Current thoughts on reptile nutrition (Proceedings)
May 01, 2011
Reptile nutrition: carnivorous species
Most reptiles that are strictly carnivores have short, simple digestive tracts, like cats and dogs. Their main nutrient sources come in the form of fat (25-60%), protein (30-60%), minimal carbohydrate, and negligible fiber content. This group of reptiles is often one of the simple groups to feed as they accept whole prey items. Some examples of reptiles and amphibians in this group are snakes, monitor lizards, tegus, crocodilians, and aquatic turtles. The main issue with the nutrition of this group of animals is obtaining high quality food items and storage of these items.
Food itemsThese include mice, rats, rabbits, Guinea pigs, hamsters, fish, chickens and chicks.
Live vs. dDead
This is a topic of continual debate among reptile owners. In the author's opinion freshly killed or defrosted frozen prey items (< 3 months frozen) are the safest option for feeding. Vitamin E may break down after 3 months of freezing resulting in nutritional deficiencies. Vitamin E can be supplemented at 200 IU/kg of food. In many cases live prey items (rats and mice) can inflict severe trauma to a snake during a struggle or if left alone unattended with snake. If the snake is not in the mood for eating it may not move and allow the rodent to chew, resulting in severe trauma. This behavior is not clearly understood.
Fish prey items
Whole live fish or gold fish are often fed. These prey items should be in good body condition and fed a good diet prior to being fed to the reptile. Frozen fish, especially herring and mackerel (high fat content), over time may have a breakdown of fatty stores, resulting in the production of thiaminase and hypovitaminosis E. It is recommended that frozen fish (or any frozen prey item) be stored for only 3 months. Supplementation with vitamin E (200 IU/kg of food) and thiamine (50 mg/kg of food) may be necessary if this is the only food source.
Adult vs. young prey
Independent analysis has shown that frozen pinkie mice have a 0.79:1 calcium:phosphorus (Ca:P) ratio while adult mice have a 1.4:1 Ca:P ratio. Some people say that if you feed pinkie mice just after they have fed on milk that the calcium level increases. This appears to be logical; however, there are no published data to support this. The author advises that if you are feeding a number of pinkies that you supplement with a commercial calcium product.
Pelleted diets are now available for both aquatic turtles and crocodilians. Aquatic turtle diets are plentiful and may vary in their protein content, with most ranging around 40% protein. These diets are recommended as they are nutritionally balanced and very palatable. Crocodilian pellets are available from Mazuri and come in a variety of sizes from 0.5-cm to 4- to 5-cm pellets. These are also a good choice for crocodilians and large aquatic turtles; however, they must be fed in a ratio of ⅓ by weight of the whole prey item. This is because these pellets are 95% dry matter (DM) compared with 35% DM in whole prey items.
In the recent trade journals there have been advertisements for prepared sausage-like food items for snakes. These items are currently available for dogs and cats and could be used for carnivorous reptiles as well.
Reptile nutrition: insectivorous species
Insect-eating reptiles can be considered carnivores and have short, simple digestive tracts. Their main nutrient sources come in the form of fat (25-60%), protein (30-60%), minimal carbohydrate, and negligible fiber content. The main problem facing insectivorous reptiles and amphibians is the low diversity of food items offered to the pet. In many cases people become dependent on one or two food sources such as crickets or mealworms and the health of their pet deteriorates. Most wild insectivorous lizards consume dozens if not hundreds of species of insects. In the last few years a number of different insect species have been offered for sale including crickets, meal worms, super worms, wax worms, butter worms, phoenix worms, night crawlers, silk worms, goliath worms, fruit flies, and fly maggots. Of these, the butter worms and phoenix worms have the best Ca:P levels with a ratio of 2:1 where as crickets, meal worms and super worms have inverse Ca:P levels. In addition, wild insects can also be used as supplement feed. Care must be taken to collect in areas that are freeof insecticide spray. In addition, some insects such as lightning bugs have been proven to be toxic to bearded dragons.
Some companies are now offering canned invertebrate diets such as crickets in a can, caterpillars and snails in a can. Nutritional analysis has shown that these diets have the same nutritional content as live insect, however there palatability is in question. The caned snails have the highest Ca: P ratio of 12:1. Some species like Caiman lizard would probably do well on the canned snail diet.
Supplementation of all insects and canned diets with a calcium supplement is necessary. The most effective approach is to house feeder insects in a clean, appropriate enclosure with a low stocking density. The highest food quality should be offered, as the food you feed the insects directly translates into the nutrition that your reptile is acquiring. Commercial pelleted diets for crickets are available and this along with fresh water and some fresh vegetables will provide a good diet. Gut loading of insects has some merit. Certain diets high in calcium have caused gut impaction with crickets. Once again a well-balanced insect diet combined with dusting just prior to feeding to the reptile is the best option. New gelled water products appear to be a good way of feeding crickets water without the mess of an open water container. Some of these products have extra calcium; the nutritional verdict is still out on these products.
Reptile nutrition: omnivorous species:
Omnivores can be fed a variety of items from the carnivorous and herbivorous diets. The ratio should be about 75% herbivorous and 25% carnivorous. Some of these species, such as bearded dragons, are carnivorous as juveniles and herbivorous as adults. It is the author's opinion that these animals should be acclimatized to herbivorous food at an early age so the lizard becomes accustom to eating greens.
Many commercially prepared gel diets are available. The advantage of these diets is that they can be altered and medication can be added with ease. These can also be custom-made at home; however, when making these
gel diets you must be careful to design a nutritionally balanced diet.
Calcium & phosphorus content of selected foods
The following charts show the total amount of calcium and phosphorus in 1-cup portions of selected foods. One needs to look not only at the total milligram (mg) amount of calcium, but also the Calcium to Phosphorus ratio. This ratio should be close to 1 to o.5 for the best calcium absorption. The higher the phosphorus amount is compared to the calcium, the poorer the absorption of calcium in the body.