What Your Horse’s Urine Is Telling You: [Urinary Symptom Guide]

A properly functioning urinary system plays a vital role in maintaining the overall health and well-being of a horse. It acts as a filter, removing waste and toxins from the bloodstream and preventing harmful substances from accumulating in the body. ^[1]

Like all internal organs and their related structures, the urinary system in horses is at risk of developing various conditions that can disrupt its normal function. These conditions and diseases range from infections and inflammation to structural abnormalities and metabolic disturbances.

It’s important for horse owners to familiarize themselves with the hallmark signs of urinary dysfunction. Signs include frequent urination, blood in the urine, straining to urinate, increased thirst, and pain or discomfort when urinating.

By understanding how urinary changes can signal underlying conditions, owners and caretakers can make informed management decisions and seek veterinary guidance early, ensuring the best chance of a positive health outcome for horses.

The Equine Urinary System

The horse’s urinary system plays a crucial role in maintaining overall health by eliminating waste products and regulating fluid balance.

This system comprises several key components: ^[1][2][3][4]

• Kidneys
• Ureters
• Bladder
• Urethra

Although the urinary system, digestive system, and reproductive system are all found in close proximity to each other within the abdominal and pelvic cavities, it’s important to recognize that they are distinct systems.

While all three systems have orifices and excretions and these may sometimes overlap as health indicators, each system serves unique functions and operates independently.

Equine Urinary System Anatomy

Learning the basics of urinary anatomy is the first step to understanding urinary symptoms. Important anatomy includes: ^[1]

• Kidneys: Positioned on either side of the spine just below the last rib, horses have two kidneys. These organs filter blood, removing waste products and excess metabolites to form urine. Additionally, they regulate electrolyte balance, blood pressure, and red blood cell production by secreting hormones.
• Ureters: Narrow tubes connecting the kidneys to the bladder. Ureters transport urine through peristaltic movements, which are wave-like muscle contractions that propel the urine downward.
• Bladder: A hollow, muscular organ located in the pelvis, the bladder stores urine until it is expelled from the body during urination.
• Urethra: A tube that carries urine from the bladder to the outside of the body, the urethra allows for the elimination of urine from the urinary tract. The urethra is significantly longer in males than it is in females, as it runs the entire length of the penis. In males, the urethra also excretes semen, which is produced in the testicles.

Illustration: Dr. Ana Mesa, PhD

Urine Production and Excretion

Urine production begins as blood enters the kidneys through the renal arteries. The functional substructure of the kidneys is called the nephron. Each kidney contains hundreds of thousands of nephrons, which is where blood filtration takes place.

Each nephron starts at the glomerulus, a bundle of small capillaries that prevents the excretion of large, useful components of the blood, such as proteins. The fluid that leaves the glomerulus contains small blood components, such as electrolytes. This fluid enters the renal tubules, where wastes and excess metabolites are deposited and sorted. Essential nutrients, water, and electrolytes are reabsorbed into the bloodstream, while the waste products are converted into urine.

The renal tubules deliver urine into the collecting ducts, which drain into the ureters. The ureters transport the urine to the bladder where it is stored until the horse urinates.

Healthy horse urine should be a yellowish or tan hue, indicating proper hydration and normal kidney function. Typically, horses urinate between 7 and 10 times per day. ^[5]

Equine Urinary Symptoms

Monitoring your horse’s urinary habits and noting changes can help identify underlying health issues early. Changes in urination frequency or behavior can indicate a urinary disorder.

Follow this guide to learn about symptoms to watch for and their significance, so you can proactively address any potential health concerns.

Excessive Thirst and Urine Output: Polyuria & Polydipsia

Polyuria in horses refers to excessive production of urine, defined as output higher than 50 mL / kg (0.8 oz / lb) body weight per day for an adult horse. Polyuria is not a disease itself but a symptom that may indicate various underlying conditions. ^[6][7]

Polydipsia refers to excessive thirst and increased water consumption beyond normal levels, which often accompanies polyuria. This instinctive behavior helps the horse avoid dehydration. ^[6][7]

Frequent Urination: Pollakiuria

Pollakiuria and polyuria may appear similar, but they are distinct symptoms that describe abnormal urination, each referring to different aspects of physiological dysfunction. ^[8]

Pollakiuria describes abnormally frequent urination or the need to urinate more often than usual. This is different than polyuria, which is characterized by urinating large volumes of fluid.

