Insectivorous reptile nutrition and disease (Proceedings)
In this lecture we will discuss the basics of insectivorous reptile nutrition, paying particular attention to the role vitamin A and Vitamin D play in a healthy diet. Captive animals that receive diets that contain deficient or excessive amounts of both these vitamins are frequently seen by veterinarians. Therefore, it is important that the reptile veterinarian be able to recognize signs of malnutrition and provide treatment as well as correct the diet.
Captive insectivorous reptiles can be difficult for the casual keeper to maintain. In addition to providing an appropriate captive environment that meets the animal's requirements for heat, light, humidity, etc., a complete diet must be offered. With so many variables to address, even the most dedicated and educated keepers rarely get everything perfect. It should be noted that wild "insectivorous" reptiles rarely limit their intake to just insects. Most species will eat any living thing that they can overpower and consume. This means that wild animals will consume smaller mammals, reptiles, amphibians, birds, fish, crustaceans, and arthropods besides insects. The limiting factor seems to be the ability of the reptile to overpower the prey and fit it in their mouths!Unfortunately the majority of insectivorous reptiles in captivity subside on a diet consisting solely of crickets and mealworms plus the occasional waxworm. There is nothing magical about the nutritional content of these insects, and in fact they are deficient in a number of nutrients (Vitamin A & D, protein, and calcium). The fact of the matter is these insects are easy to maintain and propagate; therefore they are the most readily available. Luckily, in recent years there has been interest in finding new food insect species for captive propagation. Some of the fly larvae offered for sale (ex/"Phoenix worms") purportedly have better nutritional profiles than those of crickets and mealworms. This author believes that provision of a diet as varied as possible is the best approach to maintaining insectivorous reptiles. The author has personally raised many species of insectivorous lizards on diets consisting of commercially available insects plus field collected insects with no additional supplementation. Many deficient insect diets can be completed with the addition of the occasional vertebrate prey animal or prepared meat diet (canned cat food, etc.).
Frequency of feeding captive reptiles is a topic of some debate. Some keepers advocate feeding insectivorous reptiles relatively large meals 1-2 times weekly. Many animals will get by with this type of schedule, but a more natural approach would be to offer small quantities of food daily. This approach keeps the animal active, and helps avoid problems such as food impactions or constipation. When feeding frequency is increased the keeper also has more chances to offer variety in the food items offered, as well as the method of presentation. This can help enrich the lives of captive reptiles and encourage more natural behaviors.
Vitamin and mineral supplementation is tricky, as the quality of commercially available products varies greatly, sometimes according to batch. Many zoos with nutrition departments produce their own vitamin and mineral supplements and perform frequent analysis for quality control. The greatest difficulty lies in the fact that we simply do not know the exact dietary requirements of all species so sometimes we are using a best guess when developing diets. It is relatively easy to recognize when a diet is completely inappropriate as the animals may develop overt signs of malnutrition. The greater difficulty is when malnutrition does not cause overt disease, but results in reproductive failure or a slightly debilitated state which makes the animal more susceptible to infectious disease. These cases are more difficult to figure out and correct.
Many vitamin and mineral supplements come in powdered form and are intended to be "dusted" onto the prey item prior to feeding. Success in delivering the supplement in this manner varies according to a large number of variables. Even products that stick well to a chitinous exoskeleton can be groomed off if the insect is not consumed in time. Do not assume that adequate amounts of supplement are being delivered via insect "dusting".
Most veterinarians are capable of making educated guesses regarding the level of supplementation appropriate for certain reptiles. All husbandry parameters need to be considered, especially lighting, when developing supplementation protocols. For example those animals that receive large amounts of natural sunlight exposure do not need to be supplemented with large amounts of Vitamin D. If an animal receives large amounts of natural sunlight plus a large amount of dietary Vitamin D, hypervitaminosis D can easily occur. Generally speaking, the author suggests that insect diets be supplemented with fat soluble vitamins 1-2 times weekly. Minerals and water soluble vitamins can be supplemented daily if desired.
A good rule to remember is that it is very difficult to maintain a healthy, robust captive insectivorous reptile without feeding it a varied diet of healthy, robust prey animals!