Food and Feeding
The phrase used most commonly by sulcata owners to describe their tortoises is "eating machine." Sulcatas graze and forage for hours during the day. In the wild, much of their intake is from extremely hard to digest tough plant fibers from grasses. In captivity, a wide variety of vegetables and fruits can be offered (see list below) but sulcatas, like all tortoises, need to be able to graze on pesticide- and herbicide-free grasses and weeds. While sulcatas may be successfully reared for the first couple of years in a small yard, larger specimens need lots of yard with forage for them. Lists of toxic plants are available which should be used to determine which plants to keep out of your yard.
Three of the most important factors in constructing tortoise diets are the calcium:phosphorous ratio of the food and supplements ingested, the amount and type of protein eaten, and roughage--lots and lots of roughage. Too much phosphorous, or too little calcium, will cause bones and shell softening and deformity, and impairs metabolism and organ function. Too much protein, and feeding the wrong kind of protein (such as vertebrates, invertebrates, and commercial mammal foods) or too much of certain proteins (legumes, soy and alfalfa hay products) will cause too rapid growth, kidney failure, shell deformities and decrease life span. Studies of the feces of wild tortoises have shown that they do not ingest much in the way of animal protein. The animal component found in the feces was no greater than the small amount of other nonfood items such as small stones, feathers, fur and lizard skin sheds: in short, whatever was in the way as they were grabbing at their plants of choice (Highfield). Necessary protein may easily, and should, be supplied by plant proteins.
For roughage--to help provide the highly fibrous forage they eat in the wild--use hay flakes. Found at feed and grain (farm and ranch supply) stores, flakes can be put down for them to bite into and move around. Flakes are usually easier for most humas to lift and carry, and transport in their cars. If you can handle a full bale of good grass, that's fine, too.
Other food concerns include:
Too many "wet" foods, such as fruits, vegetables, and leafy greens, including the nutrition-poor, water-rich lettuces, and the healthier greens such as collards, dandelions, etc.
Feeding of too much goitrogenic vegetables, such as broccoli, Brussels sprouts, kale, cabbage and bok choy. In excess, compounds in these vegetables can impair thyroid function and cause goiter. Since you are going to keep these vegetables and greens to the level of occasional treats only, excess goitrogen intake shouldn't be a problem.
If you are considering using a commercial tortoise food product, check the ingredients. The main ingredient in most of them is soy. Most also contain a lot of corn, an ingredient whose key contribution to the mix is that it is cheap.
Foods which have fats added, and fatty foods (including soybean derivative) should be avoided as well. Fat impedes calcium metabolism and in general is not well metabolized by herbivores; liver damage and inability to retain Vitamin A result.
Care must be taken when feeding greens high in calcium oxalate (parsley, spinach, rhubarb, beet greens, collards, carrots tops, etc.) as the oxalic acid binds calcium. Fed in high enough quantities, it may not only cause metabolic bone disease due to preventing the metabolism of enough calcium, it may also cause visceral gout, the mineralization of the soft tissues and internal organs.
Cactus fruits, plantain, and desert mallow are plants favored by California desert tortoises which may be well received by sulcatas. Other California/southwestern native plants which seem to be preferred by desert tortoises include red-stem fialree, threeawn, red gramma, as well as rattlesnake weed, six weeks fescue, and the flower buds and stem tips of pencil cholla.
The bulk of their overall intake, however, should be from flake hay, pesticide- and herbicide-free grass and grass cuttings, cheat grass, clover, edible flowers (nasturtium, geraniums, hibiscus, rose petals and shrubs).
Fruits are very high in moisture fruits and should be fed in moderation to these tortoises who get little such free moisture in the plants they eat in the wild. Occasional small servings of fruits such as strawberries, chunks of organically grown bananas with skin, cantaloupe with rind attached, berries; peaches (no pits), apricots (no pits), pears, apples (no seeds) may be offered. Oranges and tomatoes may be fed, but not to hatchlings. Figs are a great source of calcium, but must be rehydrated if you can't find fresh ones out of season.
Sweet and colorful treats, such as fruit and edible flowers, are a great way to lure (bribe) your sulcata to go where you want him to go once he becomes too heavy to easily pick up and carry.
Sulcatas respond to bright colors and will try to harvest them on their own, so keep brightly colored inedible things away from them! You will also have to block their access to ornamental flowring and fruiting plants: a motivated sulcata will literally move walls and support posts embedded in concrete to get to something that interests them. (This also includes plowing through a screen door if they want to get inside the house...and do not assume that a few steps between the yard and deck will stop them once their legs are long enough to reach the bottom step.)
Sulcatas are prodigious eaters and are equally prodigious in the amount of waste products they will deposit around their environment. While sulcatas regularly ingest their own and other animal feces, they leave more than enough to keep any caretaker quite busy on a daily basis. Due to their coprophagy, fecal samples should be regularly tested to assure they are free from bacterial, protozoan and worm infestations.