Pollakiuria typically manifests as the urge to urinate frequently in small amounts or as a persistent feeling of needing to urinate. ^[8]

Blood in Urine: Hematuria, Myoglobinuria, and Hemoglobinuria

Brown, pink, or red urine usually indicates the presence of blood or components of blood in the urine. Biochemically, there are three subtypes of bloody urine which can be identified with urinalysis.

The three types of bloody urine refer to which component of blood is detected: ^[9][10]

• Hematuria refers to the presence of whole red blood cells
• Myoglobinuria refers to the presence of myoglobin, the protein that stores oxygen in the muscles
• Hemoglobinuria refers to the presence of hemoglobin, the protein that transports oxygen in the blood

Identifying which component of blood is in the urine helps veterinarians locate the source of the bleeding. For example, hematuria results from hemorrhage or bleeding into the urinary tract, such as from injury, infection, or urinary stones. ^[11]

Myoglobinuria occurs when there is excessive muscle breakdown, such as during rhabdomyolysis (tying-up). The components of muscle breakdown, including myoglobin, are filtered by the kidneys and end up in the urine. ^[11]

Hemoglobinuria occurs when there is hemolysis, or the destruction of red blood cells in the body. For example, red maple poisoning is a condition that results in hemoglobinuria. ^[11]

Common causes of bloody urine in horses include: ^[2]

• Urinary tract infections
• Bladder or kidney stones
• Injuries
• Inflammation of the urinary bladder or urethra
• Urinary or kidney tumors
• Equine infectious anemia
• Leptospirosis

Painful Urination: Dysuria

Dysuria in horses is characterized by difficulty or pain during urination. It is a symptom that can indicate various underlying issues in the urinary tract.

Horses with dysuria may: ^[10]

• Strain while trying to urinate
• Frequently attempt to urinate, often unsuccessfully
• Attempt to urinate with an unusual posture, such as stretching out or arching the back
• Indicate pain and discomfort (restlessness, pawing, kicking at the abdomen, etc.)
• Have reduced urine flow

Urinary System Conditions

The horse’s urinary system is vulnerable to various diseases and conditions, which often have similar symptoms. Urinary conditions can be broadly categorized as infectious diseases, non-infectious diseases, or congenital abnormalities.

Noninfectious Diseases

Some of the conditions associated with urinary system symptoms are related to genetics, lifestyle, management, and other predisposing risk factors that are not contagious.

Kidney Disease & Failure

Chronic kidney disease (CKD), or chronic renal failure, is a rare and progressive condition characterized by gradual loss of kidney function over time. In horses, CKD may occur as a result of aging, genetic predisposition, long-term exposure to toxins, certain medications and underlying health conditions. ^[7][12]

The clinical signs of CKD in horses can be subtle and may not become apparent until the disease is advanced. Common symptoms of CKD include: ^[7][12]

• Increased thirst and urination (polydipsia and polyuria)
• Ventral edema (accumulation of fluid under the skin of the belly)
• Weight loss
• Decreased appetite
• Lethargy
• Poor coat condition

Overview of CKD in horses: ^[7][12]

• Age predisposition: Older horses
• Sex predisposition: None
• Diagnosis: X-ray, ultrasound, urinalysis, bloodwork
• Treatment: Treating the underlying cause. If kidney failure has occurred, supportive treatment is warranted.
• Prognosis: Poor

Urinary Stones (Calculi)

Urinary stones, (also referred to as calculi and uroliths), are mineral deposits that form in the urinary tract. In horses, these stones most commonly develop in the bladder. The prevalence of calculi in horses is low, occurring in 0.04% to 0.5% of cases seen in equine clinics. ^[13]

Common symptoms of uroliths in horses include: ^[14]

• Difficulty urinating
• Frequent attempts to urinate (pollakiuria)
• Blood in the urine
• Recurrent bouts of mild colic

Overview of uroliths in horses: ^[14]

• Age predisposition: Older horses
• Sex predisposition: None
• Diagnosis: Urinalysis, symptoms
• Treatment: Surgical removal (cystotomy)
• Prognosis: Good following treatment, but recurrence is common

Uroperitoneum in Foals

Uroperitoneum in foals refers to the abnormal accumulation of urine in the peritoneal cavity, which is the space within the abdomen. This condition typically occurs due to a rupture or tear in the urinary tract. This allows urine to leak into the abdomen instead of being expelled through the normal channels. ^{[12][15] [16]}

