Nutrition

“What and how do I feed my tortoise?” is one of the top questions people have. It does not take much research to become completely confused about this. Part of the problem is that there is no such thing as a “perfect” tortoise diet. For that matter, we really don’t have a “perfect” diet for dogs, babies, or humans in general!

Our starting point are the guidelines that the Association of  Zoos and Aquariums’ Nutrition Advisory Group came up with. They suggest offering a diet with the following characteristics
  • Is nutritionally balanced. This basically means it meets the actual needs for calories, proteins, carbs, vitamins, etc.
  • Reasonably duplicates natural feeding behaviors. The animal should eat it much as they would in the wild as possible. If the animal slowly grazes all day, it is inappropriate to make it gorge in a few minutes.
  • The animal consumes consistently. We should offer things the tortoise will usually eat without forcing it, etc.
  • Is practical and economical to feed. It should be cost- and time-effective to offer the diet.

Natural Tortoise Diets

Most tortoise species follow a few basic rules in the wild. They generally live in places that are amazingly low in nutritious foods.  Even peak growth rain forests that look so lush have amazingly little usable foods most of the year.  
Tortoises are designed to live in places like this: they take food most other animals ignore or cannot live on, eat it slowly, digest it slowly, and spend most of their time sleeping so they can live on the small amount of nutrition they have taken in. They may roam an area the size of several football fields to find enough nutrition for the day. When they do find a pile of something tasty – fallen fruit, yummy flowers, carrion – they will gorge, then sleep (sometimes for weeks), then gorge again until it is all gone.

Seasons play a big role as well. During the dry season, they live on tough grasses, leaves, stems, and other drier foods that tend to be low in calories but high in calcium and fiber. During these lean times, they add very thin growth rings to the shell. When the rainy or wet seasons roll in, they gorge on flowers, fruits, and fungi bursting with carbohydrates, nutrients, and flavor. These periods spur growth and this is reflected in wide growth rings. This pattern of feast and famine probably plays a major role in overall health and shell development, preventing pyramiding, etc.

Compare this to captivity where we generally offer meals that are already high in calories and fats, and low in calcium and fiber, offer the same nutritional profile all year along with a similar climate all year, and greatly restrict their ability to exercise. It is no wonder that so many captive tortoises do so badly.

Most tortoises eat about the same things overall, but there are two general categories:

Herbivorous tortoises 

These eat almost entirely plants, and not even all plants equally since most eat few if any fruits. Most of these tortoises live in grassland or arid habitats, and many of them live in places where they often need to brumate in the cold season. They get about 75% of their calories from carbohydrates (sugars found in the plants), 20% from proteins, and the remaining 5% from fats (note: too much fat in their diet causes stomach disorders!) Most of the calories will come from plant matter although almost all tortoises will relish the occasional piece of meat. (Mader)

These tortoises get much of their needed metabolic water from the plants and the digestive processes, but they should still have access to drinking water.

A typical diet profile would be roughly 95% vegetation and vegetables such as grasses, hays, leaves, stems, flowers, “weeds”, and fungi, and less than 5% fruits or vegetables with seeds, and very little meat. (Mader)

Omnivorous tortoises

Forest dwelling omnivores (Red- and Yellow-footed Tortoises, Kinixys, Indotestudo and Manouria species, American Box Turtles, and most terrestrial turtles) tend to eat a wider variety of foods, usually including fruits and meats. Much of this is probably due to the lower availability of calories and nutrients in the wild foods. (The frequent heavy rains tend to wash the nutrients out of the soil and in response the plants tend to concentrate what little they can get in the fruits.) Most of these tortoises do not brumate, although they may aestivate in hotter or drier weather. They should get about 50% of their calories from carbohydrates, and 25% each from fats and proteins. (Mader)

Most omnivores drink more freely, or at least eat foods with higher water contents. Again, clean water should always be provided.

The typical omnivore tortoise diet would be 75% vegetation and vegetables, 20% fruits or vegetables with seeds, and 5% meats or high-protein foods. (Mader)

Prepared diets

You can get chows and other prepared foods for tortoises just as you can for dogs or yourself (think cereals and other processed meals). While there are several options that work nicely, the three most consistently recommended brands in the US are:

There are varying opinions about using prepared diets, ranging from those who use them most of the time, to those who never do. The arguments for prepared chows include:

  • They are well-researched with years of clinical trials.
  • They are an easy and cost effective way to offer all the nutrition the tortoise needs (when the directions are properly followed.)
  • They are quick and convenient to use.
  • They fulfill the AZA’s guidelines listed above.

