The calculi themselves are typically composed of phosphate salts and their formation is dependent on numerous interdependent factors relating primarily to nutrition and management. Male goats have a small appendage at the tip of the penis that creates a very narrow end to the urethra and predisposes the species to urinary obstruction. Urinary obstruction is rarely seen in does due to anatomical differences. Other factors that can predispose to calculus formation include poor water intake and dehydration, increased mineral content of urine reflective of diet and increased urine pH. Additionally, vitamin A deficiency has been shown to increase calculus formation, and the occurrence of a urinary tract infection creates an environment within the bladder conducive of stone formation.
Many goats in southwest Missouri are fed grain as a part of the ration. Typically, grain rations are high in phosphorus and this can lead to the formation of phosphate calculi in the urine. Generally speaking, the higher the percentage of concentrate feeds in the ration the more likely that urinary calculi will be a problem. In certain instances, excessive mineral content of well water can also be a nutritional factor.
If urinary calculi do form and cause an obstruction the goat becomes restless and uncomfortable. They will often vocalize excessively and will constantly posture to urinate by stretching themselves out and straining. Of course, despite their repeated efforts, no urine is produced or at times, only a small dribble of urine is released in contrast to a normal stream. If nothing is done to alleviate the condition, the urinary bladder or urethra can rupture in 24-48 hrs. At this point, animals may still be treatable but it requires surgical intervention by your veterinarian.
If the problem is caught early, the urethral obstruction can at times be alleviated. The filiform appendage at the tip of the penis can be amputated if the obstruction is located at this site. Otherwise, a catheter is placed and the urethra is flushed to alleviate a more proximal obstruction. Unfortunately, this is often a difficult procedure in goats and surgical correction may be required.
Delaying castration until around 3 months of age to allow for proper development of the penis and urethra may help to prevent the disease. The most important means of prevention, however, is dietary management. The calcium to phosphorus ratio is the most important key factor in preventing calculus formation and should be in a 2:1 to 2.5:1 ratio in the overall diet. Unless required by the stage of production, goats should be fed a very limited amount of grain in the ration and be maintained primarily on pasture or a grass/alfalfa mix hay. Keeping clean, fresh water available at all times is also very important and in problem groups, adding up to 4 percent salt to the ration will encourage water intake and a natural flushing of the urinary bladder. Adequate levels of vitamin A in the ration are also important.
For goat producers, understanding the clinical signs of urolithiasis and the most effective means of prevention will help to reduce the number of animals lost to this condition.
Darren Loula, DVM, is a large animal veterinarian at Fair Grove Vet Service in Fair Grove, Mo.
