Diarrhea in Senior Horses

The second senior horse I took in was a 27 year­-old palomino gelding named Thunder.  He had chronic diarrhea for years.  While with the previous owner, the vet could not find a cause.  They started him on a probiotic, which seemed to help.  They even tried worming him with Moxidectin, which is the most potent of all wormers.  (You do not want to get the dosage wrong, and it is not typically recommended for senior horses).  They thought that perhaps the cause of the diarrhea was a worm that only Moxidectin could kill.

The year or two before I took him, I heard that he was having problems with diarrhea.  I did some research and learned that if you have a senior horse with diarrhea the first thing to eliminate as a cause is the teeth.  An equine dentist, who has extensive training beyond vet school can give a complete evaluation of the mouth and teeth.  An equine dentist will catch things a general equine vet may not.

When I took Thunder into my care the first thing I did was take him to the dentist.  The dentist said his teeth were completely worn out and could no longer chew hay.  The molars in horses should be completely flat and when the top arcade of molars meets the bottom arcade it grinds hay.  Thunder’s teeth were “cupped out”, meaning there was no longer a flat surface, but rather a cupped surface.  When he went to grind hay he couldn’t.  The dentist said that if large pieces of inadequately chewed hay were to get all the way to the colon, they could irritate it and cause diarrhea.  It looked like that was what was happening with Thunder.

I immediately took Thunder off hay and fed him soaked hay pellets.  Within a week his manure normalized, and there was no sign of diarrhea.  I even weaned him off the probiotic, and the diarrhea hasn’t been back. It’s been 2 1⁄2 years.

I asked the dentist if the present condition of Thunder’s teeth was preventable.

“Yes,” he answered.

“When would have been the last chance to start seeing him before we would end up with worn out teeth?”

“Ten years ago.”

Why does this all matter?  It’s cheaper to feed high quality hay than it is to feed hay pellets.  It’s more convenient to feed hay than it is to soak hay pellets a few times a day.  While I don’t regret a single moment figuring out what Thunder needed and then providing it, if different decisions were made 10 years ago, and the information was in the hands of the horse owner, then Thunder could have been spared the years of chronic diarrhea and the resulting toll it took on his body.

If you have a horse, consider seeing an equine dentist as part of your horse’s care team.  Don’t wait until they are old and having serious issues.  Prevention is key.  The health and longevity of your horse depends on it.  And the best part of all, you will have more years to enjoy your horse.

The day I picked up Thunder.  Notice the dirty hocks.  It is from the chronic diarrhea.

The day I picked up Thunder. Notice his dirty hocks from the chronic diarrhea.



6 days post diet change. Normal manure.


20 days post diet change. Notice his clean hocks. No more diarrhea.


  1. Going through the same thing now with my rescue horse…. teeth are very worn down and very long fibers in her stool. Diarrhea for the last few weeks and have worked twice. Fecal egg count was negative so switching from soaked beet pulp to senior feed with alfalfa pellets to see if that does the trick. All soaked and gradually obviously…wish me luck. Love my old girl ❤️

    • I hope you find what works. It can definitely be some trial and error. I tend to shy away from senior feeds because they are grain based, and grain can cause problems for the gut long-term because of its inflammatory properties. Here’s a wonderful article on the topic: https://theequinepractice.com/why-horses-should-not-be-fed-grain/?

      I was pleasantly surprised with the soaked hay pellets. They’ve worked so well with weight gain and no diarrhea that I’ve never needed to go to grain.

      Here’s another article I recently wrote on feeding seniors that gives a more complete picture. http://seniorhorserehab.com/senior-horse-care-tips/

      Good luck with your rescue and finding just what works for her. She is lucky to have you!

      • What kind of hay pellet? Alfalfa or what? Do they have Timothy hay pellets?? Thunder has exactly the same problem as my horse, (his name is Thunder too!!) My horse quids very badly and has chronic diarrhea. I am at my wits end trying to fatten him up before winter comes. Help!!

        • Hi Nancy,

          I use soaked timothy hay pellets and soaked orchard grass hay pellets. It’s basically the replacement for hay. (You can also use soaked hay cubes. The pellets worked so well for me I never bothered with trying the cubes, but cubes are an option). I feed about 10-15% of the diet in alfalfa (assuming there’s no serious metabolic issues going on). For my Thunder he was 1000 lbs and maintained his weight on pasture and pellets. In the summer he ate 10 lbs of pellets per day (I split it between 2 or more feedings per day, the more feedings the better). In the winter it was 15 lbs. With this amount he maintained his weight. I did not give him access to any hay. His inability to chew it adequately is what caused the diarrhea for him.

          Here’s another article I wrote on feeding seniors that might provide some more info for you. http://seniorhorserehab.com/senior-horse-care-tips/

          Good luck. I’d love to hear how it goes.

          • Hello, I am so excited to try your suggestions. I got the Redmond salt block, and also some Timothy and alfalfa pellets. Will start the new program tomorrow. No grain!! I am saying my prayers and hope my Thunder gets rid of his diarrhea and starts to gain weight. Winter will be upon us soon enough. Will keep you posted and thank you very much with all my heart!!

          • Hi Nancy, I hope the diarrhea clears up quickly. For my Thunder it was better within 5 days of the new diet and no hay, and by day 10 the manure had been normal for several days, so I knew we were out of the woods. He was diarrhea free to the day he died nearly four years later. No matter what happens, everything your Thunder does is info that will steer you to the ultimate cause of the diarrhea for him. He sounds very similar to my horse, and it would be wonderful if these changes did the trick and you could relax and just be able to enjoy him. I’d love to know how it goes. Good luck!

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