Editorial by Prof. Simon Davies
Other than the goldfish, the most common pet for children was the humble tortoise and I had one called Fred as a child. Now and quite rightly too, legislation has prohibited us in the UK from owning this most beautiful, advanced reptile and they are few and far to be seen these days gracing fenced off pens in our municipal and country gardens.
However due to their very impressive longevity, there will be some remaining and in many parts of the world significant numbers will be kept in captivity and especially in our zoos and educational wildlife centres. With this in mind, I focus on aspects of tortoise nutrition and their health.
Diets of tortoises in the wild often contain >15 percent protein (dry-matter basis) in plant materials consumed, as natural vegetative based foods are usually high in protein especially in the pre-seed, young fresh stage, although some of that protein is often quite indigestible when older. Although small tortoises consuming pelleted diets can use plant fibre effectively, they should be fed more frequently than larger animals due to a comparably higher metabolic rate. Small and larger tortoises can also be maintained on appropriately formulated, extruded, pelleted, or coarsely ground bespoke tortoise diets. These are available from specialised commercial companies and suppliers.
Understanding the Natural Diet
Tortoises are herbivores and primarily consume plant material in their natural habitat. Their diet typically consists of grasses, leafy greens, fruits, and some succulents. Different species have evolved to thrive on various types of vegetation, so it’s essential to research the specific dietary preferences of your tortoise’s species.
High-Fiber Diet: A vital component of a tortoise’s diet is high-fibre foods. Grasses and leafy greens provide the necessary roughage to support healthy digestion. Fiber helps prevent digestive issues and keeps their digestive tracts functioning optimally.
Leafy Greens and Vegetables: Dark leafy greens, such as dandelion greens, collard greens, and mustard greens, are excellent choices for tortoises. Other vegetables like carrots and squash can be offered in moderation. These foods provide essential natural sources of bioavailable vitamins and minerals.
Limited Fruits: Fruits can be given as treats but should be provided in moderation due to their higher sugar content. Safe fruit options include apples, berries, and melons.
Calcium and Phosphorus Balance: A proper calcium to phosphorus ratio is essential for tortoises. An imbalanced ratio can lead to nutritional disorders like metabolic bone disease (MBD), which can be quite serious. To ensure the right balance, provide foods high in calcium, such as calcium-rich leafy greens and cuttlebone, while avoiding excessive phosphorus sources like high-phosphorus vegetables and commercial tortoise treats. Certain foods are toxic to tortoises and should be strictly avoided. Some examples include avocados, rhubarb, and anything treated with pesticides or herbicides.
Feed Supplements and Formulated Pelleted Diets: While a varied natural diet is ideal, some formulated pelleted diets can be used as a supplement or balancer ration. These commercial diets are designed to provide essential nutrients (water- and fat-soluble vitamins, macro-minerals such as Ca P and Mg, as well as trace elements like iron, zinc, copper, manganese, and selenium) that may be lacking in a tortoise’s regular diet. Always choose highquality products from reputable manufacturers.
Nutritional Diseases: As mentioned earlier, Metabolic Bone Disease (MBD) is one of the most common nutritional diseases in tortoises. MBD results from an improper calcium to phosphorus ratio, lack of exposure to UVB light, or insufficient dietary calcium. It leads to weak and deformed bones, shell abnormalities, and overall poor health. Exposure to natural sunlight is essential for tortoises, as it allows them to synthesise vitamin D3, cholecalciferol which aids in calcium absorption. If your tortoise is kept indoors, consider providing full-spectrum UVB lighting to simulate natural ambient sunlight conditions.
Young animals should be weighed regularly and should follow the growing curve to prevent too-slow or too-fast growth, which can cause permanent malformation of the carapace. Shell malformations in tortoises have been thought to result from too rapid growth rates associated with the intake of high-protein diets. Humidity and temperature also may play a role regarding shell deformation. To prevent MBD and other nutritional disorders, it is crucial to provide a balanced diet rich in calcium and vitamin D3, along with access to natural sunlight or UVB lighting. Another aspect to consider is that tortoises hibernate overwinter, and the diet must be carefully given when they become active again in the spring.
Always consult with a qualified reptile veterinarian or herpetologist for personalised advice on feeding and caring for your specific tortoise species, as individual needs may vary. It would also be wise to contact local zoos for specialist advice on housing, feeding and nutrition.
This Editorial was published in the September 2023 Edition of International Petfood Magazine.