Q. My horse often passes gas under saddle. Typically, it is when we start cantering. Why does this happen, and should I be concerned? He seems very healthy, eats and drinks well, and has a happy disposition.

A. Some horses do pass gas when ridden but otherwise are not particularly gassy. We have one at the barn where we ride, and it’s not uncommon to hear a large fart coming from the arena, and we can always guess that this horse is being ridden. Like your horse, he’s also a very happy and otherwise healthy horse.

The most likely cause of a horse passing gas when ridden but not during rest is that the movement of exercise causes the rate of gut motility to change. Normally, movement through the gut is fairly steady, and so gas passes slowly and goes unnoticed. However, with exercise the rate of movement goes up, and gas in the digestive tract moves more quickly, such that a large amount of gas is passed at once rather than slowly over time.

Gas in the digestive tract is perfectly normal. While we might not like to admit it, we all fart. Certainly, some foods in the human diet are known to more likely result in gas than others, such as cruciferous vegetables (cabbage, Brussel sprouts, broccoli, etc.) and beans. So, it’s possible that your horse’s gas is also related to the diet.

The gas being released when worked is likely the result of feed being fermented in the horse’s hindgut by the microbial population that lives there. This is a perfectly normal and desirable process, but sometimes diet can result in more rapid fermentation and greater quantities of gas being produced. If your horse’s diet is rich in compounds that result in the proliferation of gas-producing bacteria, then  more gas might be produced.

Feeding large meals high in starch or sugar can cause gas production, because the quantity might be too much for the small intestine to absorb. The excess escapes to the hindgut where it’s easily fermented by the hindgut bacteria, creating gas. Eating large quantities of spring grass can also cause this. Sudden hay changes might also result in gas production while microbes adapt to the chemical composition of the new hay.

Assessing the diet of a horse that passes a lot of gas to rule out any of these potential issues is worthwhile. Making the diet fairly bland and avoiding high-starch feeds and sudden changes to the diet might help. Feeding a good prebiotic such as Saccharomyces cerevisiae yeast that can help stabilize the hindgut microbial population might also help.

Passing gas is certainly more desirable than not passing gas, because having it build up can sometimes cause displacement of the digestive tract, resulting in discomfort and colic. While gas buildup can be a sign of blockage in the digestive tract and indicate trouble, if your horse is passing gas loudly under saddle on a regular basis and is otherwise healthy and happy, you have nothing to be concerned about.