Insufficient calories: If a horse is not receiving enough calories via a combination of roughage and grain, he will lose weight, especially as his "race-fit" muscling disappears. Over the years at New Vocations, I have found that insufficient feed is the number one cause of weight loss in adopted horses.
Parasite infestation: Horses should be dewormed every 60 to 90 days, and at the track, Thoroughbreds are on a schedule to ensure this. While you should request information regarding the horse's last deworming when you buy or adopt him, it may not be available. As a precaution, it is always good to deworm a new horse to help avoid problems with condition as you begin retraining.
Heat: In a hot climate, or during the very warm seasons, a horse that spends long periods in direct sun will burn more calories than a horse that is in a stall, run-in shelter, or in the shade. If your horse is turned out all the time, it is important to provide him a means of shelter and shade. Inside a barn, fans can be positioned to help cool hot horses.
Cold: In regions that experience extreme cold temperatures, or during bouts of cold weather, a horse that is turned out with no shelter to protect him from wind, snow, and rain, will burn extra calories as he tries to stay warm, especially if he's wet. As in areas that experience severe heat, it is necessary to provide adequate cover from the weather. In addition, horses with thinner winter coats or those in the coldest climates may benefit from a blanket or rug.
Fighting insects: Thoroughbreds hate insects. They tend to be thin-skinned and especially sensitive to biting flies and mosquitoes, so expect the weight to "melt" off your horse if he spends too much time fighting the bugs--inside as well as out. There are a variety of products available, including sprays, wipes, masks, and sheets, that can help keep your horse comfortable. And, scheduling turnout for the least buggy time of day is recommended.
Pacing the fence: Running back and forth along the fence line obviously contributes to weight loss. This can be due to initial anxiety about being turned out, boredom, horses in neighboring paddocks, or a lack of company in one's own. I explain how to avoid or deal with this problem further in Beyond the Track.
Sickness: One indication of illness or disease is weight loss. Illness also weakens the horse's defenses against sudden changes in weather and parasite infestation, which contributes to the problem. If a horse is in poor condition and seems depressed, off his feed, or otherwise unwell, have your veterinarian examine him to rule out an underlying problem.
Teeth: Horses may have difficulty chewing and consequently digesting their food if teeth are sharp or in poor alignment. Watch the horse eat and note if he drops a lot of food out of his mouth while he chews. Other indicators of mouth discomfort can include issues with the bit, head-tossing, or poor behavior. A veterinarian or equine dentist can check your horse's teeth and "float" them--file down sharp and rough edges that may be causing problems.
This article is excerpted from the book Beyond the Track: Retraining the Thoroughbred from Racehorse to Riding Horse, which offers tips on finding the right OTTB and giving him the solid educational foundation he needs to excel in a new career. To order, call 800-952-5813 or visit HorseBooksEtc.com.