A: While it’s true that it is typically best to avoid feeding horses concentrates (especially those high in starch) within a couple of hours of riding due to the effect this can have on available metabolites during exercise, allowing access to forage has a number of benefits. Remember horses are designed to eat fibrous plant material almost constantly, while at the same time traveling considerable distances.
As a result of this constant forage consumption, horses have evolved to secrete gastric acid into their stomachs on a continuous basis. Acid is secreted whether they are eating or not and is needed to activate enzymes involved in protein digestion. The act of chewing causes the release of saliva, which contains sodium bicarbonate and calcium—both of which act to buffer stomach acid. It’s a brilliant system, because the constantly secreted stomach acid is buffered by the continuous release of saliva from chewing.
But what happens when, instead of continuous access to forage, we meal-feed our horses? The stomach acid is secreted as always, but there is no longer a steady saliva supply. That’s because most horses finish their allotted hay meal in at most a couple of hours unless eating out of a slow feeder. This leaves the stomach environment to become increasingly acidic and raises ulcer risk.
If we happen to come and ride our horses at this time, not only is there a more acidic environment in the stomach, but there’s also less fiber to prevent movement of stomach fluid. The stomach is never completely full, and the fluid portion of the stomach contents sits at the bottom of the stomach with the larger feed particles such as chewed hay floating on top, forming a sort of mat. This mat helps to prevent the stomach acid from sloshing around. The mat is particularly important because the area of the upper stomach, above the level of the stomach acid, is the most at risk of ulcers and has very little protecting it other than this mat suppressing acid movement.
The glandular cells in the lower two thirds of the stomach that secrete acid also secrete mucin and bicarbonate, so they are protected (note that ulcers can still occur here but they are less common). But the cells of the upper squamous portion don’t secrete acid and therefore have very little protection. They’re not designed to come in to contact with stomach acid. As we ride the stomach acid sloshes about and—if there is not a good fibrous mat—it will come into contact with those unprotected squamous cells, leading to an increased risk of ulceration.
If it has been several hours since your horse last had access to hay or other forage, I recommend offering some hay prior to riding. While consuming forage might increase body weight, which some believe is a negative attribute for horses needing to work at speed, researchers have showed that feeding small amounts of hay or grazing prior to exercise doesn’t negatively impact performance.
If you have a choice in hay available, I recommend offering access to alfalfa before exercise. The reason for this is that studies have found that alfalfa’s high calcium and protein content have additional buffering capacity, which researchers believe help further reduce ulcer risk over other forms of hay. If your barn does not feed alfalfa or you don’t want your horse to get a full flake of alfalfa hay, then feeding a pound or two of alfalfa pellets is likely to be sufficient. You could offer these while you’re grooming and preparing to ride.