Pastern dermatitis is a fairly common condition, especially in draft horses and other horses with feathers on their legs. This condition is caused by many factors, including allergies, but one cause is a skin mite that causes inflammation and leads to infection. The mite can be found on many farm animals so other animals can be a source. One treatment thought to be effective was using a dewormer like ivermectin or Quest. To test this theory, Quest was used in a group of horses known to be infected with mites; Quest was chosen because it is in the tissue longer than ivermectin. All horses were treated orally on day zero and again on day 21. The stalls were cleaned and disinfected on day zero and again on day 14. They also used a placebo group that was not treated with Quest but the stalls were cleaned.
Results indicated that the group of horses treated with Quest still had just as many mites on the legs as those not treated at all. So if you have a horse with pastern dermatitis caused by mites on the legs, treating with Quest and ivermectin are unlikely to be helpful. Although owners do not like the horse's feathers clipped, this is critical in most cases to kill the mites by using lime sulfur dip or frontline spray topically on the legs. Most of these horses also need to be on systemic antibiotics as well as topical antibiotics, and topical steroids to reduce the inflammation. Pastern dermatitis is a serious condition that can cause scarring and chronic infection on the legs that can lead to chronic pain and lameness.