Diagnosis This foal suffers from localized septic arthritis, most likely in the early stages of the disease. In the early stages of septic arthritis, the joint can appear normal with a joint tap. Neutrophils may take a few days to appear. The synovial membrane is often inflammed, with the possibility of physeal bone involvement. This foal doesn't appear to have physeal bone involvement. He does have pitting edema, which is a sign of low-grade inflammation. Possible sources of infection include: failure of passive transfer, pneumonia, umbilical infections, enteritis, and extension of penetrating wounds. In this case, the umbilical infection, or the penetrating wound seem to be the most plausible causes. If he had failure of passive transfer, he would have exhibited signs at an earlier date. If the problem was pneumonia, he would have shown respiratory signs. In the case of enteritis, he would have shown colic, diarrhea, or other gastrointestinal complications. The Klebsiella found in the joint tap supports this diagnosis, because it is one of the most common etiological agents found in septic arthritis.