Oats in Manure: Is My Horse Getting the Nutrition He Needs?

Q: I can see fully formed oats in my horse’s manure. Does this mean he’s not digesting his feed and, if he’s not, then is he not getting the nutrition he needs (or am I wasting my money on textured feed that includes oats)?

A: This is a great question and one I get asked often. The short answer? It might or might not mean your horse isn’t digesting the oats. You won’t know without further investigation, and that means getting your hands in some manure.

What at first glance might appear to be fully formed grains of oat may, in fact, be just the remains and outer indigestible hull. To find out, get a few pieces of oat from the manure and press them between your finger and thumb, and see what’s inside. It should be empty, which will confirm that your horse has digested all the good stuff and just the hull remains. However, if white starch comes out when you squeeze them, this means your horse hasn’t fully digested the oats.

Starch digestion should take place in the horse’s small intestine. If this doesn’t happen, it will pass down the digestive tract, arriving in the hindgut where it might have a negative impact on microbial fermentation. Therefore, if oats containing starch are present in your horse’s manure, then you should change his diet to ensure undigested starch is not reaching the hindgut.

The starch in oats, like that in other grains such as barley and corn, is packaged up deep inside the grain. For the small intestine’s digestive enzymes to access the starch, they have to penetrate the grain’s outer layer, or hull, and then the aleurone, which is the outermost layer of the endosperm (the part of a seed that stores nutrition for the developing plant embryo). Finally, they have to break through the cell walls of the endosperm to reach the starch. Chewing the grain helps break down the hull, allowing digestive enzymes access to the interior parts of the grain.

Horses with good dentition should do a more-than-adequate job of breaking the hull when they chew, which is why it’s fine to feed whole oats. However, if you’re feeding whole oats and find grains with starch still inside, this could indicate that this particular horse needs oat grains that have been through some kind of processing that breaks the hull, such as crimping or rolling. 

Whole oats include intact hulls, which protect the grain’s endosperm from oxygen and the possible breakdown of numerous nutritional components. So whenever possible, feed horses whole oats.

In contrast, you should never feed horses whole barley or whole corn, because the form of starch in these grains isn’t very digestible in the equine digestive tract. These grains first require heat processing (e.g., steam flaking, micronizing, or extruding). The heat significantly alters the starch’s physical composition, which improves its digestibility. Doing so reduces the risk of undigested starch reaching the horse’s hindgut.

Whether oat starch’s presence in manure indicates the horse’s digestive tract isn’t absorbing other commercial feed nutrients is hard to say. I’d tend to assume that the presence of oat starch solely means that oat starch is being poorly digested. However, if your horse is struggling to maintain weight or shows signs that suggest inadequate absorption of other nutrients (such as protein), it’s possible that there may be a larger malabsorption issue that should be investigated by your veterinarian. If your vet determines your horse has problems with nutrient absorption from the small intestine, she and an equine nutritionist can work with you to create a diet that contains sources of more bioavailable nutrients and focuses on hindgut digestion.