Arguments against chows include:

  • Most use cereal grains, that even when processed are not a natural food source for reptiles (or humans according to some people).
  • The use of sweeteners. These are often called “addictive”, even when they are added to improve flavor and calories.
  • Improper nutrition. Many people feel that, whether we are talking about tortoises or people, there is just no way to replace a natural diet with a processed diet and be completely healthy.

Interestingly enough, there are also arguments against fresh food diets! 

  • Store bought foods have lost much of their freshness and nutritional value because of the time spent in transit and storage, and may be contaminated with substances such as chemicals or fungi.
  • It is difficult for the typical keeper to offer a truly nutritious and balanced meal that really suits the tortoise’s needs. Because you only rarely really know what the nutritional values of any given food item are, it is far too easy to overdo some nutrient while not offering any of another.

Natural or Prepared Diets?

People fall into one of these categories:

  • ALL PREPARED FOODS. People in this group are confident that the makers of the chow have created a
    solid, balanced, and nutritious diet for the animals, and appreciate the cost and convenience of the prepared diet.
  • MOSTLY PREPARED FOODS. This category feeds their animals mostly chows or kibbles, with some fresh foods on the side to add interest, variety, and to help offer micro-nutrients that may be missing from the chow. Many prepared food makers actually recommend this.
  • HALF AND HALF. Recommended by veterinarian Greg D. Harrison to prevent what he calls the “Improper Diet Cascade”. The idea is that the fresh and prepared foods will balance the weaknesses in the other half. He also points out some things to consider when using prepared diets, such as storing them to prevent rancidity.
  • MOSTLY FRESH FOODS. The idea here is that a good diet built on variety, balance, and locally available produce is the best food for most animals, but that prepared chows can offer some benefit as well, so they are used as a supplement to help ensure good nutrition, or when fresh foods are less available.
  • ALL FRESH FOODS. People in this category feel they can buy or grow foods that serve their animal’s needs well and/or that there are problems in commercial chows. (However, many experts feel that without more research and preparation than most people are willing to do, that it can be very difficult to ensure that the foods offered actually meet the needs of exotic animals.)

How Much to Feed?

This is another tricky area. Some people feel that the tortoise can regulate its own intake and cannot really be over-fed, while others worry about obesity and limit the intake. Either way, the key goal is to help ensure healthy growth and natural behaviors.

One way to determine this is to calculate the daily calorie need: the weight in kilograms, to the 0.75th power, times 32 gives us the “base metabolic rate” for any reptile. (WTkg^.75×32=BMR). The BMR is how many calories the animal needs when healthy but not active, such as being kept indoors in a smaller enclosure. You increase the daily calories offered for animals that are more active, i.e. mating, nesting, or reproducing, and reduce it for animals that are in any form of slow-down (approaching brumation or aestivation), or not well. See “Healthy Weight” and “Dosages and Guidelines” for more. (Mader)

Another, more convenient, solution is to roughly mimic the natural diet:

  • Offer a nearly unlimited amount of plants that are low in moisture and calories but high in calcium and fiber. This includes most grasses, hays, leaves, lettuces, sprouts, greens, flowers, stems, and fungi. This
    can also include vegetables that are low in sugars like bell peppers, cauliflower, and broccoli. Note that not all species eat items like grasses or hays, especially the omnivorous species.
  • Limit food items that are high in calories, fats, and proteins such as fruits, vegetables with higher sugar content like pumpkin, and any type of meat, including invertebrates.
    • With herbivorous tortoises, this sort of food should be limited to occasional meals or snacks.
    • For omnivorous tortoises, this category can be offered in small amounts (about the size of the tortoise’s head) more often, one to three times a week, for example.

Overfed tortoises will grow in ways that may not be healthy. One study found that tortoises fed free amounts of Mazuri Tortoise Diet added height and width to their shells without adding length (Lickel). High calorie
foods can cause obesity, limit the tortoise’s ability to retract or breathe, and affect internal organs.

It is almost always better to underfeed a captive tortoise because of the limited amount of exercise they can get and because most of the foods we offer are so much “richer” in nutrients than the wild diets are.

Resources

Revised 5-29-2012. (C) Mark Adkins