ALyme disease can be a difficult problem to diagnose. Luckily, it appears that horses are intrinsically resistant to the organism, but cases do occur. Horses seem more prone to infection if they are immunocompromised or have other stress factors, such as poor nutrition, poor fitness, or other ongoing health issues.

Diagnosis is based on three factors:

• First, a physical examination will demonstrate an otherwise unexplained lameness, usually involving the larger joints and often shifting from limb to limb. A fever might or might not be present, and generalized stiffness and behavior changes can occur.
• Second, a positive serologic test showing high titers to the organism can indicate the infection is active, but it also can show the horse has been exposed to the organism and now has a level of immunity.
• Third, a positive Western blot test is actually indicative of active flagellae in the bloodstream. In some cases, a skin biopsy or a synovial (joint) membrane biopsy might be indicated to confirm the diagnosis.

From your question, I am assuming that your horse is on oral doxycycline administered twice daily for 30 days. This has traditionally been the treatment of choice. However, there is some current evidence that it might not be as effective as once thought. If the horse is not responding appropriately, intravenous oxytetracycline given twice daily for two to four weeks might be an alternative. I would recommend that the antibiotic regimen be completed with an additional convalescent period of 30 days before you ship your horse. Any added stress can affect the health and recovery of your horse. Any situation where the immune system is compromised can lead to a flare-up of the organism if it is not completely cleared, and immune stimulants have not been shown to help