viral pneumonia can be fatal in a few hours, but many cases of uncomplicated viral pneumonia recover in 4 to 7 days--unless bacteria become involved. If that happens, the animal may develop toxemia; toxins from bacteria get into the blood and travel throughout the body, making the animal even sicker.

Cattle of any age may develop pneumonia if weather conditions are stressful. Extremes of temperature in fall or spring with hot days and cold nights are especially dangerous; this is why most pneumonia cases occur in spring or fall. Stress-related pneumonia is often due to Pasteurella and may not need a virus to start. When temperature extremes have a differential of 40 to 50 degrees F. or more (80 to 90 degree afternoons, dropping to 40 degrees or less at night, or 60 degree afternoons dropping to 20 degrees or colder at night) there are more Pasteurella pneumonia cases.

In some cases of bacterial pneumonia, endotoxins are produced as bacteria die and their cell walls break up. As toxins circulate through the blood they cause damage in the lungs and adversely affect other organs of the body--creating a life-threatening situation. Heart rate may be weak and rapid, respiratory rate fast and shallow. Normally pink nose and gums are dark due to lack of oxygen in the tissues. Without immediate treatment to reverse this toxic condition, the animal will die.

Prevention

Vaccination can help prevent several types of infection that lead to BRD but are not completely effective in stopping respiratory disease; some of the problems with vaccine effectiveness include improper use, such as failing to time vaccine doses appropriately, or not administering them long enough before weaning or shipping for the cattle to mount adequate immune response.

Vaccines are available for a number of viral/bacterial agents, including IBR, PI3, BVD, BRSV, Pasteurella, and Haemophilus somnus. Many of these vaccines can be given simultaneously, because of their similar dosing schedule. For example, IBR, PI3, BVD, and BRSV vaccines are often sold as combination products.

Some veterinarians recommend vaccinating calves at 4 to 6 months of age with a booster 4 to 6 weeks later, to give adequate protection to weaning age calves. The important thing is to make sure calves are vaccinated twice between 4 and 7 months of age with a product that will help prevent BVD, IBR, PI3 and BRSV.

Calves vaccinated younger than 6 months of age usually need to be vaccinated again at that age, to boost immunity. Follow label directions on vaccines. If 2 doses should be given initially, this means that the animal won’t have much immunity until 7 to 14 days after the second dose is given.

Vaccination should be discussed with your own veterinarian, to develop a program that will be the most effective in your herd. Some vets recommend intranasal vaccines for young calves, on farms that have serious problems. Antibodies from this type of vaccine are not long lasting but may be effective more quickly--to give calves more immediate protection in the face of a herd epidemic.  

No vaccines give 100% protection. They work best in situations where good management minimizes the risks and stresses that predispose animals to respiratory infections.

Calf pneumonia can often be prevented if calves get adequate antibodies in colostrum. This works best if cows have strong immunity during pregnancy (their own vaccinations for viral diseases kept up to date) so they pass high levels of antibodies to newborn calves via colostrum. Make sure each calf gets an adequate amount within 2 hours of birth (while ability to absorb antibodies is greatest).

Calves stressed by a hard birth or chilled after birth may not get up quickly enough to nurse, or may be unable to absorb enough antibodies. Stress hastens closing of the porous intestinal lining that allows passage of antibodies through it and into the bloodstream.

Calves from first-time mamas may not get as many antibodies as calves from older cows; the older cow has come in contact with more pathogens during her lifetime and has more chance to develop strong immunity--which she passes to her calf via colostrum.

Young calves are most susceptible to pneumonia between 2 and 10 weeks of age, when their temporary immunity from maternal antibodies from colostrum wanes--and they have not yet developed their own immunity--but stress can hinder immunities at any age.

Protection from colostrum antibodies is waning by the time most calves are 3 to 4 weeks old, and many cows don’t have strong immunity to Pasteurella, to pass on to their calves. If you have spring and summer pneumonia in calves, talk to your veterinarian about vaccinating calves at a month of age, for Pasteurella.

Make sure there are no underlying herd health problems. Cows may need higher nutrition levels to produce strong colostrum. If calves are getting pneumonia, check the energy, protein and mineral levels in cows’ diet. If a cow does not have a properly functioning immune system (because she’s short on energy, protein, selenium, copper or some other crucial nutrient) or if she’s persistently infected with BVD, her calf won’t have adequate antibodies from colostrum.  

Since stress is the biggest factor in whether cattle develop respiratory disease, try to eliminate or reduce all possible causes of stress--whether nutritional or human caused.  Don’t wean calves or do sorting/vaccinating (or shipping cattle) during bad weather. Avoid mixing different groups of cattle during weaning or processing, and try to control dust and mud. Use low-stress weaning methods.

