If a foal presents with swollen joints, what is the most likely diagnosis?

In cases where a foal presents with swollen joints, foal septicemia, particularly due to E. coli, is often the most likely diagnosis. Septicemia in foals, especially those under one week old, is a critical condition where bacteria enter the bloodstream and can lead to infections in multiple areas, including the joints. The presence of swollen joints indicates potential joint infection or inflammation caused by the spread of bacteria from the bloodstream to the synovial fluid in the joints.

E. coli is a common pathogen involved in septicemia in foals. The systemic infection can lead to localized infections, manifesting as joint swelling and pain. Other signs may accompany this condition, such as lethargy, fever, or poor nursing behavior, further supporting a diagnosis of septicemia.

While joint luxation can cause swelling, it is less common and would typically present acutely after trauma. Viral arthritis and bacterial pneumonia, though they can occur in foals, are less directly related to joint swelling as a primary symptom. Overall, the combination of the foal’s age and the signs of swollen joints strongly points to foal septicemia as the most probable diagnosis.