# Gut Loading



## Ed (Sep 19, 2004)

Given some recent comments, it appears that there is a need to discuss what actually constitutes gut loading, how it functions and the potential downside and upsides as it appears at least some posters lack essential knowledge on this practice. 

In the rigid technical definition gut loading is the process by which there is an attempt to modify the calcium to phosphorus ratio in feeder invertebrates. There are a number of studies that have analyzed this practice as either a direct practice for feeding the insects or to determine tolerances (example fruit flies) in culturing practices. The three most commonly analyzed feeder insects are crickets, mealworms and wax worms but this has also been done for fruit flies and silkworms. In general it is possible to achieve a positive calcium to phosphorus ratio (ideally between 1 and 2 to 1) in some feeder insects (mainly crickets, mealworms and wax worms) but it requires adherence to some rigid conditions to be successful and even within the same feeder insect there can be different variations depending on the maturity of the feeder insect (for example out of crickets, pinheads are the easiest to modify and adults the most difficult) and how palatable the feeder insects find the diet. The high calcium diet has to be the only diet fed to the feeder insects and water must be provided at all times. Fruit cannot be provided as a source of water as the feeders will consume the fruit and avoid the high calcium diet. If the feeder insects find the diet unpalatable then they will eat too little of it to achieve a sufficient calcium to phosphrus ratio. In addition, the diet has to be offered for at least 48 hours otherwise there is insuffient time to achieve a positive calcium to phosphorus ratio in the feeder insects. After 48 hours the feeders have to be fed out as the diet usually kills the invertebrates by 72 hours. Some feeders like fruit flies on analysis have been shown to be unable to be gut loaded with calcium as they have a very efficient method to excrete surplus calcium enabling them to keep the calcium at levels optimal for the fruit flies metabolic processes. In addition to the rigid condition requirements, it has to be kept in mind that the consuming animal is going to be unable to metabolize the calcium unless the animal has sufficient vitamin D3. A further item that needs to be monitored when attempting to modify the calcium to phosphorus ratios in the feeder insects when used in conjuction with supplements is the risk of too much calcium in the diet. Calcium has one of the narrowest safe ranges for a required nutrient and if the invertebrates are being fed a high calcium diet to the point where the calcium to phosphorus ratio is successfully modified and a calcium rich dusting supplement is also be adminstered then it is possible to over supplement calcium which can result in a conditional deficiency of zinc and other trace nutrients and in extreme cases combined with a high fat diet, calcium soaps forming in the digestive tract.


In the commonly utilized definition seen in the hobby, gut loading means feeding the invertebrates a diet percieved to be be nutritious to the invertebrate as well as the consuming animal. This is an area that for the most part has a lot of voodoo mixed into what we really do know. It is known that if you are getting your feeder insects from the pet store or a vendor, that due to the conditions and lack of food in shipping that they should be offered food and water for a minimal of 48 hours before offering them to the consuming animal. This allows the invertebrates to reaquire lost nutrients such as fats, protiens and trace nutrients before being fed out. When offering these foods to the invertebrates, diets that are high in oxalates (such as water cress) or goitrogenic plants (such as some members of the cruciferous vegetables and some soy products). The oxalate containing plants can interfere with calcium metabolism while the goitrogenic plants can cause thyroid issues if offered in excess. The problem with most of the gut loading recommendations in the hobby is that they are based on the idea the analysis of the food item is going to automatically carry over into the feeder insect. This is a problem especially given that unless the items are combined together in such a manner to prevent the feeder invertebrate from selectively feeding on selective portions of the diet. A further complication is that this process ignores the potential issues with stability of the combined ingredients. The combined ingredients may have issues with catalyzed oxidation due to fat soluble vitamin content, moisture and/or exposure to air. These can interfere with the goal of increasing the nutrition of the feeders. A further problem is that the items fed to the invertebrates should be selected with a goal to eliminate any contamination by pesticides and/or herbicides as there is evidence that these can bioaccumulate in either the feeder invertebrate cultures or in the bodies of the consuming animals. There is also some indication that at least in some caterpillars, gut loading diets may have little or no effect on fats and protien as analysis of the catapillers with and withoug the gut contents resulted in little variation in protien and fat. 
With this last version, when combined with a good dusting vitamin supplementation mlost of the risks can be readily averted. 