Common clinical signs of uroperitoneum include: ^{[12][15] [16]}

• Lethargy
• Diarrhea
• Weakness
• Tachycardia (rapid heart rate)
• Tachypnea (rapid breathing)
• Abdominal distension
• Urine dribbling
• Colic

Overview of uroperitoneum in horses: ^{[12][15] [16]}

• Age predisposition: Foals (Under 1 year)
• Sex predisposition: None
• Diagnosis: Abdominal ultrasound and/or abdominocentesis
• Treatment: Surgery
• Prognosis: Very good in uncomplicated cases

Kidney Tumours (Renal Neoplasia)

Primary renal neoplasia, usually renal cell carcinoma (RCC), is a rare type of kidney tumor. It is the most common primary renal tumor in horses, originating from the epithelial cells of the renal tubules. RCC is significant due to its malignant and aggressive nature, often resulting in a poor prognosis. ^[17][18][19]

RCC typically affects one kidney, and initial clinical signs are vague. Signs like abdominal pain, blood in the urine, and the detection of abdominal masses usually do not appear until late in the disease process, making early detection challenging. ^[17][18]

Common clinical signs include: ^[17][18]

• Weight loss
• Colic
• Blood in urine (late stage)

Overview of renal cell carcinoma in horses: ^[17][18]

• Age predisposition: None
• Sex predisposition: None
• Diagnosis: Transabdominal ultrasound
• Treatment: Full or partial removal of the kidney (nephrectomy). Supportive treatment is warranted in advanced cases.
• Prognosis: Good with successful nephrectomy. Poor in advanced cases.

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Bladder Tumors

Bladder tumors are exceptionally uncommon in horses, with squamous cell carcinoma (SCC) being the most frequently reported type. This particular tumor arises from the squamous epithelial cells lining the bladder. ^[18][20][21]

The clinical signs associated with bladder tumors closely resemble those of urinary bladder calculi, which underscores the importance of prompt veterinary investigation when symptoms are noted. ^[21]

Common clinical signs include: ^[21]

• Blood in urine
• Abdominal pain (colic)

Overview of bladder tumors in horses: ^[21]

• Age predisposition: None
• Sex predisposition: None
• Diagnosis: Transrectal ultrasound, rectal palpation, cystoscopy
• Treatment: None
• Prognosis: Poor

Infectious Diseases

The urinary system is also vulnerable to contagious diseases, which may be the result of widespread infection or direct exposure to pathogens via the urinary orifice at the end of the urethra.

Urinary Tract Infection (UTI)

A urinary tract infection (UTI) is a bacterial infection that can affect any part of a horse’s urinary system, including the bladder, urethra, and kidneys. These infections are typically ascending infections, where bacteria enters the urethra, initiating an infection in the lower urinary tract before spreading upward. ^[21]

UTIs are rare in healthy horses, but several factors can predispose a horse to infection. Senior horses and those with weakened immune systems are more likely to develop a UTI, as are horses with poor urine flow and the inability to completely empty the bladder during urination. ^[12]

Bacterial urethritis occurs when the urethra becomes infected, while cystitis refers to an infection of the bladder. If bacteria ascend into the kidneys, it can lead to pyelonephritis, a severe kidney infection. This condition can progress to widespread full-body illness and requires prompt veterinary intervention. ^[12]

Common symptoms of equine UTIs include: ^[12]

• Frequent urination (pollakiuria)
• Straining to urinate
• Discolored or bloody urine
• Discomfort or pain during urination

If kidney infection is present, horses may exhibit: ^[12]

• Fever
• Lethargy
• Weakness
• Weight loss
• Loss of appetite

Overview of UTIs in horses: ^[12]

• Age predisposition: None
• Sex predisposition: Mares
• Diagnosis: Urinalysis
• Treatment: Antibiotics and treating any underlying causes
• Prognosis: Generally good, depending on the severity of the infection.

Interstitial Nephritis

Interstitial nephritis describes inflammation of the interstitial tissue surrounding the kidney tubules. This condition can impair kidney function by disrupting the normal structure and function of the kidneys. It is typically caused by a bacterial infection. ^[12]

Common symptoms of interstitial nephritis include: ^[12]

• Frequent urination (pollakiuria)
• Straining to urinate
• Discolored or bloody urine
• Discomfort or pain during urination.

