Horses with kidney problems need a diet that reduces the workload on their kidneys while still providing enough energy and nutrients to maintain body condition. The core strategy centers on three things: switching to low-calcium forage, ensuring constant access to fresh water, and being careful with salt, protein, and certain supplements. The specifics depend on whether your horse has acute or chronic kidney disease and what blood work reveals, but the dietary principles below apply broadly.
Why Forage Choice Matters Most
The single most important dietary change for most horses with kidney disease is switching from alfalfa or other legume hays to grass hay. Horses are uniquely prone to high blood calcium levels, and this is directly diet-dependent. According to a European College of Equine Internal Medicine (ECEIM) consensus statement, elevated calcium can return to normal within days of switching from legume hay to grass hay.
Timothy, orchard grass, bermuda, and other grass hays are all good choices because they’re naturally lower in calcium and protein than legumes. Alfalfa and clover hays pack significantly more calcium per pound, which is a problem because damaged kidneys struggle to regulate calcium. Excess calcium in the blood can lead to further mineral deposits in kidney tissue, worsening the damage.
Quality pasture is also an excellent option when available. Fresh grass provides omega-3 fatty acids and vitamin E naturally, both of which have been shown to slow the progression of chronic kidney disease in humans and small animals. The evidence in horses specifically is still limited, but pasture turnout has the added benefit of encouraging movement and water intake from the grass itself.
Keeping Your Horse Hydrated
Water intake is critical. Dehydration is one of the fastest ways to push compromised kidneys toward failure, and many kidney problems in horses develop or worsen during periods of inadequate hydration. Horses with stable chronic kidney disease need constant, unrestricted access to clean, fresh water. In cold weather, offering lukewarm water can encourage drinking, since some horses reduce their intake when water is near freezing.
Soaking hay before feeding is a practical way to increase water consumption without your horse even noticing. You can also add water to any bucket feeds to create a soupy mash. Monitoring urine output and bedding wetness gives you a rough daily gauge. If your horse’s bedding stays unusually dry for 12 to 18 hours, that’s a red flag for inadequate urine production and warrants immediate veterinary attention.
Providing Energy Without Overloading the Kidneys
Horses with kidney problems often lose weight because their appetite drops or because owners cut back on feed without replacing the lost calories. Fat is the best tool for maintaining energy intake in these horses. Vegetable oils provide roughly 2.25 times more energy per pound than carbohydrates, and they add no extra protein or minerals that the kidneys would need to process.
Corn oil, soybean oil, or canola oil can be top-dressed on a small amount of a low-protein, low-calcium carrier feed. Start with a quarter cup per day and gradually work up to one to two cups, depending on your horse’s size and caloric needs. Rice bran (15 to 18% fat) and ground flax seeds (30 to 40% fat) are other options, though rice bran does contain phosphorus, so it should be used cautiously and ideally after discussing it with your vet.
If your horse needs grain, choose a simple, low-protein option like plain oats or a commercial senior feed designed to be low in protein and minerals. Avoid high-protein commercial feeds, sweet feeds with molasses, and anything fortified with extra vitamins and minerals unless you’ve confirmed the specific nutrient profile is appropriate.
Salt, Minerals, and Supplements to Watch
Salt supplementation is a common recommendation for healthy horses, but it requires caution in horses with kidney disease. The ECEIM consensus does not recommend adding salt beyond what’s already in the normal diet. Extra salt can worsen edema and high blood pressure, both of which are complications of kidney dysfunction. If your horse already has swelling in the legs or sheath, a restricted-salt diet is specifically recommended.
Vitamin D supplementation should be avoided entirely. Horses with kidney problems are at risk for calcium buildup and kidney mineralization, and vitamin D promotes calcium absorption. Toxicity has been documented in horses fed grain diets high in cholecalciferol (the form of vitamin D found in many supplements and fortified feeds). Check the labels on any commercial feed or supplement your horse currently receives and remove anything containing added vitamin D.
Omega-3 fatty acid supplements and vitamin E are worth discussing with your vet. Both slow kidney disease progression in other species, and while hard evidence in horses is lacking, they carry minimal risk. Quality pasture provides both naturally. If your horse doesn’t have pasture access, a vitamin E supplement and a small amount of flax oil could fill that gap without adding problematic minerals.
What to Avoid Entirely
- Alfalfa and clover hay: Too high in calcium and protein for most horses with kidney disease.
- Extra salt blocks or electrolyte pastes: Can worsen fluid retention and blood pressure issues.
- Vitamin D supplements or heavily fortified feeds: Risk of worsening calcium deposits in kidney tissue.
- High-protein feeds: Protein breakdown creates nitrogenous waste that kidneys must filter. Reducing protein intake lowers that burden.
- NSAIDs like phenylbutazone (bute): These are not a feed item, but they deserve mention because many horse owners give bute casually for soreness. NSAIDs can cause kidney failure on their own, especially in a horse that’s already dehydrated or has reduced kidney function.
Monitoring Whether the Diet Is Working
Your vet will track kidney function through blood work, primarily looking at creatinine levels and blood urea nitrogen (BUN). Creatinine reflects how well the kidneys are filtering waste, and BUN rises when protein breakdown products accumulate. After a diet change, these values should stabilize or improve within a few weeks if the kidneys still have enough functional tissue remaining. Calcium levels are also monitored closely, and the ECEIM consensus notes that switching to grass hay alone can normalize high calcium within days.
At home, the things to watch are appetite, water intake, urination patterns, weight, and energy level. A horse that’s eating well, drinking steadily, urinating normally, and holding its weight is responding to the dietary changes. Weight loss, increased lethargy, a drop in appetite, or visible swelling in the legs or underbelly all signal that the current plan needs adjustment. Keeping a simple daily log of how much hay and water your horse goes through makes it much easier to catch subtle changes before they become emergencies.