Reptile nutrition and management of nutritional disorders (Proceedings)

There are thousands of reptile species worldwide and more reptile species are kept as pets than any other taxa. For as many types of reptiles that are kept, there are as many natural history strategies that these species demonstrate in their wild habitat.  The key to keeping healthy reptiles is to mimic their natural habitat as closely as possible.  Natural history dictates the type of habitat, diet, feeding behavior, feeding frequency, and seasonal differences in diet or behavior that need to be provided for the captive reptile pet.

Feeding strategies

Reptiles demonstrate a variety of feeding strategies ranging from herbivore, omnivore, carnivore, and insectivore diets.  Some species will demonstrate one feeding strategy as a neonate and juvenile, only to switch to another strategy when mature.  Many commercial diets are available for purchase where reptiles are sold as pets.  Pellet diets many represent total nutrition, however over or under-supplementation is possible when feeding these diets exclusively.  Natural diets comprised of plants and natural proteins can also be fed to provide a balanced and nutritious reptile diet.  Regardless of the feeding strategy employed, care must be taken to provide total appropriate nutrition for the species as nutritional deficiencies are common.  Ideally, a reptile will be fed a variety of food items incorporating both natural and commercial foods to provided total nutrition.  When purchasing commercial diets, it is important to read the list of ingredients to assess completeness, nutritional balance and to ensure quality.

Examples of herbivorous reptiles commonly kept as pets include the green iguana and numerous species of tortoises.  However, even these reptiles differ in the type of diet they require as tortoises often require more grass based fiber in their diets and should have free choice access to hay or grasses.  Herbivorous reptiles should not have animal protein in the diet including commercial diets for dogs.  Plant proteins are important for these species and can be provided in the form of vegetables and legumes.  Fresh dark green vegetables including Romaine lettuce, mustard greens, and collard greens should comprise 40-60% of the diet.  Commercial diets can comprise 30-50% of the diet or can be replaced with vegetables including kale, spinach, broccoli, beans, peas, and leafy lettuce.  Fruits are an inconsistent source of vitamins and trace elements but do provide some water content to the diet.  These should comprise less than 15% of the diet.  Providing the reptile pet with a diverse diet will encourage the animal to become more accepting of new dietary additions, provide environmental enrichment, and ensure that a complete diet is provided.

Omnivorous reptiles, such as box turtles, require both animal and plant proteins.  Plant proteins are the same as those provided for herbivorous reptiles.  Animal proteins can be provided through earthworms, fish, insects, and small rodents.  High protein, high calorie foods such as commercial dog and cat foods should be avoided.  Some commercial diets such as trout chow, turtle pellets, and low calorie dog food can supplement the omnivore's diet but should not exceed 20% of the total diet.  Diets high in protein, including ground meats or carnivore diets, can cause skeletal abnormalities in young, growing omnivorous reptiles including abnormal shell pyramiding seen in chelonian species.

Carnivorous reptiles, such as snakes, can be fed diets comprised exclusively of animal proteins.  Ideally, the prey is pre-killed in order to avoid injury to the reptile.  Whole prey diets generally do not need to be supplemented.  When fed to reptiles, adult rodents are complete with appropriate levels of vitamin D, calcium, and phosphorus.  Neonatal and juvenile rodents are also complete if there is ingested milk in the GI tract to compensate for a lack of skeletal calcium in these prey items. 

Insectivorous reptiles, such as leopard geckos, are primarily fed insects including crickets and mealworms.  Insects are widely available for purchase but wild caught insects can also be utilized.  Care needs to be taken to avoid feeding an insect that is poisonous to the reptile (ex. fireflies, Lampyridae family).  Insect exoskeleton composition is rich in phosphorous and diets comprised of insects are inherently deficient in calcium.  In order to overcome this imbalance, the reptile owner can feed the insects a diet rich in calcium prior to feeding it to the reptile.  This is referred to as ‘gut-loading'.  Alternatively, the insect can be coated with a calcium supplement prior to being fed to the reptile, referred to as ‘dusting'.  The reptile should only be fed as many insects as it will ingest in a short amount of time to avoid losing the calcium supplement to the environment.  Supplements that are commercially available for reptiles vary.  If a supplement is being used to balance a diet that is high in phosphorus and low in calcium, a phosphorus-free diet should be used.  If the supplement is being used to balance a diet limited by a finicky eater, then a balanced supplement with 2:1 calcium to phosphorus content is appropriate. Ideally, the food products in the diet will be balanced and additional supplementation is not needed.  Some supplements can have negative side effects and should be avoided on a long-term basis but can be useful for juvenile reptiles or reproductively active females.

Feeding frequency will vary with species, age, and amount of food offered at a feeding.  Younger reptiles have shorter time intervals between meals.  Snakes should not fast for months on end.  Reptiles are prone to obesity in captivity and should be fed based on body condition and exercise.  Uneaten prey should not be left in the enclosure.  A fresh source of water should be available at all times.  This can be in a bowl, swimming area, or by regularly misting the enclosure.

