Horse caretakers want the best for their equines, and making sure their diet supports their gut health will help keep them happy and healthy. Your horse’s digestive system has a long-reaching effect on his health since the gut is responsible for 70% of his immune system function. Let’s explore some factors that can positively or negatively affect your horses gut health.


For digestive wellness, horses should consume 2% of their body weight in forage. Hard keepers or horses in heavy work may need closer to 3%. To avoid digestive concerns, never feed less than 1.5% of your horse’s body weight in forage. For a 1,000 lb horse, that’s 15 lb of forage per day. Feeding less than this can put your horse at risk for ulcers, colic, or diarrhea.

A more stable and diverse microbial population results when a horse is fed a forage-only diet, especially when compared with a sugar- and starch-rich ration. Hay bales and individual flakes of hay can vary by weight. If your horse is on restricted hay, it is best to weigh the hay to ensure you are feeding 1.5% of his body weight. A luggage or fish scale comes in handy for weighing bales or flakes of hay.


Grains and concentrates should be limited to 4 lb to 5 lb per meal. Putting a limit on meal
size helps ensure starch is digested in the small intestine. If it isn’t, it ends up in the large intestine where it is fermented. As starch fermentation occurs, the production of lactic acid and volatile fatty acid increases, which reduces pH in the hindgut. This decrease in pH causes the good fiber-fermenting bacteria to die off and release endotoxins. Cell walls are then damaged, releasing endotoxins into the bloodstream, which can lead to increased inflammation, ulcers, or laminitis.

Multiple studies have also linked high-starch diets that alter the equine microbiome to increased behavioral reactivity. Small, frequent meals can help reduce the horse’s risk of developing these issues. Starch has its place for some horses, especially those who cannot consume enough forage to meet daily energy requirements, such as horses in heavy work. The key is to feed in moderation, 4 lb to 5 lb per meal.


A horse’s digestive system is designed for a slow and almost continual intake of fiber. Long-stem forage requires your horse to chew for a longer duration than hay pellets do. This longer chew time produces more saliva, which is your horse’s natural stomach acid buffer. When horses stop chewing, they also stop producing saliva, yet they continue to produce stomach acid 24/7. For horses who need to be on restricted hay – e.g. a horse that gains weight on very little hay – the use of slow feed nets can prolong chew time. Constant chewing means a comfortable tummy.


Rapid diet changes will cause changes in the microflora of the hindgut. These changes can adversely affect digestive health, leading to diarrhea, colic, and other forms of digestive upset. A change in hay within the previous two weeks can increase the risk of colic.

  • As a general rule, the larger the volume of feed, the longer the introduction should be. Since forage makes up the majority of your horse’s diet, take the most time introducing new hay, over seven to ten days.
  • Next would be your bowl feed (grain, concentrates etc.), which should take at least five to seven days.
  • Lastly are supplements. Since the feed rate on supplements is usually very small, they only need a three to four-day introduction. A longer introduction is always a better introduction.


Fun fact: a horse’s weight consists of 70% water. For your average 1,000 lb horse, that’s 700 lbs of water! When your horse does not drink enough, the contents of his gut can become too high in dry matter, which puts him at risk of developing impaction colic. Horses will drink five to ten gallons of water per day. If you notice your horse does not drink a lot, adding two tablespoons of salt to his diet will help. He should also have free access to a plain white salt block. Horses consume less water in the winter. Help them drink more by keeping the water around 40°F to 60°F. In one study, horses drank 38% to 41% less cold water compared to water at 66°F.


Unfortunately, antibiotics do not know the good bugs from the bad, and will decrease the hindgut’s microbiota. The damage can last a while. In one study, the microbiota was more similar to baseline 30 days after treatment than it was in the Day 5 or Day 14 samples, but was not completely back to normal (Costa et al, 2015).

NSAIDs increase the risk of developing right dorsal colitis and ulceration throughout the gastrointestinal mucosa, as well as in the mouth and esophagus. Every horse may tolerate NSAIDs differently, but there will be some effect on the microbiota.


Many feed items will benefit your horse’s digestive system. Here are four:

  1. Yeast: The most common yeast in horse feeds is Saccharomyces cerevisiae. It can help normalize gut pH and support the growth ofbeneficial fiber-digesting microbes.
  2. Beet Pulp: This fibrous portion of the sugar beet remains after the sugar has been removed. It ferments like hay in the hindgut and does not produce a blood sugar spike the way grains or concentrates can do. Beet pulp can absorb four times its weight in water; therefore, it’s an excellent way to get additional water into your horse’s system. It also acts as a prebiotic.
  3. Omega-3 Fatty Acids: These can be found in flax, chia, camelina oil, fish oil or algae.
    Omega-3 fatty acids can support anti-inflammatory mechanisms in the body and boost your horse’s immune system. Positive effects may also be seen in the coat, hooves, joints, airways, and reproduction.
  4. Prebiotics and probiotics: Prebiotics are non-living substances fed to support and nourish good microbes. Probiotics are live beneficial organisms that may enhance the existing population of helpful gut microbes and improve digestive health. When shopping for a Probiotic, ensure each serving provides Colony Forming Units (CFUs) in the billions. This information will be listed on the guaranteed analysis.


When we think of stress in our horses’ lives, we typically think of heavy workloads, competitions, or trailering. However, many other factors can create stress. Some examples are weather (heat stress), change in routine (e.g. being late to feed your horse), and a horse buddy leaving or a new one arriving. Stress has well-documented physical effects on a horse and can lead to ulcers, diarrhea, or colic. Stress will also suppress the immune system, leaving the horse vulnerable to illness.

Your horse’s gut plays a role in so many aspects of his well-being. Feeding a diet to support a healthy gut will help him thrive. A healthy gut is a healthy horse!

Nicole Sicely is an independent equine nutritionist who owns Custom Equine Nutrition, LLC. Her passion for equine nutrition started in 2002, the day her Tennessee Walker gelding, Chance, was diagnosed with PPID (Cushing’s Disease). Nicole formulated the forage balance, Vermont Blend, which is recommended by veterinarians and farriers across the US. She resides in Vermont with her husband, two kids, and three horses (