MSU Extension Sheep & Goats

What is urinary calculi?

Urinary calculi (or urolithiasis) is a condition where the urinary tract becomes blocked by calculi, or stones. These calculi are often phosphate salts, but they can be other substances such as silicates, calcium or oxalates. The blockage leaves the animal unable to void its urine either completely or partially, which leads to toxic waste products building up in the blood (uremia = build-up of and poisoning by urea) and eventually death occurs. Treatment is often not effective, making it a very serious condition, and the incidence rate can be high under certain conditions.

This condition is observed most often in young, castrated males. The reason for this is that males have a much longer and narrower urinary tract than females, and castrated males tend to have an even narrower tract due to lower testosterone levels during development. Blockages can occur anywhere along the tract but often are either at the small urethral process at the end or in the sigmoid flexure, an S-shaped curve between the bladder and penis. Calculi formation may occur with similar frequency in females, but they are rarely a problem due to the shorter and wider urinary tract. The good news is that this malady can be largely prevented with proper nutritional management; therefore, we classify this condition as a nutritional disorder.

Symptoms

An animal unable to void urine appears very uncomfortable. They will typically seem nervous or ill at ease, twitch their tail, vocalize and/or kick at their belly. They may arch their back and strain to urinate or may appear constipated. Their urine stream may be weak, intermittent or barely present. Blood and/or crystals are commonly present on the sheath. Either the bladder or the urethra may rupture within 1-2 days if left untreated, and the belly region will start to fill with urine; hence the common name of “water belly” for this nutritional disorder. Eventually, nitrogen-containing compounds and other metabolites will build up in the blood and cause uremia, quickly leading to death.

Treatment

As soon as a case of urinary calculi is noticed, Michigan State University Extension recommends examining feeding management. Adjusting the diet may be too late for the affected animal but may prevent the progression of this disorder in the rest of the feeding group. It is possible that acidifying the diet, as described later in this article, may have some therapeutic benefit if caught very early, but the success of this treatment is low. Treatment method and outcome depend on where the blockage occurs. If the calculi are at the urethral process (a thin structure extending from the penis), the process may be excised, which allows the calculi to exit. Be aware, however, that there may be more stones further up the tract than can pose more problems.

If the blockage is further up the tract, such as at the sigmoid flexure, pain relief medication or relaxants may be able to dilate the urinary tract and allow passage. A saline catheter may also be inserted into the tract in an attempt to flush the calculi out or dislodge it. However, it is very difficult to insert a catheter in most males, making this therapy often of low feasibility. If none of these methods work, more invasive surgical procedures may be attempted, but the success rate can still be low. The surgery required may be expensive and specialized, which may not be available or feasible for many producers. Therefore, it is imperative that feeding management is addressed as an initial treatment.

Risk factors

A key risk factor for urinary calculi is high phosphorus diets that have a calcium: phosphorus (denoted as Ca:P, percent calcium to percent phosphorus in diet) ratio less than 2. Nearly all energy concentrates fed (corn, barley, wheat) will be high in phosphorus and low in calcium, so addition of calcium is needed in nearly all finishing diets to ensure that the Ca:P is at 2. Higher levels of calcium to raise the Ca:P above 2 are also not recommended, as they may lead to bone growth defects. The disorder may be exacerbated by high levels of magnesium in the diet as well (>0.6%), so such diets should be particularly careful to have a proper Ca:P ratio.

Low water consumption is also a primary risk factor for calculi formation. A concentrated mineral solution in the urine provides more conducive conditions for calculi formation. Animals who are low in the social hierarchy may be limited in access to water, making it important to provide additional water access in these cases for free access of fresh, clean water for all animals. Also, be aware that water needs may be very high during extreme weather conditions, such as during a heat wave.

As previously stated, castration leads to a narrower urethra, thus posing potential problems for calculi passage. The earlier that castration occurs, the narrower the tract diameter will be. Therefore, it may be advantageous to castrate males at a slightly older age if your animals are having continual problems with this condition despite proper dietary management. For example, one might switch from castration with elastrator bands at birth to use of an emasculatome when they are 30-60 days old.

Prevention steps

Prevention of urinary calculi is mainly done through feeding management. First, make sure the Ca:P ratio is close to 2. In corn-based finishing diets, the addition of limestone at 1% of the diet as a calcium source will be sufficient but check your ration carefully and adjust accordingly to provide close to a 2:1 ratio. Also, keeping the forage content of at least 10% of the diet will be an additional protective factor. Not only will it allow for a more optimal rumen function, but the effective fiber content will stimulate saliva production and water intake. Legumes tend to contain higher amounts of calcium than grasses, so there is an option of using them to provide more calcium as well.

Consumption of salt (sodium chloride, or NaCl) will also stimulate water intake, thus helping dilute the mineral content of urine. Salt can be provided free choice as part of a mineral mix and/or included in a finishing diet. The best salt delivery method to ensure adequate intake is to deliver salt within the finishing ration. Typically, finishing diets formulated with 1% salt will encourage water consumption, thereby reducing risk. The type of salt chosen to include in a finishing diet could be a trace mineralized salt with a high sodium content (>90% sodium chloride) which may also serve to meet the trace mineral requirements of the animals.

Acidifying agents such as ammonium (NH₄) salts can be introduced to the diet for further protective measures. Ammonium chloride can be added at 0.5% of the diet during the finishing period. Make sure the formulation is correct, as 0.75% of the diet may inhibit diet intake and above 1% may lead to metabolic concerns. Salt (sodium chloride), ammonium chloride, and calcium additions to a diet can be incorporated into a pellet to minimize the risk of sorting. This may not be feasible for many farms, however, so it is important to add a binding acid such as molasses or perhaps vegetable oil to minimize the amount of fine material in a diet, thus reducing sorting and ensuring the animals consume the mineral additions.

As always, make sure that all animals have access to clean and fresh water at all times. Many people who specialize in feeding lambs put extra watering points in pens than what may normally be used in other sheep housing situations to be certain that water access is not limiting.

Urinary calculi is a serious nutritional disorder that will impact nearly all flocks that feed finishing diets to males unless proper measures are taken. This disorder can be nearly eliminated, however, with careful dietary management and making sure there is free access to fresh water for all animals.