Rams and wethers in feedlots or on high-grain rations are most often affected by urinary calculi, but the condition can occur in sheep on succulent pastures or on grain stubble. Rations high in phosphorus or rations with a phosphorus-calcium imbalance are most often associated with a high incidence of urinary calculi in feedlot lambs.
Urinary calculi occurs when salts that are normally excreted in the urine precipitate and form stones. The stones then lodge in the kidney, ureters, bladder, or urethra. Generally, affected animals stand with an arched back and strain to pass urine. An animal may kick at its belly, prefer to lie down, and become dull and disinterested in feed or water.
Preventing the disease by proper management is essential because treatment often is ineffective. Sheep must have a clean, constant source of water. Avoid excess phosphorus in the ration. When high-concentrate rations (which are high in phosphorus) are fed, feed-grade limestone can be added to the ration to increase the calcium level above the phosphorus level.
Adding ammonium chloride to a ration at the rate of 0.5 percent (8 to 10 pounds per ton), or about 0.25 ounces per head per day, is one of the most effective methods of controlling urinary calculi. Ammonium chloride can be included in pelleted or ground concentrate rations during the entire feeding period, but it cannot be effectively mixed with whole-grain rations because it settles out and is not consumed. Ammonium chloride also can be used as a drench for affected animals. Use up to 1.5 ounces per head, but administer only once at that level. Smooth-muscle relaxants may aid in passage of lodged calculi stones. Calculi also can be removed by surgery, but this is not practical for commercial sheep.