If kidney infection is present, horses may exhibit: ^[12]

• Fever
• Lethargy
• Weakness
• Weight loss
• Loss of appetite

Overview of interstitial nephritis in horses: ^[12]

• Age predisposition: None
• Sex predisposition: None
• Diagnosis: Urinalysis
• Treatment: Antibiotics. If kidney failure has occurred, supportive treatment is warranted.
• Prognosis: Variable

Leptospirosis

Leptospirosis is a bacterial infection caused by Leptospira spp. bacteria. Horses become infected through contact with contaminated water, soil or urine from other infected animals. While clinical signs vary, leptospirosis is associated with abortion and uveitis in horses. ^[12][22]

Foals with leptospirosis are prone to kidney damage, potentially leading to increased thirst, reduced appetite, lethargy, and altered urination. Early detection and treatment are crucial for managing the infection and preventing complications in foals. ^[23][24]

Common symptoms of leptospriosis in horses include ^[23][24]

• Fever
• Yellow eyes or gums (jaundice)
• Recurrent uveitis
• Abortion

Overview of Leptospirosis in horses: ^[23][24]

• Age predisposition: None
• Sex predisposition: None
• Diagnosis: Symptoms, blood work
• Treatment: Antibiotics (oxytetracycline, penicillin, streptomycin, etc.)
• Prognosis: Good in adult horses, poor in young foals

Congenital Abnormalities

Congenital urinary system abnormalities in horses, although rare, are structural or functional defects that are present at birth. These abnormalities occur during fetal development and can affect various structures in the urinary system.

Kidney Abnormalities

Congenital kidney abnormalities in horses are developmental disorders that affect the structure and function of the kidneys from birth. These abnormalities occur during fetal development and can have significant implications for the horse’s health throughout its life.

One congenital abnormality is dysplasia, where the kidney does not form properly before birth. Dysplasia can result in malformed or abnormal kidney tissue, compromising the organ’s ability to function effectively. ^[15]

Another condition is hypoplasia, where the kidneys are underdeveloped or smaller than normal. In cases of hypoplasia, the kidneys may lack sufficient functional tissue to perform their essential roles adequately. ^[15]

These congenital abnormalities can have varying degrees of severity and long-term effects. In mild cases, horses with congenital kidney abnormalities may exhibit few or no clinical signs, while more severe cases can lead to chronic kidney disease or renal failure over time. ^[15]

Common symptoms of congenital kidney defects in horses include: ^[15]

• Weight loss
• Kidney enlargement
• Loss of appetite
• Blood in urine
• Recurrent colic

Polycystic kidney disease (PCKD), while rare in horses, can occur and is usually associated with a hereditary condition. In these cases, fluid-filled cysts of various sizes develop within one or both kidneys, destroying renal tissue and impairing function over time. ^[25]

Overview of PCKD in horses: ^[25]

• Age predisposition: None
• Sex predisposition: None
• Diagnosis: Symptoms, medical history, urinalysis, blood work
• Treatment: No treatment available, supportive treatment is warranted.
• Prognosis: Very poor

Ureter Abnormalities

The most common abnormality of the horse’s urinary system is an ectopic ureter. This congenital condition occurs when one or both ureters do not properly connect to the bladder, instead opening into the urethra, vagina, or another location. ^[26][27]

Symptoms of ectopic ureter in horses include: ^[15]

• Urine dribbling
• Incontinence
• Urine scalding of the skin around the genital area in females (which may lead to vaginitis or vulvitis) or on the belly in males

In horses with a unilateral ectopic ureter (i.e. only occurring in one ureter, not both), normal urination may still occur. Difficulty urinating may be present in bilateral cases where both ureters are ectopic.

Overview of ectopic ureters in horses: ^[26][27]

• Age predisposition: None
• Sex predisposition: Female
• Diagnosis: Endoscopy, ultrasound, excretory pyelogram (X-ray of the urinary tract)
• Treatment: Surgical removal via nephrectomy or redirecting the ureter to connect to the bladder
• Prognosis: Good if no complications follow surgery

Less common ureter abnormalities that can affect urinary function in horses include: ^[26][27]

• Aplasia: the absence or underdevelopment of the ureter
• Duplication: the presence of two ureters for one kidney
• Ureterocele: bulging or swelling at the end of the ureter, typically where it connects to the bladder

