Hindgut Acidosis in Horses


What does hindgut acidosis in horses MEAN? And how can this affect your horse? And how do you know if your horse has hindgut acidosis? Or hindgut ulcers? And what can you do about it? Lots of questions; here are some answers.


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But first, some anatomy of your horse’s digestive system.


  • Let’s briefly review your horse’s digestive system, from rooter to tooter. It all starts at the mouth and continues through the pharynx, where the respiratory system and digestive systems meet.


  • Then, the esophagus and stomach. Incidentally, this is usually where gastric ulcers are found. The foregut is comprised of the stomach and the small intestine. Most of your horse’s nutrient absorption happens in the foregut.


  • Next is the hindgut, which has many parts. The cecum, the large colon, the small colon, and the rectum make up the hindgut. This is where water is reabsorbed, microbes ferment, and manure is “made” and passed.


For more detail on your horse’s digestive system, this riveting article has you covered.


two x marks indicating where to check gut sounds on horses

Listening to your horse’s gut sounds gives you an idea of what’s happening inside – know the normals!


What is hindgut acidosis?


  • Let’s dive into the hindgut and see what’s going on concerning acidosis and pH. A horse’s gut pH measures how acidic the environment is. The measurements are on a scale of 1 to 14, with 7 being neutral, like water. Values closer to 1 are more acidic, and values closer to 14 are more basic.


  • A horse’s hindgut usually has a pH of about 6.5 to 7, so reasonably neutral. In the hindgut, there are also several types of microbes, each with its own food preferences. In the simplest of terms, there’s the group of fiber-loving microbes and the sugar-loving microbes.


  • The fiber-loving microbes are responsible for fermentation and filling your horse’s energy needs. These guys love the neutral-ish conditions of the balanced hindgut. The other group of microbes LOVE sugars and eat them up. When these sugar lovers “poop,” their by-products are acidic and can lower the pH of the hindgut. As the pH becomes more acidic, these sugar-loving microbes thrive! It becomes a vicious cycle.


And this is how the problems begin


  • But… the fiber-loving microbes can’t tolerate the lower pH. They will begin to die and release endotoxins upon their death.


  • So – now we have an acidic hindgut, AKA hindgut acidosis, with many dead microbes and their endotoxins floating around. The acidic nature of the hindgut now will also create openings in the lining of the hindgut. This allows the endotoxins to escape into the bloodstream, where they can create all sorts of problems, including colic and laminitis.



gray horse with fly mask grazing on a hill

All in moderation!


What about ulcers in the hindgut?


  • Hindgut ulcers are another problem. Complicated by the fact that they are trickier to diagnose than gastric ulcers, which can be seen during endoscopy. These hindgut ulcers happen while the lining of the intestinal walls and mucosa start eroding and sloughing away.


  • Ulcers in the hindgut are prevalent in roughly 60% of horses, depending on what study you read. It’s understood that hindgut ulcers are more likely to happen in performance horses. It’s also suspected that gastric ulcers and hindgut ulcers have some common denominators, like the use of NSAID’s (bute and banamine). Other factors include diet, how you feed your horse, your horse’s stress level, and even parasites.


What are the signs of acidosis and hindgut ulcers?


This list is long and mostly vague. You might find that your horse is showing these signs:


  • Lethargy
  • Becoming a picky eater
  • Performance loss
  • Vices like weaving, cribbing, wind-sucking, teeth grinding
  • Acting colicky
  • Laminitis
  • Tying up
  • Longer recovery time after exercise
  • Lack of bloom – dull coat, no eye sparkle
  • Anemia
  • Mystery “offness” or lameness in the hind quarters
  • Abnormal manure or diarrhea
  • Unwillingness to perform, bend, or collect


Tests your vet can do to help determine what’s going on:


  • It’s relatively easy for your vet to test your horse’s fecal pH, which gives you an idea of the acidity levels in your horse’s gut. There are also fecal blood tests, which tell your vet if there’s any blood in your horse’s digestive tract.


  • Ultrasounds of your horse’s colon can also help determine what’s going on in your horse’s hindgut.


  • Your vet will also need details of your horse’s feed, feeding practices, and exercise and turnout routines to put the big picture together.


picking up manure in a pasture

Your horse’s manure can tell you a lot, too.


What to do about hindgut acidosis in horses.

Your vet and equine nutritionist can help you design a program to help your horse.


