Hydronephrosis in Horses: Swollen Kidney From Urine Back-Up

Quick Answer
  • Hydronephrosis means a kidney becomes stretched and swollen because urine cannot drain normally into the bladder.
  • In horses, it is usually linked to a blockage somewhere in the upper urinary tract, such as a ureteral stone, scarring, a congenital abnormality, or less commonly a mass.
  • Signs can be vague at first. Some horses show colic-like discomfort, weight loss, poor appetite, blood in the urine, straining to urinate, or reduced performance.
  • Diagnosis usually requires your vet to combine an exam with bloodwork, urinalysis, and ultrasound. Some horses also need endoscopy or contrast imaging.
  • Prompt veterinary care matters because long-term pressure can permanently damage the affected kidney, and some horses already have kidney compromise by the time the problem is found.
Estimated cost: $450–$3,500

What Is Hydronephrosis in Horses?

Hydronephrosis is swelling of the kidney caused by urine back-up. Instead of flowing normally from the kidney through the ureter to the bladder, urine meets resistance or a blockage. Pressure builds inside the kidney, stretching the renal pelvis and surrounding tissue. Over time, that pressure can thin and damage the kidney itself. (petmd.com)

In horses, hydronephrosis is considered uncommon, but it is clinically important because signs may be subtle until damage is already present. It may affect one kidney or, less commonly, involve both sides if there is more widespread urinary outflow disease. Horses can sometimes compensate surprisingly well when only one kidney is affected, which is one reason the condition may be discovered late. (aaep.org)

Hydronephrosis is not a final diagnosis by itself. It is a description of what has happened to the kidney because something else is interfering with urine flow. Your vet's job is to identify that underlying cause, assess how much kidney function remains, and help you choose a treatment path that fits your horse's condition and your goals. (merckvetmanual.com)

Symptoms of Hydronephrosis in Horses

  • Mild, recurring colic-like discomfort
  • Blood in the urine, especially after exercise
  • Straining to urinate or frequent attempts to urinate
  • Dribbling urine or reduced urine output
  • Poor appetite, weight loss, or dull attitude
  • Fever
  • Back, flank, or abdominal pain on examination
  • Lethargy, dehydration, or signs of kidney failure

Some horses with hydronephrosis have obvious urinary signs, but others do not. In equine urinary stone disease, signs can include dysuria, pollakiuria, hematuria, urine dribbling, and colic. Horses with ureteral stones may already have meaningful kidney damage before the problem is recognized. (merckvetmanual.com)

See your vet immediately if your horse is repeatedly straining to urinate, producing very little urine, showing moderate to severe colic signs, has a fever, or seems suddenly weak or depressed. Those findings can point to obstruction, infection, or kidney injury and should not be monitored at home without veterinary guidance. (merckvetmanual.com)

What Causes Hydronephrosis in Horses?

The most important cause is obstruction of urine flow. In horses, that may happen because of a ureteral stone, a kidney stone that has moved, inflammatory debris, scarring or narrowing of the ureter, or a congenital urinary tract abnormality. Equine references note that ureteral stones can be partially obstructive on both sides and may not be recognized until kidney values rise or imaging shows damage. (merckvetmanual.com)

Infection can also play a role. Ascending or descending urinary tract infection may inflame tissues, contribute to debris, and worsen drainage. In foals and younger horses, developmental abnormalities of the urinary tract are another consideration. Less commonly, external compression from a mass or severe surrounding disease can interfere with the ureter and lead to urine back-up. (petmd.com)

Because hydronephrosis is a consequence rather than a single disease, your vet will usually think through several categories at once: stone disease, infection, congenital change, trauma, and mass effect. That broader approach helps avoid missing a treatable cause. (merckvetmanual.com)

How Is Hydronephrosis in Horses Diagnosed?

Diagnosis starts with a full history and physical exam, including attention to urination habits, colic episodes, appetite, weight change, and exercise-related blood in the urine. Your vet may perform a rectal exam to assess the bladder and nearby structures, although upper urinary tract disease often needs imaging to be confirmed. Bloodwork helps evaluate kidney values, hydration, inflammation, and electrolyte changes, while urinalysis can look for blood, crystals, infection, and concentration problems. (merckvetmanual.com)

Ultrasound is one of the most useful tests in horses. Merck's equine emergency imaging guidance specifically notes that the kidney should be evaluated for nephrolithiasis, hydronephrosis, and abnormal architecture. Ultrasound can show an enlarged renal pelvis, changes in kidney shape, and sometimes the obstructing stone or secondary damage. (merckvetmanual.com)

