My 10-year-old Thoroughbred gelding has 24-hour access to a large pasture. In addition to pasture, he gets two pounds (0.9 kilograms) of a fortified feed and hay as necessary. He is a good doer, so maintaining weight is not a problem. I ride him six days a week for a hour or so. However, he shies and spooks when I least expect it. I was wondering if there was any way I could help him have steadier nerves through a change in nutrition.
There have been few studies on the effect of energy sources on the reactivity of horses. The one major study that had significant results compared a high-fat diet to a classic low-fat diet, finding that horses were less reactive when fed a high-fat feed. You’re feeding a high-fat, high-fiber feed, so it would theoretically help him be less reactive. Obviously, the feed is not having the desired effect for you.
That is not to say that you need to change the diet; in other aspects it appears that you are doing the right thing for him. You may consider adding a vitamin and mineral supplement to balance the supply of micronutrients, because you are feeding below the recommended feeding rate of the concentrate feed.
There are some nutrients or herbs that are thought to have calming effects on horses like magnesium, thiamine (B1), L-tryptophan, inositol, valerian root, and chamomile, just to name a few. In-depth studies on these nutrients and herbs have not been performed in horses. There are numerous combinations of these products available on the market. Whether or not they have a calming effect depends on the individual horse, and how a horse will respond can only be determined by trying different products.
Some horses are just wound a little tighter than their peers, and regardless of what you feed, they are going to react as they see fit to protect themselves.