The thyroid gland secretes hormones that are essential to keeping a horse healthy, including the hormone thyroxin. A thyroid that is not secreting enough thyroxin is said to be sluggish. A sluggish thyroid is also called "hypothyroidism" or "goiter." It occurs mostly in foals but can strike a horse at almost any age. An overactive thyroid can cause a condition known as "hyperthyroidism." With the proper diagnosis and care, horses with either of these conditions can survive. Read on for some of the common symptoms of thyroid problems in horses.
It's easy to see the symptoms of goiter in a foal, because the thyroid gland in the neck will be grossly enlarged, forming a lump. The foal will also be very weak and will need to be bottle-fed. Goiter in foals is thought to be caused by a genetic problem or a dietary problem with the broodmare. If she has too little or too much iodine in her diet, a foal with a goiter can be the result, although foals with goiters often completely recover.
The signs of hypothyroidism in an adult horse are a little harder to spot. One thing common to many horses with hypothyroidism is obesity. A horse with hypothyroidism may continue to be obese even with more exercise and a noticeable drop in her appetite. These symptoms may also be indications of another illness, so your vet has to give your horse a thyroid test to make an accurate diagnosis.
Because the horse's body will not have the proper amount of thyroxin, he will seem to be tired all the time. This may make him reluctant to work, or he will tire far more easily than usual. He may not even be as interested in food or sex as usual. His reactions will be delayed, and he will take far longer to respond to even the simplest of commands.
The horse may have trouble shedding her winter coat, even if there is a noticeable rise in temperature. In this case, you will need to clip off the coat yourself. She also may not be able to grow a winter coat or it may grow raggedly, when in years past, she did not have any trouble growing a coat. The coat will also feel rough instead of soft. It may even stick up instead of lying sleekly against the skin.
Hyperthyroidism occurs when a horse's thyroid makes too much thyroxin. This usually happens due to nutritional problems or ingesting too much medication to get rid of hypothyroidism. Signs to watch out for are weight loss with appetite increase, extreme excitability and sweating more often. The horse may also have a problem relaxing.