Acute Kidney Injury in Horses: Signs, Causes, and Emergency Care

Acute kidney injury, often shortened to AKI, is a sudden drop in kidney function. The kidneys normally remove waste products, help regulate water balance, and keep electrolytes and acid-base levels in a safe range. When they are injured, waste builds up in the bloodstream and the horse may become dehydrated, weak, acidotic, or unable to make normal amounts of urine.

In horses, AKI is often a secondary problem rather than a disease that starts in the kidneys alone. It may develop after severe dehydration, colitis, endotoxemia, blood loss, anesthesia, shock, or exposure to medications that can stress the kidneys. Merck notes that acute kidney disease in horses can follow severe dehydration, bleeding, systemic infection, and general anesthesia, and that your vet may detect kidney dysfunction on bloodwork before obvious outward signs appear.

Some horses show vague early signs, such as poor appetite, dullness, weight loss over a short period, or reduced thirst. Others become clearly ill, with worsening dehydration, swelling, abnormal urination, or signs tied to the original problem, like diarrhea or colic. Because the early signs can be subtle, pet parents may not realize the kidneys are involved until the horse is already quite sick.

This is why AKI should be treated as an emergency. Fast veterinary care gives your horse the best chance of stabilizing the underlying illness, protecting the kidneys from further damage, and supporting recovery before the injury becomes irreversible.

Acute kidney injury in horses usually happens when the kidneys receive too little blood flow or are exposed to something that directly damages kidney tissue. Common low-blood-flow causes include severe dehydration, shock, hemorrhage, endotoxemia, sepsis, and low blood pressure during or after anesthesia. Horses with colitis or other serious gastrointestinal disease are at particular risk because they can lose large amounts of fluid quickly.

Medication-related injury is another major cause. NSAIDs used in horses, including flunixin and phenylbutazone, can contribute to kidney damage when doses are too high, treatment lasts too long, or the horse is already dehydrated or systemically ill. Aminoglycoside antibiotics, especially gentamicin and amikacin, are also well known for nephrotoxic potential and require careful dosing and monitoring.

Less common causes include toxins, pigment injury from severe muscle breakdown, and urinary tract or kidney infections. In some cases, more than one factor is involved. For example, a horse with diarrhea may be dehydrated, receive NSAIDs for pain, and then develop worsening kidney perfusion and tubular injury.

Your vet will focus on both the kidneys and the trigger behind them. That matters because successful treatment depends on correcting the underlying problem while avoiding any further kidney stress.

Diagnosis starts with a careful history and physical exam. Your vet will want to know about recent colic, diarrhea, fever, transport stress, anesthesia, blood loss, dehydration, and any medications your horse has received. Blood and urine testing are the core first steps. Merck notes that urinary tract disorders in horses are commonly diagnosed using history, physical examination, and blood and urine tests.

Bloodwork often includes creatinine, BUN, electrolytes, total protein, and acid-base assessment. Rising creatinine is a key marker, but your vet interprets it in context because body condition, hydration status, and timing matter. Urinalysis helps assess urine concentration, protein, blood, sediment, and other changes that may point toward tubular injury or infection.

Many horses also benefit from ultrasound of the kidneys and urinary tract. Imaging can help your vet look for kidney enlargement or changes in echogenicity, urinary obstruction, or evidence of chronic disease that may change the outlook. In more complex cases, your vet may recommend repeated bloodwork over 24 to 72 hours to track whether values are improving, stable, or worsening.

Because AKI can overlap with prerenal dehydration or chronic kidney disease, diagnosis is often about putting several pieces together. That is one reason early veterinary evaluation matters so much. A horse may look only mildly ill at first, while the lab changes tell a more serious story.

Not every case can be prevented, but many can be risk-reduced. The biggest steps are maintaining hydration, responding quickly to diarrhea or colitis, and using medications carefully. Horses that are sick, dehydrated, febrile, or off feed are more vulnerable to kidney injury, especially if they also receive NSAIDs or aminoglycoside antibiotics.

Work closely with your vet before giving repeated doses of phenylbutazone, flunixin, or other potentially nephrotoxic drugs. Follow the prescribed dose and schedule exactly, and do not combine medications unless your vet specifically recommends it. If your horse is hospitalized, ask how kidney values will be monitored when higher-risk drugs or anesthesia are involved.

Routine wellness bloodwork can also help identify horses that may already have reduced kidney reserve before a stressful event. That is especially useful in older horses, horses with a history of severe illness, or horses that may need repeated anti-inflammatory treatment. Early recognition of dehydration, reduced appetite, or changes in urination can make a meaningful difference.

Practical prevention is about timing. Prompt veterinary care for colic, diarrhea, fever, toxic exposures, and post-anesthetic complications gives your horse the best chance of avoiding secondary kidney damage.