Horses normally have microscopic calcium crystals, even “sludge,” in their urine. Urine is normally alkaline (high pH), and these mineral crystals precipitate out at that pH, making the urine cloudy or milky at times. Urinary stones are formed predominantly by this same normal material, which has become concentrated in low urine volumes.
No one can truly explain why some horses form stones and some don’t, although they’re the most common urinary problem in horses. Age is a factor simply because it takes a stone a significant amount of time to become large enough to cause a problem. Stones are more common in geldings and stallions than mares because the male urethra, the tube that carries urine from the bladder to the outside, is narrower, longer and more twisted. Small stones that a mare would pass easily may be held up in a male horse.
Infection causes stones in other species, with the mineral deposits forming around a core of bladder cells and inflammatory cells. However, this material isn’t usually found in equine stones. It may seem logical that a diet excessive in calcium, which is excreted by the kidneys, may increase the likelihood of stones, but this hasn’t been confirmed — even though cloudy/milky urine is more frequent in a horse on mineral supplementation. What does make a difference, though, is the urine volume and how frequently the horse empties his bladder.
With below-normal urine volume, as occurs with chronically low water intakes or with diarrhea, the minerals become more concentrated in the urine and the horse doesn’t urinate as often. In addition, horses with bladder-motility problems have a higher risk of stone formation.
Even minor motility problems that don’t prevent the horse from urinating but do cause him to never completely empty his bladder will increase the likelihood of stones. Older geldings with inadequate sheath care often develop chronic infections, or even scar tissue, that make it painful or impossible for them to fully extend the penis and urinate a strong stream. This, too, results in the bladder not being completely emptied. (See sheath cleaners, September 2000.)
Stones may occur anywhere from the kidneys to the urethra, although they’re most common in the urethra and bladder. The bladder stones form when urine is not completely evacuated, and the urethral stones occur when stones from the bladder are washed into the urethra with urine and become lodged.
The primary symptom of bladder or urethra stones is blood in the urine. Bladder stones may not cause other symptoms, except for occasional trouble getting the urine flow started if they happen to block its exit. Stones in the urethra are more symptomatic, with changes in urine flow, multiple attempts to urinate and taking a long time to urinate. Complete blockage of urine flow rarely occurs.
Stones in the kidneys or in the ducts draining the kidneys (the ureters) can cause partial or complete blockage of a kidney. When this happens, the horse is colicky. The pressure buildup eventually damages the kidneys, causing renal failure. Unexplained weight loss is common. In some cases, neurological symptoms may occur, caused by high blood levels of the toxins normally excreted by the kidneys.
Traditional treatment of bladder or urethra stones is surgical removal. When surgery isn’t possible, the veterinarian may attempt to push the stones back into the bladder, hoping for the best. Medical treatment with ammonium chloride or high-dose vitamin C to acidify the urine usually isn’t successful, although their use is justified as a preventative with a history of treated stone disease.
A recent treatment involves lithotripsy, which uses intense sound waves to blast the stones into smaller pieces that may then be removed using scopes or in the urine flow. Successful nonsurgical resolution of stones by flushing the bladder with acetic acid and antibiotics every few days has also been reported.
Altered Bladder Motility
Abnormalities in the bladder’s ability to fully contract and empty are a common cause of stones and infections. Complete paralysis may occur, but more often than not, it’s a partial paralysis. Dribbling urine may be noted, but it’s more likely you’ll see no symptoms until secondary problems appear.
Altered bladder motility may be due to:
• Pressure on the nerve supply from old fractures, arthritic changes or tumors;
• Infections of the spinal cord regions involved in bladder control by Herpes virus or EPM;
• Scarring around the involved areas of the spinal cord resulting from prior epidural nerve blocks;
• Illegal alcohol tail blocks in show horses.
Abnormal bladder motility has no treatment option other than being vigilant for secondary complications. Any horse showing signs of irritation needs to be checked for stones or a bladder infection.
