Hay Belly: What It Is & How to Eliminate It

Have you ever seen a horse that looks overweight, yet can also appear skinny at the same time? Alternatively, have you seen a horse that looks pregnant with a large bulging side, but is, in fact, a gelding with a distended abdomen? This is a condition termed “hay belly” and is usually a result of feeding a horse poor quality hay. The abdomen is distended in these horses because of gut fill and because the forage is taking much longer to digest. Horses suffering from hay belly are poor performers and just appear unwell. It is a situation that horse owners need to avoid.

What Are the Signs of Hay Belly?

Both male and female horses can suffer from hay belly. As stated, the most obvious sign is when looking at the horse from the front, a non-pregnant horse looks pregnant, with the belly distending outwards. Horses suffering from hay belly will also appear slim throughout other portions of its body. These include:

  • Poor topline muscling.
  • Ribs are visible and easily seen.
  • Lack of condition (body fat) throughout the body.
  • Rough or dull coat.

Overall, a horse suffering from hay belly will appear obese due to its distended belly. Yet, upon closer inspection, often the horse really is skinny and just has a “bloated” appearance. It is important to remember horses that have a hay belly are not “fat” or overly conditioned. Rather, it is a product of a digestive system full of low-quality forage that is taking much longer to digest.

What Are the Causes of Hay Belly?

The primary cause of hay belly is the feeding of poor-quality and overly mature hay. As forage matures, the plant becomes more fibrous and less nutritious for the horse. It also becomes higher in neutral detergent fiber (NDF) and acid detergent fiber (ADF), which are measurements of fiber. These include lignin, cellulose, and hemicellulose. A forage analysis can determine the balance of NDF and ADF in a forage. In general:

  • High quality forage has an NDF value of 40-50% and ADF 30-35%.
  • Moderate quality forage has an NDF value of 50-60% and ADF 35-40%.
  • Low quality forage has an NDF value of >60% and ADF >40%.

Forage that is prickly to the touch, looks stemmy and is high in NDF/ADF is devoid of the many important nutrients and energy (calories) that a horse needs. It leads to an equine digestive system that slows down to try to extract as many nutrients as possible. Thus, the horse’s belly will distend with gut fill.

Another byproduct of feeding low quality forage is the deficiency of adequate nutrition. This leads to a lack of healthy appearance, lower body condition score, poor muscling and rough hair coats. Even in instances when the horse is being fed a quality feed, they will likely still appear malnourished. This is because forage makes up the bulk of a horse’s diet and is where horses will receive most of their nutrients. Most horse feeds are formulated to fill the nutritional gaps that quality forages will not meet. They typically are not meant to completely replace the nutrients from hay. Only special feeds manufactured and marketed as a complete hay replacements, or senior feeds, can do this. 

In some circumstances, a horse that is fed good or high-quality hay can also suffer from hay belly. In these instances, it’s usually because the horse’s microbial population is not properly balanced, thus having difficulty and taking longer to digest feedstuffs.

How Should I Alter My Feeding Plan to Avoid Hay Belly?

If feeding a low-quality hay, it is obvious that your horse should be switched to a higher quality hay. This will ensure your horse is receiving enough nutrients and their large, distended belly should subside. However, it is important to remember that when you switch anything in your horse’s diet, you want to make the change slowly. The number one cause of colic is a rapid change in a horse’s diet. Thus, it would be worth your time to review our article on Safely Transitioning Your Horse’s Diet and adjust your feeding plan accordingly.

In addition to improving your horse’s hay, it may be worth feeding a pre- and probiotic to help reestablish a healthy population of gut microbes. This is especially important for those rare instances when a horse has a hay belly, but has been eating quality forage. Quality horse feeds, including Tribute®, should already have added pre- and probiotics in them. If those are not available to you, adding a pre- and probiotic supplement, like Equi-Ferm XL® or Constant Comfort®, will be beneficial.
This would also be a good time to review which horse feed you are feeding. Be sure that you are feeding a quality feed that is meeting, but not overly exceeding, your horse’s energy and nutrient needs. You may find that your horse has been trying to compensate their low-quality hay with a higher calorie feed. Thus, once the switch is made to a high-quality forage, the higher calorie feed may no longer be needed.

Finally, it is worthwhile to review your internal parasite control plan. Sometimes a distended belly is an indication of a parasitic infection. It is important to discuss this with your veterinarian and have them conduct a fecal egg float to see if your animal needs treatment.

Take Home Message

Hay belly is most commonly caused by feeding horses a low-quality forage that leads to gut fill and extended digestive times. To alleviate hay belly, owners are advised to check their forage quality and change to higher quality forage, as well as evaluating other aspects of their feeding plan. For any horse that experiences hay belly, it is worthwhile to ensure their animals are receiving pre- and probiotics for a healthy gut biome. It is also worthwhile to discuss with your veterinarian your horse’s internal parasite control plan. If you have any questions or concerns about your feeding plan, please feel free to contact us anytime!

Article By: Chris Mortensen, Ph.D.
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