Enzootic pneumonia of calves is the most common respiratory disease seen in young dairy, veal, or beef calves. The disease is caused by a variety of viral and bacterial pathogens and environmental risk factors (poor ventilation, high humidity, crowding, poor transfer of passive immunity, mixing of age groups) predispose calves to disease. Treatment consists of broad-spectrum antimicrobials effective against the most common pathogens.
Estimates suggest that 30% of dairy calf deaths can be attributed to enzootic pneumonia of calves. Morbidity rates for individual groups of calves can reach 100%; case fatality rates vary but range from 5%–20%. Early identification of cases can be improved with the use of standardized scoring systems.
Etiology of Enzootic Pneumonia of Calves
The etiopathogenesis of enzootic pneumonia of calves involves environmental and management stressors, possibly an initial respiratory viral infection, and secondary bacterial infection of the lower respiratory tract. Important risk factors include:
inadequate transfer of passive immunity
waning passive immunity at 2–4 months old
inadequate ventilation
high-humidity environments
rapid weather changes
crowding of calves (in beef calves on pasture this may occur during other management procedures, such as estrus synchronization)
mixing of age groups
poor nutrition
Any of several viruses may be involved, and a variety of bacteria may be isolated from affected calves. Mycoplasmal and bacterial agents, including Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, and Mycoplasma bovis, represent the most frequently isolated pathogenic bacterial organisms. The individual viral and bacterial etiologies, clinical signs, lesions, and treatment are discussed under Viral Infections Associated with Bovine Respiratory Disease Complex in Cattle Viral Infections Associated with Bovine Respiratory Disease Complex in Cattle Bovine herpesvirus 1 infections are widespread in the cattle population. In feedlot cattle, the respiratory form is most common. The viral infection alone is not life-threatening but predisposes... read more 
and Bacterial Pneumonia in Cattle with Bovine Respiratory Disease Complex Bacterial Pneumonia in Cattle with Bovine Respiratory Disease Complex Mannheimia haemolytica serotype 1 is the bacterial pathogen most frequently isolated from the lungs of recently weaned feedlot cattle with bovine respiratory disease (BRD) and in dairy... read more 
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Diagnosis of Enzootic Pneumonia of Calves
Thoracic Ultrasonography
Portable ultrasound machines typically employed by food animal veterinarians for reproductive examinations have proven to be a useful noninvasive tool in the diagnosis of bovine respiratory diseases including enzootic pneumonia of calves. Training in interpretation of ultrasound findings, a systematic approach to examination, and a standardized categorical scoring system (from 0-5) are key to using this diagnostic technique.
Thoracic ultrasonography can identify calf populations:
at risk for developing BRD
to monitor the prevalence of BRD in groups of calves
to assess disease severity and estimate prognosis in individual animals
The sensitivity of ultrasonography in diagnosing pneumonia has been estimated at 80%–94%, and the specificity has been estimated at approximately 94%–100%. Cellular infiltrates and lung consolidation appear as hyperechoic comet-tails or mottled patterns deep to the hyperechoic pleural surface. Severity of disease identified on ultrasonography has been reported to correlate with lesions found at necropsy. 1 For More Information Enzootic pneumonia of calves is the most common respiratory disease seen in young dairy, veal, or beef calves. The disease is caused by a variety of viral and bacterial pathogens and environmental... read more
Culture and Sensitivity Testing
Evaluation of pathogen profiles involved in calf pneumonia is another important element of diagnosis. In individual animals, bronchoalveolar lavage is the preferred method of sampling to test for bacterial and viral pathogens. To evaluate herd-level pathogens, deep nasopharyngeal swabs are recommended when sampling multiple calves. In both situations, early cases of respiratory disease should be sampled prior to treatment.
For More Information
Ollivett TL, Buczinski S. On-Farm Use of Ultrasonography for Bovine Respiratory Disease. Vet Clin North Am Food Anim Pract. 2016 Mar;32(1):19-35. doi: 10.1016/j.cvfa.2015.09.001. PMID: 26922110
Control and Prevention of Enzootic Pneumonia of Calves
For control and prevention of enzootic pneumonia of calves:
Ensure optimal intake of high-quality colostrum to ensure good passive transfer of immunity.
Ensure an appropriate vaccination protocol for respiratory pathogens in the cow herd.
Vaccinations for young calves against respiratory pathogens may also be warranted.
Avoid crowding of calves and mixing of age groups.
"All-in/all-out" management styles should be used when calves are assembled into groups.
Calf hutches or well-ventilated calf housing, separate from adult animals, is essential for limiting this disease in housed dairy or veal calves.
Provide adequate nutrition for young calves to avoid protein and energy deficiencies.
Key Points
Control of predisposing risk factors such as ventilation, housing, nutrition, and passive transfer of immunity is essential.
Early identification of cases and identification of pathogens promotes appropriate selection of antimicrobial treatment.
Thoracic ultrasonography allows for herd screening and also assessment of disease severity in individual animals.
Morbidity of enzootic pneumonia is high; weight gain is reduced and overall development of affected animals is delayed.