Bladder and Urethra Abnormalities

The bladder can be affected by various congenital defects, such as the presence of multiple bladders or abnormalities in the bladder’s development. These anomalies may coincide with other urinary tract abnormalities. ^[28]

Patent urachus is a condition where the urachus, a structure connecting the bladder to the umbilical cord, fails to close after birth. This results in in urine leakage through the umbilicus. Immunocompromised, premature or weak foals are more likely to develop this condition. ^[28][29]

Signs of patent urachus in foals include: ^[28][29]

• Swelling of the umbilicus
• Urine dribbling from the umbilicus
• Urine scalding of surrounding tissue
• Local inflammation
• Urinary tract infections (UTIs)

Overview of patent urachus in foals: ^[28][29]

• Age predisposition: Foals
• Sex predisposition: Male
• Diagnosis: Patient history, clinical signs and x-rays (after a dye is given intravenously)
• Treatment: Surgical treatment (cauterization or cryosurgery), antibiotics
• Prognosis: Good if no complications from surgery

Congenital urethral abnormalities in horses are uncommon, but can include various structural defects that affect the normal function of the urethra, the tube that connects the bladder to the exterior of the body, allowing for the passage of urine.

Overview of Equine Conditions with Urinary Symptoms

Urinary Symptoms and Endocrine Disease

Endocrine disorders, such as pituitary pars intermedia dysfunction (PPID)/Cushing’s and equine metabolic syndrome (EMS), can have significant implications for the health and function of the horse’s urinary system. ^[6]

The kidneys are closely tied to regulation of the hormones involved in thirst and water intake. If these hormonal signaling pathways are disrupted, it can result in changes in thirst and urination.

PPID, characterized by excessive production of cortisol due to dysfunction of the pituitary gland, is commonly associated with urinary issues in horses.

One study suggested that around 31% of PPID horses exhibit polyuria and polydipsia as symptoms, but these may be underreported due to challenges in monitoring water intake and urine output. ^[30]

Increased cortisol triggers excessive thirst and urine production by interfering with antidiuretic hormone, the main hormone that reduces urine production. This increased stimulus to urinate can put strain on the kidneys, increasing the risk of electrolyte imbalances and dehydration.

Supporting Urinary Health

While some conditions related to urinary symptoms are not entirely preventable, horse owners and caretakers can take steps to ensure their equines have excellent kidney and immune health.

Hydration

Adequate water intake helps prevent dehydration, which can lead to concentrated urine and increase the risk of urinary tract infections (UTIs) and kidney stones. All horses need constant access to fresh, clean water.

The water requirement for horses at maintenance is around 60 mL / kg (1 oz / lb) of body weight per day. For a 500 kg (1,100 lb) horse, this amounts to approximately 30 litres or 7.9 gallons of water per day. ^[31]

Horses tend to drink more in hot weather and during exercise to replenish fluids lost while sweating. Several other factors increase water needs in horses, including:

• Lactation
• High-protein diets
• Illness or infection (diarrhea, fever, etc.)
• Stress and travel

Feed a Balanced Diet – Avoid Oversupplying Protein

A balanced diet ensures horses receive optimal levels of essential nutrients, including protein, vitamins, minerals, and carbohydrates. While protein is crucial for muscle development and immune function, excessive intake can strain kidney function. ^[32]

When horses consume more protein than needed, excess nitrogen is metabolized and excreted primarily as urea in urine, with some in the feces. This can lead to increased water consumption as the body tries to eliminate excess urea. ^[32]

Increased sweating and urine output occur as the body works to eliminate surplus nitrogen, disrupting fluid balance and metabolism. The kidneys undergo increased stress from processing excess nitrogen, potentially impairing function over time. ^[32]

To ensure your horse’s dietary needs are met while avoiding excesses that could strain the kidneys, consult with a qualified equine nutritionist for a tailored diet plan.

Summary

The urinary system in horses filters waste from the blood, regulates fluid balance, and removes excess metabolites through the production and excretion of urine.

• Monitoring urination patterns is important for equine management, as changes can indicate various health issues
• Hallmarks of urinary system dysfunction include excessive thirst and urination (polyuria and polydipsia), frequent urination (pollakiuria), painful urination (dysuria), and blood in the urine
• Diseases and conditions that affect the urinary system may be infectious, non-infectious, or congenital
• Endocrine conditions like PPID/Cushing’s and EMS can impact urinary function, often manifesting as polyuria and polydipsia.