If the case is complicated, your vet may recommend referral for cystoscopy, catheter-based evaluation, contrast studies, or repeat imaging over time. That is especially helpful when the obstruction is not clearly visible, when surgery is being considered, or when your vet needs to estimate how much function the affected kidney still has. (aaep.org)

Treatment Options for Hydronephrosis in Horses

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Budget-Conscious Care

$450–$1,500
Best for: Horses that are stable, have mild signs, or need an initial stepwise workup before a referral decision.
  • Farm call or clinic exam
  • Basic bloodwork and urinalysis
  • Focused ultrasound if available
  • Pain control and fluid support as directed by your vet
  • Monitoring urine output, appetite, hydration, and kidney values
  • Referral discussion if obstruction is suspected but cannot be relieved in the field
Expected outcome: Variable. Some horses remain stable if the problem is partial or chronic, but prognosis worsens if there is ongoing obstruction or progressive kidney damage.
Consider: This approach can identify a likely problem and support the horse, but it may not fully define the cause or remove the obstruction. Delays can matter if urine flow is significantly blocked.
Most Common

Recommended Standard Treatment

$1,500–$4,500
Best for: Most horses with confirmed or strongly suspected hydronephrosis that are painful, dehydrated, azotemic, or not improving with outpatient care.
  • Complete exam with CBC, chemistry panel, and urinalysis
  • Detailed abdominal and urinary tract ultrasound
  • Hospitalization for IV fluids and monitoring when needed
  • Targeted antimicrobial therapy if infection is documented or strongly suspected
  • Repeat kidney value checks and serial imaging
  • Referral consultation for endoscopy or surgical planning if a stone or ureteral blockage is likely
Expected outcome: Fair to guarded, depending on whether one or both kidneys are involved, how long the obstruction has been present, and whether the cause can be corrected.
Consider: Provides a more complete picture and safer monitoring, but still may not resolve a fixed obstruction without advanced procedures.

Advanced / Critical Care

$4,500–$10,000
Best for: Horses with severe obstruction, worsening kidney values, persistent pain, recurrent urinary signs, or cases where a procedure may preserve comfort or function.
  • Referral hospital care with advanced imaging or endoscopy
  • Contrast studies or specialized urinary tract evaluation
  • Intensive fluid therapy and electrolyte management
  • Surgical or interventional management when feasible for obstructive stones or severe unilateral disease
  • Management of complications such as infection, severe pain, or kidney failure
  • Post-procedure monitoring and repeat imaging
Expected outcome: Guarded overall, but some horses do well when the obstruction is unilateral and the opposite kidney is healthy enough to compensate.
Consider: This tier offers the most diagnostic and treatment options, but it requires referral-level resources, transport, and a higher cost range. Not every horse is a candidate for intervention.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Hydronephrosis in Horses

Bring these questions to your vet appointment to get the most out of your visit.

  1. Do you think this is a true obstruction, or could infection or inflammation be causing the kidney swelling?
  2. Is one kidney affected or both, and how much function do you think the other kidney has?
  3. What did the ultrasound show about the renal pelvis, ureter, and bladder?
  4. Which blood and urine changes matter most in my horse's case right now?
  5. Does my horse need hospitalization, or is monitored outpatient care reasonable today?
  6. Are there signs of a stone, congenital abnormality, or mass that make referral more urgent?
  7. What are the realistic conservative, standard, and advanced treatment options for this specific horse?
  8. What changes at home would mean I should call immediately or bring my horse back in?

How to Prevent Hydronephrosis in Horses

Not every case can be prevented, especially when a horse has a congenital urinary tract abnormality or a problem that develops silently over time. Still, early attention to urinary signs can make a real difference. Call your vet sooner rather than later for blood in the urine, repeated straining, urine dribbling, recurring colic, or unexplained weight loss. Those signs may seem mild at first, but they can point to stone disease or another obstructive process. (merckvetmanual.com)

Good hydration and routine health monitoring are practical preventive steps. Horses with a history of urinary tract disease may benefit from periodic urinalysis, kidney value checks, and ultrasound rechecks based on your vet's recommendations. Prompt treatment of urinary infections and follow-up after any stone episode may also reduce the chance that ongoing inflammation or recurrent obstruction will go unnoticed. (petmd.com)

Prevention is really about catching the underlying cause before the kidney is under pressure for too long. If your horse has had urinary stones, kidney abnormalities, or unexplained hematuria in the past, ask your vet what monitoring schedule makes sense for your horse's age, workload, and history. (aaep.org)

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