Gut loading to enhance the nutrient content of insects as food for reptiles: A mathematical approach

Abstract

A variety of commercially raised insects are fed to insectivorous reptiles, but information concerning appropriate diets used to feed these insects is limited. In the present study, house crickets (Acheta domesticus adults and nymphs), mealworms (Tenebrio molitor larvae), and silkworms (Bombyx mori larvae) were fed diets containing graded levels of calcium (Ca) and/or vitamin A-nutrients that are low or absent in most insects. Diets and insects were analyzed for moisture, Ca, phosphorus (P), and vitamin A. For adult crickets and cricket nymphs, body Ca and vitamin A concentrations increased in a linear fashion with increasing levels of dietary Ca or vitamin A. Ca concentrations of silkworms also increased in a linear fashion with increasing levels of dietary Ca. For mealworms, body Ca and vitamin A concentrations increased in a nonlinear fashion with increasing levels of dietary Ca or vitamin A. These regression equations, in conjunction with insect nutrient composition, allow for the calculation of the optimum nutrient concentration for gut-loading diets. Final recommendations were based on National Research Council (NRC) requirements for rats, adjustments for the energy content of the insects, and nutrient overages as appropriate. Gut-loading diets for crickets (adults and nymphs) should be supplemented to contain the following nutrients, respectively: Ca (51 and 32 g/kg), vitamin A (8,310 and 5,270 mg retinol/kg), vitamin D (300 and 190 mg cholecalciferol/kg), vitamin E (140 and 140 mg RRR-a-tocopherol/kg), thiamin (31 and 21 mg/kg), and pyridoxine (20 and 10 mg/kg). Gut-loading diets for mealworms should be supplemented to contain the following nutrients: Ca (90 g/kg), iron (51 mg/kg), manganese (31 mg/ kg), vitamin A (13,310 mg retinol/kg), vitamin D (460 mg cholecalciferol/kg), vitamin E (660 mg RRR-a-tocopherol/kg), thiamin (5 mg/kg), vitamin B 12 (650 mg/kg), and methionine (29 g/kg). Gut-loading diets for silkworms should be supplemented to contain the following nutrients: Ca (23 g/kg), iodine (0.7 mg/kg), vitamin D (140 mg cholecalciferol/kg), vitamin E (70 mg RRR-a-tocopherol/kg), and vitamin B 12 (226 mg/kg).

Insects as Food for Insectivores

“…Calcium levels are typically less than 0.3% dry matter (Barker et al, 1998;Finke, 2002Finke, , 2013Oonincx and van der Poel, 2011;Oonincx and Dierenfeld, 2012;Punzo, 2003). The higher levels of calcium occasionally reported for feeder crickets likely reflect calcium in the gut contents (Barker et al, 1998;Finke, 2003;Hatt et al, 2003;Punzo, 2003). The exoskeleton of most insects is primarily composed of protein and chitin, although some insects have a mineralized exoskeleton in which calcium and other minerals are incorporated into the cuticle (Dashefsky et al, 1976).…”

“…The same powder used for pinhead or adult house crickets could therefore have different effects on their chemical composition (Sullivan et al, 2009). Similarly, for gut-loaded insects, size differences could lead to differences in nutrient delivery of smaller versus larger insects (Finke, 2003(Finke, , 2005.…”

“…Because the contents of the gastrointestinal tract can represent a significant percentage of the total weight of the insect (Finke, 2003), it can have a significant effect on the mineral content of the insect if it is analyzed when fully fed. Additionally studies of wild insects show both seasonal variation as well as variation between different populations of the same species living in the same general area (Finke, 1984;Studier et al, 1991;Studier and Sevick, 1992).…”

The effects of prey species on food conversion efficiency and growth of an insectivorous lizard

“…The nutrient and fiber content of house crickets and mealworms has been well documented [Pennino et al, 1991;Barker et al, 1998;Finke, 2002Finke, , 2007. In addition, research has demonstrated that the nutritional quality of cultured insects can be improved by feeding them (gut loading) food that has been fortified with specific minerals and vitamins [Anderson, 2000;Klasing et al, 2000;Finke, 2003;Winn et al, 2003]. However, as far as can be determined, nothing has been reported on the effects of feeding exclusively crickets or mealworms on growth parameters of insectivorous lizards.…”

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“…Knowing the weight of the insects and the amount of food in its gastrointestinal tract might allow zoo nutritionists and veterinarians to use insects to deliver a wide range of other compounds, such as carotenoids and pharmaceuticals (e.g. anthelmintics) to captive insectivores (Finke, 2003). Insect protein is readily available with protein quality values similar to, or slightly higher than fish meat or soybean meal.…”