horse urinary system

The urinary system of a horse – and how to spot problems!


  • You might think that you don’t really need to know about your horse’s urinary system, but it’s one of those things that it’s good to have some knowledge so that you can be alerted when things are not right.


While urinary and kidney problems are not common in horses, they can happen quickly and end in death. Think ruptured bladder.


horse urinating stance with back legs out

This stance without any urine is a very bad thing…


The urinary system has many functions

  • Your horse’s urinary system is excellent at getting rid of waste via urine, maintaining the correct balance of electrolytes, it helps maintain healthy blood pressure as well as help to regulate red blood cells. The urinary system also processes vitamin D.


  • This urinary system starts with a connection of the bloodstream to the kidneys. Kidneys come in pairs, and in the horse, they are about seven inches long and usually four to six inches wide. The kidneys filter the blood, removing waste while holding onto important things.


  • The kidneys then send this waste and filtered fluid through the pair of ureters to collect in the bladder. The bladder is essentially a storage area for urine. When the bladder is emptied, the single urethra transports the urine of your horse’s body.


Fun facts about the urinary system of the horse:


  • Your entire horse’s blood volume goes through the kidneys about 250 times PER DAY.
  • Your horse filters about 350 gallons a day, but only urinates one or two gallons a day.
  • The urethra of the mare is much shorter than that of a gelding or stallion.
  • The bladder is elastic, and triggers nerves when full that tell your horse to urinate. It’s the relaxation of a small muscle between bladder and urethra that lets urine flow. The muscular contractions of the bladder itself help things along.


As seemingly short and small as this system is, it’s vulnerable to certain malfunctions that can have a devastating effect on your horse. Let’s zip through a list of what you might come across and what you can spot.


  • Stones can develop in your horse, sometimes they start in the kidneys, sometimes in the bladder. Stones can cause difficulty urinating, pain, and colic. They can physically block the urinary system and can lead to a ruptured bladder, which releases urine into your horse’s belly, resulting in death.


  • Stones are made when smaller calcium carbonate crystals get together to create larger stones. Typical horse urine contains a lot of mucus at the beginning of the urine stream to lubricate the urethra to pass the tiny crystals, which are normal. You might notice that the urine is foamy at first – this is the mucus. Then, the urine becomes cloudy as it contains a whole lot of waste including those crystals.


  • Horses get into trouble when the crystals band together to form stones. Stones can be formed from calcium or phosphorus, so making sure the diet is balanced is a great place to start. Don’t overlook the mineralogy and pH of your horse’s drinking water as a factor, as well.


horse urine puddle under his belly

Yup, foamy and normal.


How do you spot urinary stones in horses?


You will have to notice if your horse’s urinary patterns start to vary. With stones, he might:


  • Dribble urine. In mares, you will likely see some skin irritation under the tail
  • Stand stretched out to urinate
  • Have smaller volumes of urine
  • Be in pain when urinating – grunting, straining
  • Show colic signs – wide stance, often with penis dropped for long periods of time or traditional colic signs – getting up and down, off feed, not drinking
  • Have blood in the urine, especially after exercise


Do not wait to call the vet! Often the only remedy to stones is surgery, although there are some laser technologies that may help in some cases.


The urinary tract can also become infected, causing great pain and even traveling to the kidneys, which may result in kidney failure and death.


  • These infections are painful and often produce a fever. You might notice blood or pus in the urine, and it’s likely that your horse is urinating frequently with a bladder infection.


  • A bladder infection can spread to the kidneys. Your horse will be reluctant to move, won’t eat, and be in a considerable amount of pain. Kidney failure can occur, which lets toxins remain in his blood. Over time, sometimes weeks, sometimes months, sometimes years, your horse will decline, lose weight, become weak, and need to be euthanized.


The good news


  • They are not super common in horses, but they are almost always a serious threat to their health. It’s beyond easy to obtain a urine sample and blood from your horse, so get the vet involved if you suspect anything is different or abnormal. You might save your horse’s life!


For more details on normal horse urine and what to look for, read this super thrilling article!