Tortoises are herbivorous and, like herbivorous lizards, must consume plant material to maintain healthy gut physiology. Microbial fermentation of plant fiber can be a significant source of nutrients for tortoises. Diets of tortoises in the wild often contain >15% protein (dry-matter basis) in plant materials consumed, because natural vegetative materials are usually high in protein in the pre-seed stage, although a part of that protein is indigestible. Although small tortoises consuming pelleted diets can use plant fiber effectively, they should be fed more frequently than larger animals. Small and large tortoises can be maintained on appropriately formulated, extruded, pelleted, or coarsely ground tortoise diets.
Larger tortoises, such as Aldabra or Galapagos tortoises, can consume grass or alfalfa hay along with a complete pelleted food formulated for tortoises or exotic herbivores. Hay should be cut short, because the mouth shape of these tortoises makes it impossible for them to chew long hay. A vegetable mix consisting of broccoli, green beans, leafy greens (eg, romaine, green leaf lettuce, endive), kale, and shredded carrots may be fed as a supplement to a formulated tortoise diet. Such mixes contain adequate protein, calcium, and micronutrients; only limited vitamin and mineral supplements should be added. Cultivated fruits are typically poorer sources of protein, calcium, and micronutrients and, if fed in significant amounts, vitamins and minerals should be added. Some herpetologists offer oyster shell and pea gravel to tortoises, because “mining” activity has been seen in free-ranging animals. 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 deformities in tortoises have been thought to result from rapid growth associated with consumption of high-protein diets. Humidity and temperature also may influence shell deformation.