This is a partial list of references used in compiling this discussion. For some other information I refer those interested to the supplement article in the most recent issue of Leaf Litter. 

Bernard, Joni B.; Allen, Mary E.; Ullrey, Duane E.; 1997; Feeding captive insectivorous animals: nutritional aspects of insects as food, NAG publication

Crissey, Susan D.; Ward, Ann M.; Maslanka, Mike T. 2001, Nutrient content of nutritional supplements available for use in captive lizard feeding programs, pp. 53-59 edited by M. S. Edwards, K.J. Lisi, M. L. Schlegel, R. E. Bray, In Proceedings of the American Zoo and Aquarium Association Fourth Conference on Zoo and Wildlife Nutrition

Donoghue, Susan; Langenberg, Julie; 1996, Nutrition, pp. 91-98 edited by Douglas Mader, In Reptile Medicine and Surgery, W. B. Saunders Company, Philadelphia 

Donohue, Susan; 1996; Veterinary nutritional management of amphibians and reptiles, Journal of the American Veterinary Medical Association 208(11): 1816-20

Dube, K.A.; McDonald, D.G.; O’Donnell, M.J.; 2000; Calcium homeostasis in larval and adult Drosophila melanogaster; Archives of Insect Biochemistry and Physiology; 44(1) :27-39

Finke, Mark D.; Gut Loading to enhance the nutrient content of insects as food for reptiles: A mathematical approach; ZooBiology 22(2): 147-162

Frye, Fredric L., 1991, Reptile Care, an Atlas of Diseases and Treatments, TFH Publications, INC., Neptune

Hunt, Amy S.; Ward, Ann M.; Ferguson, Gary, 2001, Effects of a high calcium diet on gut loading in various ages of crickets (Acheta domestica) and mealworms (Tenebrio molitor), pp. 94-102 edited by M. S. Edwards, K.J. Lisi, M. L. Schlegel, R. E. Bray, In Proceedings of the American Zoo and Aquarium Association Fourth Conference on Zoo and Wildlife Nutrition

Li, H.; Vaughan, M.J.; Browne, R.K.; 2009; A complex enrichment diet improves growth and health in the endangered Wyoming Toad (Bufo baxteri); ZooBiology

Porter, Warren P.; Cole, Charles J.; Townsend, Carol R.; 1994, Captive maintenance and lineage senescence in parthenogenetic lizards (family Teiidae), edited by J. B. Murphy, Kraig Adler, Joseph T. Collins, In Captive Management and Conservation of Amphibians and Reptiles, Society for the Study of Amphibians and Reptiles. Ithaca 

Sabatini, Jeremy A.; Dierenfeld, Ellen S.; Fitzpatrick, Marianne P.; Hashim, Laurette; 1998, Effects of internal and external supplementation on the nutrient content of crickets, the Vivarium 9(4): 23-24

Wright, Kevin M.; 2001, Diets for captive amphibians, pp. 63-71, edited by K. M. Wright and B. R. Whitaker, In Amphibian Medicine and Captive Husbandry, Krieger Publishing Co., Malabar

Wright, Kevin M.; 2001, Nutritional disorders, pp. 73-83, edited by K. M. Wright and B. R. Whitaker, In Amphibian Medicine and Captive Husbandry, Krieger Publishing Co., Malabar


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## Enlightened Rogue (Mar 21, 2006)

Great post Ed, but I have to ask you one thing-do you ever sleep?
I haven`t typed that much in the 3 year`s that I`ve been here combined!!
I will say this-I always learn something.
Thank`s

John


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