Q:My horse has a swollen 24-inch "vein" on the middle of his underbelly and all the way up to his genitals, which are also swollen. Is there any topical application I can apply to reduce the swelling? There also was a hard lump near this where it seemed some type of insect bit him.

Paulette Novak, via e-mail

A:Without seeing and examining this horse, it is hard to determine what is actually going on. I always recommend having your veterinarian examine the horse to determine the underlying cause of the swelling. In my experience this type of swelling can be seen for a variety of reasons such as infection, bites, kicks/wounds, and dirty sheaths and bean formation, among others.

As you surmised, a bug bite can cause local swelling and edema (abnormal fluid accumulation beneath the skin), which is usually transient or short-lived. I have seen animals in which a bite from an insect, spider, or snake can also have major side effects and carry infection (which is why I recommend a veterinary exam). Swelling toward the back half of a male horse’s abdomen and the sheath can also arise due to a dirty sheath with significant smegma buildup or the presence of a bean (a buildup of smegma in the fossa around the urethra of male horses). Beans can become very large and can compress the urethra, making it difficult or painful to urinate, so it is important to check for a bean and clean the sheath and penis at least yearly. This will allow you to determine if this is the cause of the swelling