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.
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:
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 and Bacterial Pneumonia in Cattle with Bovine Respiratory Disease Complex .