I own a nine-year-old Thoroughbred gelding that weighs about 950 lb (430 kg). He is worked five days a week with the goal of competing in low-level eventing. He is allowed about six hours on pasture each day; the rest of the time he is kept in a stall. In addition to the pasture, he is fed about 3 lb (1.3 kg) of a senior feed, beet pulp, salt, probiotics, and a biotin supplement each day. It is difficult to maintain his weight, and he is hot-tempered to ride. Further, he seems to have endless stamina, so my riding sessions can be long and strenuous for both him and me. Can you help me determine if his diet is creating excessive energy?
You can influence behavior with diet to some extent, depending very much on the individual horse. For example, one of our research horses, also a Thoroughbred, is very sensitive to the type of feed he consumes, while others in our herd are not as obviously influenced. This horse is much calmer when fed a high-fat, high-fiber feed (low in nonstructural carbohydrates [NSC]) than when fed a high-starch feed.
You are not feeding a high-NSC diet, but some subtle dietary changes may help. Consider switching out your current senior feed and beet pulp for a low-NSC feed. While beet pulp is a highly digestible fiber, it can have enough residual sugar to the horse’s glycemic response, especially if it contains molasses. One such alternative is Re-Leve, a feed very low in starch and sugar but high in digestible fiber and fat. The added fat could be especially advantageous in this case because weight management is an issue. Fat is often referred to as “calm energy” because adds significant calories but does not have the same effect on making a horse more excitable as a starch and sugar can do with some horses. Aside from feeding a high-fat feed, you can gradually add some vegetable oil to the diet, which would increase the calories from fat.
You did not mention what type of forage your gelding consumes, but if you are feeding alfalfa you may consider changing to grass hay. Alfalfa has often been thought to have a revving effect on the temperament if a horse has a predisposition to being hot. There are more calories in alfalfa than grass hay, which is why alfalfa is helpful for putting and maintaining weight on a horse. Therefore, if switching to grass hay from alfalfa, a greater quantity of hay will probably need to be fed to supply the same number of calories.
Sometimes the behavior we see with horses when they are under saddle is influenced by other aspects of management. In the early days of horse racing, the British figured out that if a racehorse was penned up all day it would run harder. From that came the tradition of stalling certain performance horses. Often a horse may be hot or playful under saddle because he has lots of pent-up energy from being kept in a stall too many hours in the day. I realize it may be difficult in your situation, but if there was any way to manage this horse with 24-hour turnout, you may have a different animal to ride. If you could at least allow him more hours turned out than stalled, it would be a start.