You have been treating your horse's leg wound for a period of time, hopefully with veterinary guidance. The wound is getting smaller and seeming to heal well. But one day you suddenly notice increased swelling, or sudden onset of lameness. What might this mean?

Normal skin is covered in bacteria. Healing wounds are covered in bacteria. Cleaning a wound temporarily reduces the bacterial population but it does not rid the wound bed of bacteria, and the bacterial population rapidly returns. This is ok, because a normal bacterial population is an expected part of the healing process. Antibiotics change this bacterial population but certainly do not rid the wound of bacteria.

However, sometimes normal bacteria can colonize the deeper part of the wound, and create a closed infection, either under the skin or within the tissues. Since it cannot drain, it swells resulting in an abscess.

Worse yet, during healing, suddenly bacteria might gain access to a tendon sheath or joint. In most cases, swelling and lameness will result.

In other cases, abnormal or "bad" pathogenic bacteria can create a significant wound infection, which causes inflammation, swelling and lameness.