21/12/2025
Bovine Respiratory Disease
A client called me to examine a 5 month old weaner steer that was lethargic and not eating. He had a temperature of 40.5C, harsh lung sounds with crackles and a heart murmur. A presumptive diagnosis of bovine respiratory disease (possibly Histophilus somni) was made, with a suspicion of haematogenous spread of bacteria to the heart. The steer was treated with antibiotics and anti-inflammatories but a guarded prognosis for recovery was given. He died 8 days later. On post mortem of the heart an abscess (yellow arrows) was found at the base of the mitral valve (green arrow). The lungs had severe, diffuse interstitial pneumonia. No bacteria could be grown on culture but Histophilus somni was confirmed via a specific PCR test. This case is a good example of why some animals do not recover despite antibiotic treatment. Antibiotics can effectively kill the causative bacteria but they cannot undo the extensive damage already present in organs, often resulting in organ failure.
Bovine respiratory disease complex can involve one or more viral and/or bacterial agents. Risk factors for the development of disease include host vulnerability (poor condition/nutrition, age, concurrent disease, lack of colostrum), management stress (weaning, transport, sale yards, mixing cattle from different sources, stocking rate) and environmental factors (cold/heat stress, sudden changes in temperature, dust).