Bladder And Kidney Infections
Bladder infections basically only occur in conjunction with another urinary-tract problem, because most bacteria that gain access to the urinary tract are flushed out by the urine before they cause problems. Therefore, the most common causes of bladder infections in horses are:
• Altered motility of the bladder, with or without stones;
• Stone disease itself;
• Age-related conformational problems of the vagina that lead to excessive air in the vagina;
• Urine pooling in the vagina.
Infections may also travel up the ureters connecting the bladder to the kidneys, which causes additional infection in the kidneys and interferes with kidney function.
Reluctance to urinate is common, since it’s painful. This is usually caused by irritation of the urethra by the infection. Dribbling urine is common, as is grunting or tail swishing when urine is passed. Mares may also “wink” the vagina as if they are in season.
Urinalysis and urine culture are diagnostic tests. Treatment involves antibiotics, of course, but a thorough search should be made for an underlying cause of the infection.
Tumors And Cancer
Kidney tumors do occur in horses, but they rarely cause obvious symptoms until the mass has reached such a large size that it’s untreatable. The earliest symptom of kidney cancer, or cancer anywhere, may be unexplained weight loss.
Many people assume older-horse weight loss is inevitable or always related to inefficient chewing or digestion. While this is partially correct, there’s no steadfast reason why an older horse on an adequate calorie intake with feed of a type he can effectively eat should not stay in a reasonable amount of flesh. If your horse has lost weight for no obvious reason, get your veterinarian involved. If a kidney tumor is caught early enough, surgery may be an option for him.
More common is squamous cell carcinoma, a form of skin cancer, on the head of the penis. This may begin as only a small open area on the penis that fails to heal. For early cases, surgical removal of the abnormal area or cryotherapy (freezing) carries a good prognosis. However, if undetected until it spreads to local lymph nodes, the prognosis is grave.
Kidney Malfunctioning And Failure
Aging doesn’t cause kidneys to “wear out” and stop working, although malfunctioning — often called “kidney failure&rdq uo; even if the kidneys haven’t actually stopped functioning — is indeed more common in older horses. However, there are specific causes:
• Kidney cysts, probably a congenital condition that worsens with age as the cysts enlarge;
• Chronic low-grade infections;
• Partial obstructions from stones;
• Autoimmune disease attacking the kidneys as a result of a previous body-wide bacterial infection;
• Chronic diarrhea or other causes of chronic dehydration;
• Drug exposure, especially the chronic use of phenylbutazone.
A horse with low-grade, chronic kidney disease will often show no symptoms until as much as 75% of his kidney function is lost. In other cases, the disease may go undetected until an acute problem, such as use of the “-mycin” antibiotics or a course of phenylbutazone, tips him over the edge.
Once the disease reaches a critical level, the most common sign is weight loss. Loss of appetite and increased thirst with increased urination are also likely symptoms. If caught when urine production and water intake are increased, the chance that medical therapy can prolong the horse’s life is much better than if disease has progressed to the point that the horse no longer produces normal amounts of urine.
Step one is to remove any acute aggravating cause, like drug therapy. Free access to salt and water must be provided, unless edema develops, at which point you may need to restrict salt. Adequate but not excessive provision of minerals will help the horse maintain normal blood levels and avoid an increased risk of stones developing. Periodic blood checks to determine electrolyte levels will allow the veterinarian to recommend an effective supplement mixture for your horse.
As with any chronic disease, avoiding stress is important. The horse needs high-quality protein to maintain his muscle and body condition, but amounts must be restricted to avoid stressing damaged kidneys. B vitamins and anabolic steroids offer general support and help maintain muscle. Anabolic-steroid use is also beneficial in these cases.
Urinary-tract disease is basically rare in horses, but older horses are at higher risk. While kidneys don’t wear out, chronic problems with damage over the years may not appear until a horse is a senior.
Symptoms of kidney disease are often nonspecific, so any older horse with unexplained loss of condition should be screened for kidney and other organs disease. Male horses of any age are at higher risk for lower urinary-tract problems because of the anatomy of their urinary tract.