Urinary Tract Infections in Horses
Unlike dogs, which commonly have urinary tract disease, urinary tract infections (UTIs) are very uncommon in horses, but they can occur.
- Foals less than a month old are at risk of developing upper urinary tract infections (affecting the kidneys themselves) secondary to bloodstream infections (septicemia).
- Critically ill foals that are given broad spectrum antibiotics to treat serious bacterial infections can (rarely) develop fungal infection of the lower urinary tract (affecting the urethra and bladder) caused by Candida sp. These infections can also “ascend” the urinary tract, eventually traveling from the bladder up the ureters to the kidneys as well.
- UTIs in adults are very uncommon, but when they occur they usually affect the lower urinary tract. Mares are slightly more likely to develop UTIs than geldings and stallions because they have a much shorter urethra, so it’s easier for bacteria to reach the bladder (they don’t have as far to go!).
Upper UTIs are very serious because the kidneys themselves are affected (nephritis), which can ultimately lead to kidney failure. Animals with this kind of infection are typically very sick, depressed, and can have a fever. In general, lower UTIs are not as serious, but they do make it very uncomfortable for the animal to urinate (the same is true for people!). However, lower UTIs that result in or are the result of stones in the urinary tract can be life threatening if one of the stones becomes lodged in the urethra, preventing the horse from urinating altogether (this is similar to the situation with “blocked cats,” which occurs relatively commonly). Most of these infections are caused by the same common types of bacteria – E. coli, Proteus mirabilis, Klebsiella sp., Staphylococcus sp., Enterobacter sp., Corynebacterium sp., Pseudomonas aeruginosa – but sometimes fungi can be involved (such as Candida sp.) and there are also some parasites which rarely can affect the urinary tract of horses.
The important thing to remember, though, is that these infections are uncommon in general, and they are very rare in otherwise healthy horses. So if a horse has signs of a UTI (e.g. difficulty urinating, unusual behaviour when urinating, frequenting “squirting” without emptying the bladder completely, scalded skin from urine dribbling, blood in urine), there is often something else wrong. An important predisposing factor is bladder paralysis, when a horse loses control of the muscles in the bladder wall that make the bladder contract. When the bladder can’t contract, it never empties, and the urine just sits there, allowing bacteria to grow and sometimes even allowing infection to travel up to the kidneys (i.e. ascending infection). Bladder paralysis can result from diseases or certain toxins affecting the central nervous system (e.g. equine herpesvirus type 1 (EHV-1), Sorghum spp. toxicosis). In horses, it is often difficult to determine if stones (uroliths) are the cause of a UTI or the result of the UTI.
As in any other animal, the best way to definitively diagnose a UTI is to culture bacteria from a urine sample that has been collected as aseptically as possible (usually by passing a catheter, as in the photo above). It’s important to collect a urine sample for culture before starting any antibiotic treatment. If you suspect your horse may have a UTI, it should be examined by your veterinarian as soon as possible.
