What can you tell me about hives on horses. The welts or wheals that you have noticed on your horse are indeed indicative of the skin condition known as hives. The condition's proper name is urticaria, and it is characterized by these bumps, which are really localized edemas or swellings in multiple sites. The swellings result when the capillaries beneath the skin leak a clear fluid from the blood into the tissue spaces below the skin's surface. This condition in horses is similar to hives in humans.
Most cases are allergic in origin, and there are many different causes of the allergic reaction.
Hives can be caused by reactions to drugs, especially to antibiotics and nonsteroidal anti-inflammatory drugs. Other causes include allergies to food, reactions to topical drugs or ointments placed on the skin, and seasonal reactions to pollen and molds in the environment. Occasionally hives are secondary to digestive disturbances. The welts that you have noticed occur most often on the neck and shoulder, but occasionally they can be found all over the body, including the legs. Most cases of hives are mild, but it is possible to develop a more acute case and the swellings can converge, forming a larger area.