Dietary Management to Prevent Horse Bladder Stones

Balance is relevant to many aspects of horse care and management—for their feet, effective riding, nutrition and body condition, and of course for pH (a measure of acidity or alkalinity), electrolyte, and fluid levels. Of those, the pH or degree of acidity of specific environments and fluids within the body and electrolytes must be maintained within very narrow parameters to keep your horse healthy.  A pH measure of 7 indicates a neutral solution such as distilled water whereas values below 7 are considered acidic and those above 7 are referred to as basic or alkaline.

One place where pH is particularly important is the urinary tract. Because equine urine normally has a basic pH (more alkaline than acidic with pH greater than 7) and is high in minerals, some horses are at risk of developing stones in their bladders, called uroliths, especially if their diet is high in minerals.

One way to prevent uroliths is to acidify the urine (i.e., decrease urine pH). As easy as it sounds, it’s actually quite tricky. According to a group of German researchers*, hay and feeds containing hay (green fodder) are known to stabilize urine pH, making it difficult to acidify the urine when desired. What isn’t known, however, is what exactly makes hay such a poor urinary acidifier.

The researchers fed four ponies six different diets, either with or without additional urinary acidifiers to better establish how those diets impact urine pH. They found that a variety of diets were capable of acidifying the urine. The most impressive decrease in pH, from 7.8 to 5.2, occurred when the ponies were fed straw or extruded straw with a urinary acidifier (ammonium chloride, methionine, monocalcium phosphate). In contrast, any diet—even those containing urinary acidifiers—that included fresh or preserved green fodder could not be acidified. Urine pH remained above 7.

The take-home message of these findings is not to recommend a diet of straw and urinary acidifiers for horses at risk of uroliths, but simply to bring attention to the fact that adding a urinary acidifier to a horse’s normal diet might not produce the desired result. In addition, many common urinary acidifiers are unpalatable (such as ammonium chloride) or ineffective unless very large doses are administered. For example, 1-2 grams of vitamin C per kilogram of body weight is equivalent to 500-1000 grams of vitamin C daily–that’s a lot of 1-gram tablets! Vinegar is not widely deemed an effective urinary acidifier, either. More research in this area is needed to find effective and palatable solutions to this clinical issue.

*Foren, G., J. Fritz, N. Dillitzer, B. Hipp, and E. Kienzle. 2014. Fresh and preserved green fodder modify effects of urinary acidifiers on urine pH of horses. Journal of Animal Physiology and Animal Nutrition 98:239-45.