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.
equine urinary systemIllustration:

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 prote