Here's a nice article written by a vet about removing stones from a desert tortoise:
http://www.lbah.com/word/tortoise-bladder-stones/
And this from Reptiles Magazine:
"The stones can be caused by a number of factors. The two most common are improper diet and dehydration. Tortoises are vegetarians. Like other animals, their diet should consist of protein, carbohydrates and fats. However, the dietary protein and fats should be of plant origin, not animal origin. Their systems are not equipped to handle large amounts of animal-based nutrients (such as dog food - a commonly fed diet that is very bad for tortoises and other herbivorous reptiles, such as iguanas).
This desert tortoise has a large bladder stone in the left lobe of the bladder (visible on the right side of the photo). The stone is pinching off the intestine, causing constipation.
You have probably noticed that when your tortoise defecates and urinates it produces a pasty white substance. This is called urates, which is the end product of protein digestion in reptiles. If that substance gets produced in excess it can crystallize within the tortoise's urinary system and form a stone.
If a tortoise becomes dehydrated, which can happen in captivity from either not being offered water or being offered food with a low water content, these urates can also crystallize within the body and lead to bladder stone production."
http://www.lbah.com/word/tortoise-bladder-stones/
And this from Reptiles Magazine:
"The stones can be caused by a number of factors. The two most common are improper diet and dehydration. Tortoises are vegetarians. Like other animals, their diet should consist of protein, carbohydrates and fats. However, the dietary protein and fats should be of plant origin, not animal origin. Their systems are not equipped to handle large amounts of animal-based nutrients (such as dog food - a commonly fed diet that is very bad for tortoises and other herbivorous reptiles, such as iguanas).
This desert tortoise has a large bladder stone in the left lobe of the bladder (visible on the right side of the photo). The stone is pinching off the intestine, causing constipation.
You have probably noticed that when your tortoise defecates and urinates it produces a pasty white substance. This is called urates, which is the end product of protein digestion in reptiles. If that substance gets produced in excess it can crystallize within the tortoise's urinary system and form a stone.
If a tortoise becomes dehydrated, which can happen in captivity from either not being offered water or being offered food with a low water content, these urates can also crystallize within the body and lead to bladder stone production."