Treatment            

Cattle don’t have strong lungs; pneumonia can be an uphill battle unless you catch it early. Once the lungs are damaged and filling with fluid, the animal may be hard to save.  It’s important to spot early warning signs. If you can detect that an animal is not feeling well, and diagnose the problem early (by taking temperature) pneumonia is easier to clear up than if you delay treatment until the animal is in serious trouble. Early treatment can help prevent complications such as abscesses in the lungs, inflammation of the lung lining, chronic dilation of the bronchial tubes, or pus-producing infection.

Isolate sick animals to keep them from exposing others if the infection is contagious. To avoid additional stress, a nursing calf should be kept with its mother. If he needs to be under a heater, partition off a corner of the pen or barn stall so he can be kept warm but still have mama nearby.

Antibiotics can help stop bacterial infections. Some antibiotics like Micotil, Nuflor, and Baytril 100 are long-acting and don’t need daily dosing, but Naxcel, Excenel, and Adspec may also be effective as well—to help prevent or combat bacterial infection. Excede and Draxxin are more effective for treating severe bacterial infections than the penicillins or oxytetracyclines and sulfas.

Some stockmen still use oxytetracyclines or a combination of these drugs with sulfa, and in many instances these still work. But sulfa should never be given to a dehydrated animal or it may damage the kidneys. Sulfa is broken down and eliminated through the kidneys and there must be adequate fluid in the body or the sulfa will crystallize in urine and cause irreversible kidney damage--which will be fatal.  

When dealing with a stubborn pneumonia that’s not responding to the drugs your veterinarian prescribed, don’t wait too long before asking about changing antibiotics. If no improvement is seen within 48 hours, you should change to something else.  

Always read and follow label directions (or your veterinarian’s advice--since in some circumstances he/she may prescribe a different dose or schedule) for dosage and timing.  Some drugs must be given daily; others can be repeated every 48 hours, and others every 3 days.  Make sure you are using them properly.

Many vets don’t recommend Nuflor in calves younger than 30 days because it can be hard on the digestive tract and cause scouring. Micotil (tilmicosin) has safety precautions (fatal if injected into a human).  Baytril and A180 are similar in effectiveness but A180 has the advantage of being less expensive, with shorter withdrawal time before slaughter, and it concentrates in lung tissue a little better.

Draxxin has an advantage in needing fewer treatments. It concentrates in the lung and stays there about 8 to 10 days. Thus you can give one shot and may only need to handle the animal once.

Excede is also good for treating respiratory infections and is approved for use against Pasteurella and Haemophilus somnus (both are often involved in pneumonia and shipping fever) and is injected under the skin on the back middle third of the ear.

Sustained release formulation provides adequate blood levels for 7 to 8 days with a single injection. Your veterinarian must show you how to give this injection; giving it improperly can result in immediate death of the animal.

Regardless of which antibiotic you use, key to successful treatment is catching BRD quickly, though this can be difficult. Often by the time the animal is obviously sick, there’s lung damage. Studies have shown that damage from Pasteurella can become permanent within less than 8 hours. By that point there’s scarring in the lungs even if your treatment clears up the infection.

Once abscesses form in the lungs, or there’s too much damage and scarring, antibiotics may not be helpful and you might not save the calf—and once permanent damage exceeds 20 to 25% of the lung tissue, the animal may do poorly even if it survives.

Calves that suffer permanent lung damage may not grow well, and may die about the time you plan to send them to market--when they outgrow their lung capacity.  

Antibiotics should always be given, even if pneumonia is caused by a virus, since secondary bacterial infection could kill the calf. Be diligent with treatment, and don’t stop too soon.

Even if the animal is breathing easier and feeling better (eating and drinking again, with temperature back to normal), keep antibiotic levels high for at least 2 full days after all signs are gone. If the animal relapses, it will be harder to save it the second time around.

Secondary bacterial pneumonia will usually respond to antibiotic treatment, but relapses are common if viral infection is extensive, and by that time it may be difficult to save the calf even if you start treating him again.

Supportive care is also important. Make sure the animal is warm and dry, protected from bad weather. If it is not eating or drinking, force-feed fluids and nutrients. A calf can be fed milk or milk replacer via stomach tube.

An esophageal feeder works well for young calves; a larger calf or adult animal cam be fed fluid and nutrients via nasogastric tube (into the nostril) since the esophageal probe is not long enough.

Anti-inflammatory drugs should be given to halt the cascading effect of prostaglandins that will destroy the lungs, and to help reduce fever, pain and inflammation, and block the effects of endotoxins.

It’s usually wise to use a non-steroidal anti-inflammatory that can reduce inflammation and halt prostaglandins without suppressing the immune system (as steroids do), but at the very beginning of the inflammatory process you can head it off best with dexamethasone.

After that, you can help shut it down with Banamine. Anti-inflammatory medication works well to minimize lung damage in animals and can also help the animal feel better--and resume eating and drinking.  

Banamine reduces fever, cough, respiratory rate, discomfort, and lung congestion. Animals with pneumonia often recover faster if given Banamine than when given antibiotics alone, but don’t give Banamine to a dehydrated animal or there’s risk for kidney damage.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.

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