Urolithiasis in Small Ruminants
Urolithiasis is a common disease of male sheep and goats. It is most often seen in castrated or wethered males, but may be seen in intact rams or bucks as well. Calculi or “stones” form in the urinary bladder, and partially or completely obstruct the urethra. The animal becomes uncomfortable and may be seen straining, stretching his hind legs behind him, and kicking or looking at his flank. The largest risk factor for development of urolithiasis is feeding grain or concentrates to wethers. Quick identification of urolithiasis in an obstructed animal increases the chances of treatment and survival.
Calculi form can form in urine when the pH is too high (alkaline) or too low (acidic), combined with elevated levels of minerals such as calcium, phosphorus, and magnesium. When the calcium to phosphorus ratio in a diet is less than 2:1, the animals are at an increased risk of developing struvite crystals in their urine, which solidify into calculi or stones. This is common in animals fed pellets or grain, as most grains are high in phosphorus and low in calcium. Phosphorus is usually recycled through saliva and excreted in manure, however excess phosphorus is excreted through the urine, leading to stone formation. Very high calcium levels in a diet can also lead to a rarer form of calcium carbonate stone. Other mineral imbalances may lead to different types of stone formation, each more common in different areas of the United States.
The calculi form in the bladder, and are passed in the urine through the urethra. In females and to some extent intact males, the urethra is larger, allowing the calculi to pass without problem. In castrated males the calculi become stuck, most often at either the very end of the penis, or at the sigmoid flexure (an “S” curve in the penis prior to it exiting the body), due to a narrower urethra from a lack of hormonal influences. The calculi become lodged in the urethra causing swelling and irritation. Initially it may not completely block the flow of urine, and you may notice dribbling urine, or blood-tinged urine spots present in the bedding. Untreated the calculi will completely obstruct the urethra from a combination of swelling, and physical blockage. This causes urine to back up in the bladder, and can potentially lead to rupture of the urethra or the bladder from the pressure.
This is a medical emergency, and veterinary assistance should be sought as soon as possible. Treating urinary calculi involves a combination of pain relief, attempting to dissolve the calculi, and surgical removal of the calculi if completely obstructed.
Preventing the formation of urinary calculi is one of the most important steps a small ruminant owner can perform. Unless they are severely under weight mature wethers rarely ever need any grain. Stopping grain feeding decreases the risk of urolithiasis. Young, growing animals should be fed appropriately for their stage of production, and if grain needs to be fed, a balance of 2:1 or greater, calcium:phosphorus ratio should be maintained. Castrated animals being fed grain may be fed ammonium chloride in their feed or loose mineral if there is a history of urinary calculi. Ammonium chloride acts to acidify the animal’s urine, which decreases the ability to form struvite stones. Animals treated long term with ammonium chloride will temporarily develop the ability to neutralize the ammonium chloride, so it should be dosed as needed on the recommendation of your veterinarian.