  • Medications may be prescribed depending on the overall state of your horse’s hindgut. Omeprazole for gastric ulcers does nothing for hindgut ulcers; sucralfate is used instead.


  • There may be supplements and diet changes to consider as well. For some horses, the ability to tolerate long-stem forage is decreased, and new forage options need to be considered. For other horses, the amount of long-stem forage needs to be increased. There are also hindgut supplement programs to consider, as well as using a hindgut buffer supplement. I recommend researching the best ones; there are many supplements based on marketing with zero science to back them up. I use a KER hindgut buffer; it’s been studied with proven results. Probiotics and probiotics may help also.


You may need to change how your horse eats as well.


  • Because this all starts with starch and sugar hitting your horse’s hindgut in large volumes, it’s important to make sure this is all spread out.


  • Feed fortified feeds in several small meals. Generally speaking, most horses should be getting less than 5 lbs. a day of fortified feeds or grain meals, and the safest way to feed them is several times a day. More on this topic can be found here.


  • Feed a hay meal before a “grain” or feed meal. This allows the stomach to have some filler in it, so that grains and feeds don’t hit the stomach and zoom to the small intestine and the hindgut. It gives your horse more time to break down the food, so that the hindgut isn’t overwhelmed with starch and sugars. More on this topic here.


  • Make sure you introduce pasture slowly to your horse. There’s an adjustment period, just as switching foods over a few weeks is a good idea. It’s a new diet, and your horse needs time to adjust. Some ideas on how to do this can be found here.


  • Use a grazing muzzle. This just might save his life! Muzzles give your horse a chance to do his horse thing in the pasture, move around, and chill with buddies, all while providing a SLOW way of letting sugars and starches ease into your horse’s hindgut.


lush pasture and horse using a grazing muzzle to eat

Horses quickly figure grazing muzzles out. This is the Greenguard Equine Muzzle.


Monitor changes to your horse’s pasture and feeds


  • Take your horse off pasture when the grass is stressed and producing too much sugar. This happens in early spring and fall when there are growth spurts of grass. It also happens when nights are cool (below about 40) and days are warm. The hot afternoon sun also stresses out pastures. So does mowing to a degree. Learn what type of grass your horse is eating, how and when it grows, and turnout accordingly. More on the NSC (“sugar”) values of grass and how they fluctuate here.


  • Use slow feeders and hay nets, so your horse nibbles all day. This is the same premise as a muzzle; it allows your horse to eat more naturally. Nice and slow, keeping the digestive system balanced and happy, and moving along.


  • Avoid raw grain diets; these allow too much starch to reach the hindgut. Horse feeds are processed to allow your horse’s foregut to retrieve what it needs before sending a bunch of sugars and starches to the hindgut. It may seem more “natural”, but raw grain foods for horses are definitely not the best. Think of it this way – a horse fed raw corn, wheat, or barley will have 75% of that meal’s starch land in the hindgut, where those sugar-loving microbes will go to town. Feeding grains processed into pellets or extruded or micronized eliminates this problem.


three small hole hay nets in a hay loft

Haynets and slow feeders are important.


See what you can do about your horse’s stress level


  • Provide lots of turnout if possible. It doesn’t have to be pasture; it can be dry lots. Make sure that horses can see each other to help reduce stress.


  • Use a sensible and fair training program. Weekend warrior horses ridden hard and standing around the rest of the week will be stressed. So will the athlete that is in training for a bit event. So will the horse that hates his job for whatever reason. Fitness happens over time with a careful program.


  • Be fair when you are trailering your horse. Travel and shows and ever-changing environments can create stress for your horse.


For more on stress in horses, this article has you covered.




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Safety break-away halter for grazing muzzles.



The best muzzle in the land – order one here! Also in raspberry and black colors.

Use code 15PROEQUINE for a lovely discount!

This slow feeder for pellets and grains helps your horse take his time eating. 

Another style of slow feeder for pellets and grains

Durvet/Equine D-Pre-Vent Feeder- Black 20X12 Inch – this is a slow feeder for pellets and bagged feeds

EquiShure is a hindgut buffer that can help Cushing’s in horses as well as IR horses to balance their hindguts.


Starch Guard Hindgut Buffer

Slow feeder hay bag


Another style of hay bag

Small opening hay net

Traditional slow feeder with smaller openings



Thank you!








hindgut acidosis in horses