Q. I have a 10-year-old mare being treated for pinworms. She incessantly rubs her tail. She also uses the wall of her stall or anything else available to lean on while defecating. Are these signs related? Could they be behavioral?

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A. Part of the diagnostic process should include a thorough veterinary exam to rule out neurological abnormalities, skin problems, or other parasitic diseases. A tail injury or cauda equina syndrome (damage or inflammation to the end of the spinal cord and nerve roots) could potentially manifest into persistent itching and inability to raise the tail for defecation.

If this is a seasonal occurrence, consider some pruritic (itchy) rule-outs such as folliculitis, allergic dermatitis, or insect sensitivity. Some horses respond to topical corticosteroid creams and ointments or oral corticosteroid (azium) granules for allergic disease.

Cases of moist dermatitis can occur any time of the year. This can show up as pruritic flaking, crusting, and oozing areas of redness and varying degrees of hair loss. Moist dermatitis can be treated with a medicated shampoo like tar/sulfur or oatmeal base in addition to topical corticosteroid/antibiotic combination creams and oral therapies like azium and/or antibiotics. Once a neurological cause has been ruled out, instituting ivermectin therapy can treat internal parasites as well as potential atypical infestation with Onchocerca or Habronema parasites in the skin. These parasitic nematodes in the larval stages live in the skin and subcutaneous tissues and can cause severe inflammatory responses. Behavioral causes can be addressed once all the medical rule-outs have been considered.

About the Author

Jim F. McDonald, DVM

Jim F. McDonald, DVM, practices in Camp Verde, Ariz.

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