The tortoises have begun their fall slow-down and are preparing for their winter brumation (reptilian hibernation) here at the San Diego Zoo Desert Tortoise Conservation Center in Las Vegas. This means that the priorities in the medical center will shift a bit. We will have a few tortoises staying awake for the winter because they are either too sick or injured to brumate. However, we will also have a number of residents staying in the medical center waiting to have surgery at the state-of-the-art Harter Veterinary Medical Center, located at the San Diego Zoo Safari Park. All of these tortoises have dangerous uroliths that have developed in their bladder (uroliths are analogous to kidney and bladder stones in people).
Uroliths develop for various reasons, the most common being improper nutrition or prolonged dehydration. One of the adaptations that tortoises have that allows them to thrive in the arid desert environment is the ability to store large amounts of water in their bladder and to reabsorb it as the body needs it. As they reabsorb the water in their bladder, the solid particles in the bladder become more concentrated and can stick together. As time goes on more solids are deposited in the bladder and combine with those already present, forming a stone. Therefore, stones are more likely to form if a tortoise goes long periods of time without consuming fresh water to flush and replace the stored water.
Small stones that form can pass out of the bladder when the animal eliminates. However, once the stone becomes a certain size, it can be too big to pass and remains in the bladder where it can continue to get larger. If the stone is there long enough, it can adhere to the walls of the bladder, making it very difficult to surgically remove it without damaging the bladder. Eventually the stone can get large enough to take up most of the bladder space, thereby taking up very important water storage space. This compounds the problem by increasing dehydration in the tortoise. Eventually the stone can block the urethra, preventing the tortoise from eliminating at all and causing a build up of toxins in the tortoise. The long-term presence of uroliths can result in a prolonged, painful death.
We palpate every tortoise during its health assessment to see if we can feel a coelomic mass. Sand or gravel in the bowels or eggs can feel similar to uroliths during palpation, so we x-ray every tortoise in which we feel a mass to determine what the mass is. Once we have x-ray confirmation that it’s a urolith, we send the tortoise to the hospital, where veterinarian Nadine Lamberski has developed a less invasive technique to remove the stone. Traditionally, the most common stone removal technique used by veterinarians was to remove part of the plastron (the bottom part of the shell) to get to the stone. This procedure is very invasive and can take a very long time to heal since the bone of the plastron has to be removed. The veterinarians at the Safari Park use a technique in which they make an incision in the skin of the prefemoral area (just in front of the hindlimb) so they can access the stone and break it down and remove it without having to remove part of the shell. This surgery can take up to 6 hours to perform, but the recovery time for the tortoise is much quicker for this procedure. I am very excited to say that the veterinarians have performed a number of these surgeries successfully, and our tortoises have been able to return to us with a much better future in store for them.
We have a number of tortoises ready for surgery this winter. Once they recover, they will be able to be released to the wild Mojave Desert in the healthiest condition possible next year to live out their long lives in a natural environment.
Rachel Foster is a research associate at the San Diego Zoo Desert Tortoise Conservation Center. Read her previous post, Desert Tortoise Hibernation: Not for All.