Bovine respiratory disease
The complex of viral and bacterial causes for bovine respiratory disease (BRD) or illness commonly known as “shipping fever” does not respect age or condition of cattle and will become opportunistic whenever the advantage may arise. Outbreaks of disease can occur sporadically and without warning, causing a high incidence of disease within the herd, particularly new arrivals and young animals. Producers suffer financially due to decreased weight gain and feed efficiency. Fortunately, ill animals can typically respond well to therapy when instituted early in the course of the disease.
Commonly detected bacterial pathogens are:
Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. Viruses such as bovine respiratory syncytial virus, infectious bovine rhinotracheitis, bovine viral diarrhea, and ParaInfluenza virus have also been implicated in pneumonia cases.
Many of these viruses and bacteria will only cause mild symptoms when presented alone, but together will ultimately cause more severe disease in the animal. Respiratory disease is the leading cause of calf deaths from three weeks of age and older, according to data from the U.S. Meat Animal Research Center.
Illness takes off in immuno-compromised animals, especially those entering a new living arrangement and in between transit. Factors such as age of animals, weather conditions, air circulation, injury, dehydration, and other stressors will often influence whether an animal becomes sick. Approximately 120 days of age tends to be the timeframe when outbreak of respiratory illness affects young cattle. At this time, colostrum antibodies are tapering down and calves
that have not begun a vaccination routine are lacking immunity.
Symptoms of illness tend to occur within four weeks from weaning time. Early illness may demonstrate clinical signs of depression, sunken eyes, in appetence, and fever. Animals more severely affected later in the course of disease will have drooped ears, nasal discharge, cough, and present with difficulty breathing where some animals often act as if they are panting heavily or choking.
Interestingly, incidence of disease tends to be higher in males, calves from first time heifers, and dependent upon whether calves were delivered by Caesarean section or those that went through dystocia. Risk factors that almost exclusively relate to disease outbreak are larger herd sizes, introduction of new cattle from several sources, and managing cattle in highly concentrated confinement.
Animals are treated with antibiotics targeted for microorganisms in the lungs and throughout the respiratory tract. Anti-inflammatory drugs are also utilized as an aid to relieving fever. Dehydration may be addressed with oral or parenteral (intravenous or subcutaneous) administration of fluids and electrolytes.
Gathering information regarding disease outbreaks and discussing therapy with veterinarians and other herd managers is an important measure to prevent future illness. Identifying location of origin for affected animals and ages of those that were treated can help mitigate the decision making process for attaining new animals and resources available. Early detection of disease followed by supportive care is crucial to therapeutic success. All new animals to a herd should be adequately quarantined for a reasonable standard of time; 15-30 days if possible.
Vaccines are available in order to prevent onset of disease, severe lung lesions, and illness. Calves initially vaccinated under the age of six months should receive one to two booster doses of vaccines; full immunity does not set in until 10-14 days after a booster vaccine dose is given. Intranasal vaccines are critical to administer during an outbreak of disease, as their onset of action is within three days.
Diagnostic testing and post mortem examinations should be conducted on any animals (especially calves) that die from respiratory disease. Blood and lung tissue samples are most often submitted by your veterinarian to a reference laboratory for analysis.
Consult with your herd veterinarian for further tips on prevention of the economically important bovine respiratory disease. — Dr. Genevieve Grammer
[Dr. Genevieve Grammer is a mixed-species veterinarian practicing in eastern Colorado. Please direct correspondence to drgigi19@ gmail.com]