Nutritional disease of reptiles

Nutritional Secondary Hyperparathyroidism

Nutritional secondary hyperparathyroidism is common in juvenile reptiles and reproductively active females but can be seen in any reptile.  Reptiles fed herbivore or insectivore diets tend to have higher incidence of this condition.  The resulting disease, commonly referred to as metabolic bone disease, is multifactorial.  Low intake of dietary calcium, high intake of dietary phosphorus, and lack of vitamin D/UVB exposure can all result in the development of clinical signs.  These signs develop when the body's calcium stores are depleted and include sternal posture, muscle tremors, and inactivity.  Young animals have higher incidence of bone changes including fibrous osteodystrophy, pathologic fractures, and tooth loss.  The diagnosis of nutritional secondary hyperparathyroidism is made based on the patient's history, physical examination, and radiographic findings. Swelling of the long bones, fractures, and increase bony pliability may be clinically apparent.  Radiographically, a loss of overall cortical density and fractures may be apparent.  Treatment involves correcting the diet and environment to meet the husbandry requirements of the species.  Calcium supplementation is imperative in the form of calcium gluconate (100 mg/kg SQ, IM, Intracoelomic q8h) in critically hypocalcemic patients and calcium glubionate (10 mg/kg PO q12-24h) orally long term. Vitamin D can be administered but providing full spectrum ultraviolet light (UVB 290-320nm) is critical.  The light must not be filtered by glass or plastic and should be placed within 18 inches of the patient.  Cage rest is recommended and all climbing apparatuses should be removed to prevent trauma to soft bones.  If fractures are already present, these should be allowed to heal without coaptation as external splints and surgical repair are likely to fail due to the fragile state of the bones.

Hypovitaminosis A

Hypovitaminosis A is common in young, fast-growing chelonians in captivity.  It is most often the result of an inappropriate diet and is exacerbated by the fact that some turtles, notably box turtles, can be finicky eaters.  Clinical signs associated with hypovitaminosis A include lethargy, anorexia, bilateral blepharoedema, ocular and nasal discharge, pneumonia, diarrhea, and abscess formation (especially aural).  Chronic hypovitaminosis A results in squamous metaplasia of epithelial linings leading to thickening of membranes, decrease lumen size and drainage, and invasion of opportunistic pathogens. Diagnosis is made based on the patient's history and physical examination.  Vitamin A levels can be measured but response to therapy is diagnostic.  It is important to rule out other causes of clinical signs including primary bacterial pneumonia.  Cytology of exudate will reveal a predominance of squamous cells without inflammatory cells in many cases of hypovitaminosis A.  Treatment involves correcting the diet and environment.  Parenteral vitamin A can be administered but care must be taken to avoid overdosing the patient as skin sloughing can occur. When abscesses are present, these should be debrided and the patient placed on appropriate antimicrobial therapy.

Gout

Gout in reptiles occurs when uric acid is deposited into tissues secondary to renal failure.  Reptiles fed high protein diets may be predisposed to developing renal disease.  Some of these patients may demonstrate polydipsia but it is challenging to assess polyuria.  Often, the reptile suffering from renal failure will display inappetence, lethargy, and may present with varying degrees of edema.  Due to its chronic nature, patients with renal disease and gout will be cachexic and dehydrated.  Visceral gout occurs when uric acid is deposited in the organs causing organ dysfunction and metabolic derangements.  Articular gout develops when uric acid is deposited in the joints but this is not often clinically apparent.  Diagnosis of renal disease and gout in reptiles is difficult to confirm.  Blood work may show hyperuricemia and hyperphosphatemia.  Radiographic evaluation may reveal the presence radiopacities in joints or soft tissue. Cytology of affected joints may show evidence of uric acid crystals.  Evaluation of urine sediment may reveal renal casts that raise the suspicion of renal disease.  Therapy of chronic renal disease and gout in reptiles is often unrewarding.  The reptile kidney lacks loops of Henle making diuresis ineffective in managing hyperuricemia. Despite this, fluid therapy and maintaining appropriate hydration will help support the metabolic processes in the reptile patient.  Allopurinol (10-20 mg/kg q24h) will help prevent exacerbation of the condition and analgesia should be provided (meloxicam 0.2 mg/kg PO, IM, IV q 24h). 

Thiamine Deficiency

Adult, piscivorous reptiles fed a diet of frozen fish can become deficient in thiamine. These patients will demonstrate neurological signs that resolve with the addition of thiamine to the diet (vitamin B1, 25 mg/kg PO q24h x 3-7 days). 

Conclusion

Nutritional diseases of reptiles are preventable and are often associated with husbandry related dietary deficiency or excess.  It is critical that the reptile practitioner become familiar with the captive care needs of the species they are working with and with the products that are commercially available for their reptile-owning clientele in order to prevent, identify, and appropriately treat these conditions.

Resources

Exotic Animal Formulary, 3rd ed. Carpenter J.W. 2001. Elsevier, St. Louis, MO.

Manual of Exotic Pet Practice. Mitchell M.A. and Tully T. N. 2009. Saunders, St. Louis, MO.

Reptile Medicine and Surgery, 2nd ed. Mader D.R., ed. 2006. Elsevier, Philadelphia, PA.

The Veterinary Clinics of North America – Exotic Animal Practice; Renal Disease. Echols M.S., ed. 2006. W.B. Saunders Co., Philadelphia, PA.