What To Do About a Mule’s Hay Belly

An equine nutritionist explains why you should consult your veterinarian and test hay quality if your mule (or horse) has a hay belly.
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A hay belly can be caused by health problems or a diet that is difficult for your mule or horse to digest. | Photo: iStock

Q. What can I do to help reduce my mule’s hay belly? I’ve heard I need to increase her protein intake but not give her alfalfa. Is this true?

A. Hay belly is a common issue in both horses and mules, and you are right to be proactive about addressing the issue. A hay belly is characterized by a distended abdomen and can occur in equids that are both under- and overweight. It is important to note that an obese equid can appear to have a larger abdomen, therefore nutritionists recommend that you regularly assess body condition score so you are familiar with the areas of the body where fat is deposited.

The nine-point Henneke scale is commonly used and evaluates six key body regions (neck, withers, shoulder, ribs, back, and tailhead). It is crucial to determine your mule’s body condition score because he or she can have a hay belly and, again, be underweight—in fact, this is common.

There are a few different factors that can play a role in the presence of a hay belly, including underlying health issues or even a high parasite load. Therefore, the first step should be to have your veterinarian evaluate your mule and rule out any of those potential problems.

The next important step is having your hay analyzed for its nutritional content. The most common cause of the hay-belly appearance has to do with the fiber content of the hay the animal is consuming. You are correct that your mule might need additional protein if your forage is low-quality; however, without a hay analysis, blindly adding protein is not recommended. Working with a qualified equine nutritionist or sending in your hay for analysis will give you valuable information on the digestibility of that forage for your mule.

Generally, donkeys and mules digest protein more efficiently than horses and can do well on a forage that might not suit a hard keeper. However, when you have large proportions of lignin, neutral detergent fiber (NDF), and acid detergent fiber (ADF), it indicates poor digestibility and can contribute to a hay belly.

The ADF is a measurement of cellulose and lignin while NDF is a measurement of lignin, cellulose, and hemicellulose. Because lignin in not easily digestible for horses, forage that is high in ADF, NDF, and lignin takes longer to digest, increases gut fill, and contributes to the hay-belly appearance. If the NDF is greater than 60%, and the ADF is greater than 40%, that is considered a poor-quality forage. When NDF reaches 65% there is concern of impaction colic for horses as well. Therefore, testing your hay to collect this information is crucial for determining how to remedy your mule’s hay belly.

Based on the hay analysis, the recommendations could be to find a different hay source, or alfalfa could be an option if your mule is underweight and needs additional protein. However, due to donkeys’ nutritional efficiency, alfalfa is not normally the best option, simply because it is high-protein and high-calorie—which these animals typically don’t need.

Adding an easily digestible fiber source might help reduce your mule’s hay belly, and occasionally gut-support supplements can be beneficial. However, be sure to evaluate the research on various products or consult a nutritionist to ensure you are feeding a supplement that is backed by scientific evidence.

Take-Home Message

Overall, equids have evolved to consume fiber, however, we still need to be cognizant of how digestible that fiber is for the animal. Have your veterinarian rule out underlying health issues, and then test the hay so you are equipped with nutritional information to base decisions on. With this additional information from your hay analysis, an equine nutritionist will be able to assist you in choosing a better fiber source if needed and ensuring that your mule’s protein requirements are being met.


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Written by:

Madeline Boast completed her master’s in Equine Nutrition at the University of Guelph and started an independent nutrition company known as Balanced Bay. She has worked with a variety of equids—from Miniature Ponies to competing Thoroughbreds. Boast designs customized balanced nutrition plans that prioritize equine well-being, both for optimal performance and solving complex nutritional issues and everything between. 

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