Turtles in captivity have a tendency to suffer from nutritional shortfalls due to the fact that it is quite difficult to replicate their natural diet. They are omnivorous in the wild, which some people take to mean that they will eat anything. This results in their being fed just one basic type of food, often a proprietary brand, leaving them short of certain essential vitamins and minerals. Calcium is only one of the nutritional requirements of an aquatic turtle; shortages of vitamin A for example can cause quite severe eye problems. Also, turtles need unfiltered sunlight, as does any animal active in daytime, in order to manufacture vitamin D. It doesn’t take many minutes a day to ensure that the vitamin D level is adequate, but the calcium level in a turtle’s diet needs to be watched carefully, or a number of problems will soon become apparent.
Hatchlings and calcium deficiency
Many turtles bought from pet shops have odd-shaped shells and these never grow to look totally normal. This is because they have not had proper levels of calcium in the diet from hatching and so growth of the shell has been uneven. If the turtle is ever x-rayed for diagnostic reasons, it is often found that it has a scoliosis (curvature of the spine) as well as a deformed shell. These abnormalities are not always very obvious, but would show up if the animal in question was ever in a habitat with a turtle which had had adequate nutrition from the start.
Calcium and soft shells
Most people thinking of calcium deficiency think of shell and bone as the most affected area of a turtle’s physiology to show a problem. This is not true, as a lack of calcium affects a lot of other systems in the body, but a soft shell is certainly the most obvious. The shell is not always soft, but it will always be misshapen if there is a lack of calcium in the diet.
The shell is a kind of marker of the animal’s past nutrition, as the shell may harden when calcium intake increases, but a malformation will not correct itself later on. Calcium has to be actually eaten to do good, it is not absorbed by shell or skin, so many of the block supplements which well-intentioned owners place in the water of a habitat are not doing the turtle any good at all. Living in a hard water area is also not enough to prevent problems associated with low calcium levels.
Other problems associated with calcium deficiency
An unexpected side effect of a lack of calcium in the diet is anorexia. Commonsense would seem to dictate that if an animal is not getting enough of some essential food it would eat more to compensate, but this is not the case here. Calcium not only builds bones and shell, but is also essential for other functions, such as the effective contractions of muscles. This means that the peristalsis in the gut which is essential for moving food waste along for expulsion is weak and so the gut impacts, reducing appetite and making the animal lethargic into the bargain.
A lack of calcium also increases the incidence of turtles becoming egg-bound. This happens when a female is pregnant but cannot actually expel her eggs. This is again caused by the muscle contractions being weak and can be extremely dangerous for the turtle. Symptoms include excessive straining and restlessness. If you have reason to believe your turtle is gravid but she has not laid her eggs and is exhibiting this behaviour, she should be taken to the vet immediately. Sometimes an injection of calcium can be all that it takes but in cases where the eggs have been unlaid for a while there is no answer except to aspirate the contents of the egg to help it leave the body.
Making sure that a turtle gets enough calcium can be quite difficult, in that supplements are not easy to administer to an animal which prefers to eat its meals in the water; any powdered addition to the food will wash off before it is eaten. Feeding a mixed diet is the answer and again this is difficult especially in a habitat which supports several turtles, as it is next to impossible to see which animal eats what. The best course of action is to make the food as palatable as possible by allowing the turtle to take its food to the water where it prefers to eat, for the security it gives. This will mean that it will eat more as it is more comfortable and so is more likely to take in enough of everything it needs to stay healthy.
Omnivorous animals get a lot of their protein from meat of various kinds but will get most of their calcium from dark leaf vegetables, such as kale and spring greens. If the turtle likes it, fruit (not citrus) can also be offered and some really love peppers, so they should be included too. Proprietary brands of food are also very helpful, but they should not be fed exclusively, as the turtle will probably become quite bored with only one choice on offer and will possibly become anorexic. The best prevention is to keep an eye on the turtle’s general wellbeing because no two animals are alike in their requirements of vitamins and minerals – the best an owner can do is offer high quality food and keep watching the shell!