How Horses Process Protein — And Why Too Much Can Cause Trouble

Protein is essential for every horse. It builds muscle, supports recovery, fuels the immune system, and keeps the body functioning well. But like so many things in equine nutrition, balance matters. When protein intake climbs higher than the horse can comfortably use, the body has to work overtime to deal with the excess, and that’s where problems begin. Protein digestion starts in the stomach with pepsin and gastric acid, then continues in the small intestine where enzymes break proteins down into amino acids. These amino acids are absorbed into the bloodstream and sent to the liver for processing. As the liver metabolizes them, it produces nitrogenous waste, mainly ammonia, urea, and uric acid. In normal amounts, the body handles these easily, but when protein intake is too high, these waste products accumulate and become irritating or even toxic. The liver and kidneys work harder to clear the excess, which can lead to dehydration, electrolyte loss, skin irritation, and even joint inflammation. A dull coat, itchiness, strong‑smelling urine, stiffness, or low energy are often early signs that the protein load is simply too much.

This is why hay testing is so important. It’s the only way to know whether your horse actually needs extra protein in the first place. What I often see is owners adding alfalfa or protein supplements “just in case,” without knowing how much protein their horse is already getting, or how much they truly need. Horses are not humans, and we cannot feed them like humans. I see this often: people assume that because humans benefit from added protein, their horses will too. But horses are herbivores with a completely different digestive system, different metabolic pathways, and different requirements. What works for us does not automatically translate to them.

Another pattern I see is horses receiving excess protein while also dealing with ulcers or gut irritation. Alfalfa can be helpful in certain cases, but it’s not always the right choice, especially when a horse is on omeprazole. Omeprazole reduces stomach acid, and stomach acid is essential for protein digestion. When acid is suppressed, protein isn’t broken down efficiently, which can create a cascade of digestive challenges and systemic stress. I’ll be diving deeper into this in another blog, because it’s a big topic and one that affects many horses.

It’s also important to remember that not all protein sources are equal. Some proteins are harder for horses to digest and can place unnecessary strain and toxic load on the digestive system. These include things like soybean meal, canola meal, whey protein, pea protein, fish meal, and low‑quality amino acid blends to name a few. They are often not ideal for horses for many reasons, including digestibility, inflammatory potential, and how they interact with the equine gut.

For most horses, the foundation should be a good‑quality hay source with appropriate protein levels and access to as many different live plants as possible. If additional protein is needed, options like alfalfa hay, pellets, or cubes can be helpful, but only when the horse responds well and the diet actually calls for it. When the base forage is balanced, many horses don’t require extra protein supplements at all.

Protein is important but more is not always better. When we understand how the horse processes it, choose protein sources intentionally, and remember that horses are not humans, we can support the whole body instead of overwhelming it. A balanced diet is one of the most powerful tools we have for keeping horses healthy, comfortable, and thriving.