WHEN HIVES APPEAR
Hives, the common term for urticaria, are soft, raised, steep-walled, flat-topped swellings in the skin caused by the accumulation of excess fluid. The horse will most likely have multiple swellings in specific areas of his body, or in some cases the hives may cover the entire body.
So long as the facial and neck swellings do not interfere with breathing, hives are not dangerous, and they usually subside on their own. However hives are a warning: They are a sign that the horse was exposed to something that stimulated an allergic reaction. You will need to figure out what caused it, because if the horse is exposed again, the next reaction could be more serious.
This type of reaction can be caused by external factors, such as insect bites or stings, topical medications or other products, contact with pollens or plants such as stinging nettles, or exposure to other chemicals in the environment. Internal or ingested allergens can also cause hives; some horses may be allergic to certain foods or feed additives, for example, as well as some ingredients in medications or vaccines.
Sometimes, the trigger of a horse’s hives will be obvious. “It’s an immediate reaction, so you know it’s something the horse came into contact with quite recently,” says Rosanna Marsella, DVM, DACVD, of the University of Florida in Gainesville. “If you know when the hives started you can think back 20 or 30 minutes to realize when the insult happened.”
If the hives appeared soon after the use of a new shampoo, for example, simply changing to a product with different ingredients will most likely take care of the problem. If the hives appear after a horse receives a dose of medication or a vaccine, you’ll want to alert your veterinarian, who may prescribe a different drug or a vaccine with a different formula.
In some cases, it may take a little more sleuthing to discover what has triggered a case of hives. “Sometimes when the horse is out on pasture the hives might not be noticed right away, so you aren’t sure what caused them,” says Marsella.
Consult your veterinarian if a horse develops hives repeatedly and you can’t figure out why. You may need to do allergy testing to identify which element in a horse’s environment is causing the trouble. “If the horse’s allergies get worse—which is typical, over time—you have to do something about it,” Marsella adds.