– Michelle Arnold, DVM (Ruminant Extension Veterinarian, UKVDL), Dr. Jeff Lehmkuhler, Beef Extension Specialist, University of Kentucky
“Urolithiasis” is the veterinary term used for the disease resulting from the formation of stone-like structures (“calculi”) inside the urinary tract of cattle, similar to kidney stones in humans. If a stone lodges in the urethra, it can partially or completely block the flow of urine and eventually lead to rupture of the bladder or urethra and ultimately death. Emergency surgical intervention may be performed or humane euthanasia recommended due to the extremely painful condition in affected animals. Stone formation is due to many factors but high phosphorus/ low calcium intake is perhaps the most important cause. Corn and corn-based coproducts such as dried distillers grains and corn gluten feed both have high concentrations of phosphorus and low calcium content. When feeding these feedstuffs without supplemental calcium to maintain at least a 1:1 ratio of calcium to phosphorus (2:1 is preferred), the potential for bladder or kidney stone formation increases dramatically.
How do urinary calculi form? Stones begin as a small accumulation of cells, mucus or bacteria floating in the urine in the bladder or kidney. For a steer on a high grain diet with incorrectly balanced minerals, the urine pH is typically alkaline (or basic) and contains mucoproteins and minerals including phosphorus and magnesium in liquid form. If the steer is not drinking adequate water, the urine becomes concentrated and the minerals begin to change to their solid form and stick to the small clumps of cells. The mucoproteins serve as the glue that holds it all together.
The most common types of stones identified from cattle on grain diets are “struvite” (magnesium ammonium phosphate) or “apatite” (calcium phosphate) calculi. Excess phosphorus and magnesium in the diet, low water intake and urine alkalinity all contribute to this condition. Other types of stones are possible depending largely on the diet. Calcium carbonate stones occur more commonly in forage-fed animals, calcium oxalate stones may be seen if ingesting oxalate-containing plants and silica stones can form when grasses have high silica content.
Is this only a problem in steers? Urinary calculi are mostly problematic for feedlot steers, and less often seen in bulls or females. The male urethra (the tube that transports urine away from the bladder) is a long and winding road from the bladder to the outside of the body (see Figure 2). Stones most often lodge at the “sigmoid flexure”, an “S” shaped curve in the urethra. Early castration may reduce the diameter of the urethra, making steers more susceptible to stones lodging and completely cutting off the flow of urine. Females are rarely affected because they have a shorter and wider urethra that makes passage of stones much easier. Bulls can suffer from this condition but it is less common than steers.
How do I recognize a steer with urinary calculi obstructing urine flow? The first indicators are depression, no interest in feed, labored breathing and walking stiffly. Crystals may be observed on preputial hairs (Figure 3). Early clinical signs look similar to a digestive upset or colic. The steer will lick or kick at his belly, stomp his rear feet, and switch his tail. Attempts to urinate are frequent, with straining and grinding the teeth. Excessive straining can cause the rectum to prolapse and may be confused with constipation. If urine can pass, it often dribbles out and may be blood-tinged, and sometimes urine is completely absent.
When the obstruction is complete, the urethra or bladder will finally rupture. Rupture of the urethra results in swelling in the prepuce and scrotum (see Figure 4), and the diffusion of urine under the skin of the belly cause the swelling to extend toward the chest. The penis may be swollen and protruding. Rupture of the bladder causes urine to gather in the abdomen, causing a progressive distension of the flank areas (“uroperitoneum”). Rupture brings relief from the pain and the steer will seem relieved. There is a temporary improvement in attitude and the animal resumes eating but the abdomen continues to expand with fluid (urine). As urine accumulates in the abdomen, toxemia and death occur in about 48 hours after rupture. The gathering of urine under the skin or in the abdominal cavity is often referred to as “water belly”.
How do you treat a steer that is “blocked”? Routine observation of cattle is necessary to detect the earliest signs of disease. Timing is important because delayed treatment can lead to complications that lessen the chance of survival. Often surgery is needed to create a permanent opening in the urethra in the perineal area. These calves can be marketed after a period of time to eliminate tissue residues of urine and medications. Partial obstructions can sometimes be medically managed with urinary acidifiers, anti-inflammatories and phenothiazine tranquilizers but surgical management is often required.
How do you prevent urinary calculi? Most importantly, easy access to fresh, clean drinking water is essential. To increase water consumption and dilute the urine, increase salt in the feed to 0.25%-0.5% of the diet. The addition of ammonium chloride, fed at a rate of 0.5%-1% of the diet dry matter or 30-60 grams per head per day, will lower the urine pH to prevent formation of stones. Correction of the calcium to phosphorus ratio in the ration to at least 1:1 with 2:1 as the recommended target is mandatory. As a general rule of thumb, three pounds of corn gluten feed or dried distillers grains provides approximately the same amount of phosphorus intake as 4 ounces of a 6% mineral product. Therefore, it is necessary to provide additional calcium to maintain an adequate calcium to phosphorus ratio to prevent urinary calculi in corn-based diets and when higher levels of corn-based coproducts are used as supplements. Offer a high calcium, low phosphorus mineral (20-25% calcium and 3% or less phosphorus mineral) or use a coproduct balancer mineral pellet product in the feed. Adding feedgrade limestone to the diet at a rate of 0.1-0.2 pounds per head per day will increase calcium when feeding high levels of corn/corn-based coproducts. If grain intake is high, a switch to straight soyhulls or another feed that allows easier maintenance of the proper Ca:P ratio may be necessary.
In summary, formation of urinary calculi is a metabolic, nutritional and management issue. A diet high in grains causes an increase in mucoproteins in the urine. An improperly- balanced calcium to phosphorus ratio in the diet leads to increased phosphorus intake, and the high levels of phosphorus and mucoproteins, in an alkaline pH urine, results in stone formation. An additional factor that favors formation of stones is concentrated urine from not drinking enough water. Attention must be paid to the water source because clean and fresh water, close by and with plenty of space to drink, encourages adequate consumption.