Urolithiasis or urinary stones, also called urinary calculi or uroliths, are common in small ruminants. They form when concentrated urine contains too much mineral allowing minerals to come together to form stones. Urinary stones can form anywhere along the urinary tract, including the kidneys, ureters (tubes leading to the bladder), bladder, or urethra (the tube that allows urine to leave the bladder and the body). Sometimes, these stones obstruct the urinary tract, preventing normal urine flow, which is why you may hear your veterinarian say the animal is “blocked”. Many factors can predispose an animal to develop urinary stone formation and subsequently urinary obstruction, including:
Limited access to water and diets consisting primarily of alfalfa hay or grain are common culprits in stone formation because they are high in certain minerals like calcium. Because of their anatomy, urinary obstruction due to stones is most problematic in male sheep and goats. Males have a long urethra, and some areas are very narrow, providing more opportunities for stones to become lodged, blocking urine flow compared to female animals. Urinary obstruction is more frequently observed in wethers (castrated) that have been early in life. This is because hormones like testosterone are essential for increasing the diameter of the urethra. If castrated early, the urethra remains narrower.
Depending on the duration of the obstruction, urinary obstruction caused by stones can result in different clinical signs. In mild or early cases of obstruction, the following clinical signs may be observed:
If the urinary obstruction is prolonged, additional symptoms that may occur, including:
A diagnosis of urinary obstruction is suspected based on the history and physical examination. A definitive diagnosis and assessment of disease severity can be determined with additional diagnostics. Some diagnostics that your veterinarian may perform include:
Treatment for urinary obstruction depends on the obstruction's location and the type of stone causing the obstruction. Some obstructions can be relieved with a minor surgical procedure under light sedation, while some cases require a more invasive surgical procedure necessitating the animal to be placed under general anesthesia. Severe cases are frequently referred to a veterinary internal medicine specialist for more extensive medical care. Additional treatments administered on a case-by-case basis may include the administration of fluids, pain medication, antibiotics, and other therapies to change the urine pH and help dissolve the stones.
The prognosis depends on the location of the stones, the type of stone involved, how long the animal has been obstructed, and if that stone has caused a portion of the urinary tract to rupture allowing urine to leak out into the abdomen or surrounding tissues. In the later, the animal may become systemically unstable and be quite sick. Generally, partial obstructions versus complete obstruction carry a more favorable prognosis, as does early detection and intervention. In some cases, obstructions can reoccur later in life.
Modifying the diet to reduce the abundance of certain minerals that develop into stones can help prevent stone formation. Sheep and goats should be offered high-quality grass hay, and alfalfa hay and grain should be avoided unless directed by your veterinarian. Most animals should not be provided grain or offered only small amounts at a veterinarian's direction. Loose trace-minerals formulated for goats can be added to the diet to help maintain mineral balance. All animals should always have unlimited access to fresh, clean water. A water purifier should be considered if the water source is high in minerals, and you can have your water source assessed by a local extension service. Male sheep and goats should be castrated later in life if possible, ideally waiting until they are at least six months of age. Notably, most animals can breed females before this time, and intact males should be separated from females until castrated to prevent unintended pregnancies.