About the Disease

Bovine Respiratory Disease: Causes and Signs of Disease

Dr. Dee Griffin, feedlot management specialist at the Great Plains Education Center of the University of Nebraska, authored the report from which this information is taken.

Causative factors

Over the past decade, a number of viruses, bacteria, and other organisms have been associated with acute BRD. Individually, these organisms – or pathogens – do not appear to be capable of causing disease in healthy cattle. But interaction among pathogens commonly occurs in conjunction with various stressors, which seems to be critical to the development of BRD.

  • VIRUSES. Bovine herpesvirus 1 (BHV-1, or IBR), parainfluenza 3 virus (PI3), bovine viral diarrhea virus (BVDV), and bovine respiratory syncytial virus (BRSV) are the only viruses that can cause acute respiratory disease without significant interaction with other pathogens.
  • BHV-1 is associated with several diseases, but it is most often considered a respiratory pathogen.
  • PI3 is generally a severe respiratory pathogen in young cattle only, although cases of severe PI3 infection have been reported in yearling cattle.
  • BRSV is a severe respiratory pathogen in newly weaned cattle. BRSV outbreaks in yearling cattle are rare but have been reported.
  • BVDV is not considered to be a primary respiratory pathogen. This virus, however, suppresses the immune system, which allows other organisms to more easily establish an infection.
  • BACTERIA. In general, bacteria do not serve as primary pathogens of BRD in healthy, unstressed cattle. The bacteria and bacteria-like organisms that have been most commonly associated with the BRD disease process include:
    • Mannheimia haemolytica
    • Pasteurella multocida
    • Histophilus somni
    • Mycoplasma spp.
    • Chlamydia spp.

M. haemolytica is more commonly isolated in fatal cases of BRD in younger cattle than in yearling cattle. M. haemolytica type A1 causes the most severe damage of all the recognized bacterial pathogens.

P. multocida is believed to cause less acute respiratory disease but is reported more often than M. haemolytica. Its frequency of isolation from fatal cases of BRD in cattle less than 7 months old makes it a primary concern in many operations. Along with two other less significant bacteria, P. multocida is consistently isolated from abscesses in the throats of Southern Plains cattle suffering from the “hard breather” syndrome.

H. somni is reported more often in fatal cases of BRD in Canada than in the High Plains and Midwest regions of the United States. Differences in livestock genetics and production practices among regions may account for this discrepancy.

Mycoplasma and Chlamydia spp. are commonly isolated by some diagnostic laboratories, but neither is considered a primary pathogen in weaned or yearling cattle.

Stressors

Environmental, nutritional, and management stressors are not primary causes of BRD. Rather, stress causes a rise in blood levels of glucocorticoids, substances which suppress the immune system. As with BVDV, this situation allows pathogens to more easily establish an infection.

Environmental stressors include heat, cold (particularly when wind, rain, or mud are involved), dust, and toxic fumes.

Nutritional stressors include ration changes, irregular feeding schedules, inadequate access to clean water, and perhaps a need for micronutrient supplementation.

Management stressors are numerous. Weaning, transport, commingling, crowding, and processing are some of the most common.

Interactions

Damage to the respiratory tract caused by respiratory viruses disarms the animal’s innate defense mechanisms. As a result, bacteria that are present in the respiratory tract are allowed to grow and establish an infection. (A cut or scrape, for example, is more likely than intact skin to become infected.) Then, if the animal is stressed, its ability to overcome the infection is weakened, and the BRD process begins.

Signs of disease

Observable – or clinical – signs of BRD usually develop 5 to 14 days following environmental or management stresses. Variations in the clinical signs of BRD are associated with the many causative factors involved in the disease process. Signs include:

  • Lack of appetite
  • Runny eyes
  • Loose feces
  • Rapid breathing
  • Soft coughing

The onset can be very dramatic, with some cattle found dead and a large percentage in a group showing severe depression. Treatment early in the disease process is important.

In experimentally induced BRD, the most common and perhaps most important early sign is decreased appetite. This decrease has been shown to occur 24 to 48 hours before an increase in body temperature.

Decreased feed intake in a group of cattle can signal the need for closer observation of individual animals. Changes in individual cattle feed intake can be evaluated by carefully observing the shape of the animal’s abdomen. A slight abdominal bounce can often be observed in sick cattle. Cattle that have been anorexic for more than 24 hours exhibit an abdominal tuck or slab-sided appearance.

Diarrhea is more common than firm stools in cattle suffering from BRD.

The respiratory rate in cattle can be very difficult to evaluate. Fermentation in the rumen can alter the respiratory rate, and for that reason, it is much more difficult to evaluate cattle in the afternoon. Cattle that develop BRD late in the feeding period typically develop severe shortness of breath. Many have an elevated head, excessive salivation, and labored breathing. Their attitude is anxious and belligerent because of their severe lack of oxygen.

In the early stages of BRD, a slight, generalized depression can be noticed. Cattle hold their head slightly lower than normal or, if they are suffering from an emphysema-like condition, they typically elevate their head. Their attitude is a bit distant, and they are less interested in what is occurring in their environment. They do not groom their hair as vigorously as normal cattle do, and they may appear to be trying to hide behind other cattle, between cattle at the feed bunk, or in the corner of the pen. To notice slight changes in depression, it is important to move all cattle and get a good look at each animal.

The cough associated with BRD is usually soft and repetitive.

Early in the disease, cattle suffering from BRD often have watery, dull eyes and a clear nasal discharge. They may rapidly lick their nostrils yet have a relatively dirty nose. Membranes around the eyes and inside the nostrils often appear reddened.

Cattle with BRD often have slightly stiffer movements than normal and exhibit a shortened stride. Affected animals may drag their toes or knuckle slightly. Their tail may appear to be tucked slightly between their hocks.

The temperature of cattle suffering from BRD ranges from 103° to 108°F. Variation in individual animals is influenced by the stage of disease, outdoor temperature, design of the examination/treatment facilities, temperament of the animal, and the animal handling ability of the doctoring crew. High body temperatures in cattle that appear relatively bright and alert are most often observed in the early stages of disease. High body temperature in severely depressed animals is a serious sign.