Do gastric ulcer medications affect digestion?

A racing client asked me this recently and it reminded me that when I was studying during my PhD tenure, we had looked at the effect of pre-incubating grains in pH 3.7 equine stomach fluid on the digestion of starch from those grains.

And what we found was that starch from grains that were exposed to equine stomach fluid before being digested by small intestinal enzymes was between 17% (extruded rice) and 104% (cracked triticale) MORE digested than starch that wasn’t exposed to the stomach fluid.

So, the stomach fluid was having a definite positive influence on the digestion of starch.

We also incubated the grains in pH 3.7 hydrochloric acid to allow us to determine how much of this increased starch digestion was due to the stomach acid and how much was due to the protein digesting enzymes that are present in stomach fluid.

These protein digesting enzymes would be starting protein digestion and making access to the grain starch easier for the starch digesting enzymes in the small intestine. And therefore, potentially increasing starch digestion.

What we found was that incubation in hydrochloric acid only increased the digestion of the starch from extruded rice by just 3.5% (compared to 17% when incubated in actual stomach fluid) and by only 23% (compared to 104%) for cracked triticale.

So, while the acid did increase digestion, it wasn’t nearly to the same magnitude as stomach fluid itself, showing that it is both the acid and the protein digesting enzymes (and possibly other factors) that were increasing digestion!

The thing to remember though is that the protein digesting enzymes in a horse’s stomach fluid rely on the stomach acid to activate them.  

So regardless of whether the improved digestion was due to the acid itself or the protein digesting enzymes, if you stop acid production using ulcer medications, you will lose both the acid and the enzymes. And this is likely going to reduce starch digestion.

This means, if we use medications like ranitidine and omeprazole to reduce gastric acid secretion in horse’s we are very likely reducing the digestion of at least some nutrients further down the gastrointestinal tract. With starch being one of them.

What to do???

Well, if your horse has ulcers this is by far the most important consideration, you need to medicate to get rid of the ulcers as quickly and as effectively as you can.

BUT, once the ulcers are gone it is recommended you use good management practices to keep your horses chewing, their stomachs full and buffered with saliva and their minds calm instead of constantly using medication to prevent ulcers.

That way you are allowing their gastrointestinal tract to function the way it was designed and allowing the digestion process to be as effective as possible.

If possible, it may also be wise to reduce grain (and therefore starch) intake while your horse is being medicated to treat ulcers. 

Reduced starch digestion in the small intestine can then lead to increased starch fermentation in the hindgut which will cause acid accumulation and hindgut microbial dysbiosis… but that is another story for another day!

There is more info on feeding to prevent ulcers in our article ‘Preventing gastric ulcers in horses’.

And if you have more detailed questions about all things feeding and gastric ulceration, be sure to ask Dr Nerida AI.