A healthy horse produces roughly 15 to 16 liters (about 4 gallons) of urine per day. If your horse is urinating noticeably more than that, soaking through bedding faster than usual, or spending more time in a urinating posture, something is driving the increase. The causes range from simple dietary factors to serious medical conditions, and figuring out which one applies to your horse starts with understanding what can go wrong.
How to Tell If It’s Actually Excessive
More wet bedding doesn’t always mean more urine. A horse that’s drinking more water will naturally pee more, and the two problems (excessive drinking and excessive urination) are so intertwined that vets treat them as a single investigation. A rough guideline: if your horse is drinking more than 7.5% of its body weight in water daily, increased urination is probable. For a 1,000-pound horse, that’s about 34 liters or 9 gallons a day. If water intake exceeds 10% of body weight, the increase is definite and warrants investigation.
On the output side, urinating more than 3% of body weight daily is considered probable polyuria, and above 5% it’s definitive. In practice, most owners notice the problem through stall conditions, not by measuring urine volume directly. Consistently soaked bedding, a strong ammonia smell, or a horse that seems to urinate far more frequently than its pasture mates are all reasonable reasons to look deeper.
Diet Can Be the Simplest Explanation
High-protein feeds, especially alfalfa hay or alfalfa-based haylage, are a common and often overlooked cause. Alfalfa contains roughly 130 to 140 grams of crude protein per kilogram of dry matter, compared to about 80 to 88 grams in meadow hay. When a horse takes in more protein than it needs, the body breaks the excess down into urea, which the kidneys must flush out with water. Studies comparing horses on alfalfa versus meadow hay show notably higher blood urea levels in the alfalfa-fed groups within just three weeks.
Alfalfa is also high in calcium, and horses excrete a much higher percentage of calcium through their kidneys than most other species. That extra calcium load means more water pulled into the urine. If your horse recently switched to alfalfa or a higher-protein concentrate, the diet change alone could explain the increase. Cutting back on protein and monitoring water intake for a week or two is a reasonable first step before pursuing diagnostics.
Salt and electrolyte supplements can also bump up water intake and urine output. This is usually harmless and self-limiting, but if your horse has free-choice access to a salt block and seems to be using it heavily, it’s worth noting for your vet.
Cushing’s Disease (PPID)
Pituitary pars intermedia dysfunction, commonly called Cushing’s disease, is one of the most frequent medical causes of excessive urination in older horses. The condition involves an enlarging part of the pituitary gland at the base of the brain, and the increased urination likely results from several overlapping mechanisms. The expanding tissue can interfere with the production of hormones that tell the kidneys to conserve water, essentially creating a form of diabetes insipidus. In some horses, elevated cortisol-like hormones or sugar spilling into the urine may also play a role, though these are less common in PPID than in other species.
Other signs that point toward PPID include a long, curly coat that doesn’t shed normally, muscle wasting along the topline, a pot-bellied appearance, recurrent laminitis, and slow wound healing. The condition is most common in horses over 15 years old. A blood test measuring a hormone called ACTH is the standard screening tool. PPID is manageable with daily medication, and many horses respond well, with water intake and urination returning closer to normal.
Kidney Disease
Chronic kidney disease gradually erodes the kidneys’ ability to concentrate urine. In the early stages, a horse may produce large volumes of dilute urine before any other signs appear. As the disease progresses, toxins that the kidneys normally filter out begin accumulating in the blood, a state called azotemia. Weight loss, poor appetite, and a rough coat often follow.
Vets screen for kidney disease with a basic blood panel. The key marker is creatinine, a waste product from muscle metabolism. In horses, a creatinine level above 2.0 mg/dL lasting longer than three months defines chronic kidney disease. Blood urea nitrogen is checked alongside creatinine, and urine tests (specific gravity, protein levels, electrolyte ratios) help gauge how much function remains. Early detection matters because dietary adjustments and supportive care can slow progression, even though the damage itself isn’t reversible.
Psychogenic Polydipsia
Some horses simply drink too much water out of habit or boredom, a behavioral condition called psychogenic polydipsia. The kidneys are perfectly healthy, but they’re overwhelmed by the sheer volume of fluid coming in and respond by producing large amounts of very dilute urine. This is considered one of the more common causes alongside PPID and kidney disease.
The telltale sign is a urine specific gravity below 1.008, meaning the urine is extremely dilute, almost like water. Distinguishing psychogenic polydipsia from diabetes insipidus (where the brain fails to produce enough of the hormone that signals the kidneys to retain water) requires a modified water deprivation test. Under veterinary supervision, water intake is gradually restricted over three to four days. If the urine concentrates above a specific gravity of 1.020 during the restriction, the kidneys can do their job and the problem is behavioral. If the urine stays dilute despite water restriction, the kidneys or the hormonal signaling pathway has a problem that needs further workup.
Horses with psychogenic polydipsia often improve with environmental changes: more turnout, social interaction, or removing the constant availability of water in favor of offering it at regular intervals. This should only be attempted after a vet has confirmed the diagnosis, since restricting water in a horse with kidney disease or diabetes insipidus can be dangerous.
Medications and Supplements
Corticosteroids are the most commonly implicated medications. Dexamethasone, frequently used in horses for inflammation and allergic reactions, is well documented to cause increased thirst and urination. The effect is usually temporary, resolving once the medication course ends. If your horse started peeing more shortly after receiving a steroid injection or starting an oral steroid, the timing is likely not a coincidence.
Some herbal supplements and certain feeds with added molasses can also increase water intake. Reviewing any recent changes to your horse’s medication or supplement regimen is a useful part of the puzzle.
Less Common Causes
Diabetes mellitus, while common in dogs and cats, is rare in horses. When it does occur, excess sugar spills into the urine and drags water with it, producing the classic combination of excessive thirst, excessive urination, and weight loss despite a good appetite. A simple blood glucose test can rule this in or out quickly.
Elevated blood calcium (hypercalcemia), sometimes caused by certain tumors or vitamin D toxicity, forces the kidneys to excrete the excess mineral along with large volumes of water. This is uncommon but straightforward to detect on a standard blood panel.
What Your Vet Will Want to Know
Before the appointment, tracking a few details will help your vet narrow things down faster. Note how much water your horse is drinking daily if possible (mark the level on a bucket morning and evening). Pay attention to how frequently the horse urinates and whether the urine looks unusually clear or pale. Write down any recent diet changes, new supplements, medications, or changes in turnout and stall routine. Mention the horse’s age, since PPID is far more likely in an older horse, while psychogenic polydipsia can occur at any age.
The initial workup is straightforward: a blood panel checking creatinine, urea, glucose, calcium, and ACTH levels, plus a urine sample to measure specific gravity and look for protein or glucose. These results together can identify or rule out the most common causes in a single visit, pointing toward the right next step whether that’s a diet adjustment, medication, or further testing.