Gut Loading Research Articles

Vitamin A, Vitamin E, and Carotenoid Concentrations in Livers of Marine Toads (Rhinella marina)

Global amphibian population decline is a major concern. Therefore, conservation centers have become increasingly needed for population sustainability breeding programs. This need makes proper nutrition programs while in human care imperative. The specific nutritional focus of this current research was to analyze vitamin A, vitamin E, and carotenoid (apocarotenoid, β-carotene, β-carotene ester, β-cryptoxanthin, lutein, lutein ester, zeaxanthin, and zeaxanthin ester) concentrations in the liver of 66 free-range marine toads (Rhinella marina) over a two-month period after entering human management. Toads were fed supplemented crickets randomly assigned to one of two diets: Diet 1 consisted of brown house crickets (Acheta domestica) gut loaded with Mazuri® Cricket Diet 5M38 and small amounts of sweet potato and carrots; Diet 2 consisted of an identical diet with the gut loaded crickets additionally dusted with Repashy® Superfoods Vitamin A Plus. Ten toads were euthanized prior to human management on Day 0 to assess baseline liver nutrients. Seven toads consuming each of the two diets (14 toads total) were euthanized on Days 9, 15, 32, and 62. Regardless of diet treatment, there were decreases (p < 0.05) in all the analyzed nutrient concentrations over the 62-day human management period. The results from this study indicate that higher dietary vitamin A, vitamin E, and carotenoid content may be needed and/or the cricket gut loading and dusting techniques used to feed the amphibians food source insects may be inadequate.

Using a Commercial Gut Loading Diet to Create a Positive Calcium to Phosphorus Ratio in Mealworms (Tenebrio molitor)

Mealworms ( Tenebrio molitor ) are one of the most common feeder insects fed to exotic animals due to their high acceptance rate, larval longevity, and ease of care. Unfortunately, in their natural commercial state, they are severely deficient in calcium and can predispose exotic animals to hypocalcemia and related metabolic disorders. Gut loading insects with calcium-rich diets is recommended to improve the insects’ nutrient content and to achieve a calcium to phosphorus (Ca:P) ratio of at least 1:1; however, there are few commercial gut loading diets specifically made for mealworms. In this study, mealworms were gut loaded with a newly developed high calcium mealworm diet for 0, 24, or 48 hours. All mealworms were analyzed for dry matter (DM), moisture, calcium, and phosphorus at each time point. Due to the dry nature of the diet, moisture content decreased over time (mean moisture content= 75%, 70%, and 66% at time 0, 24, and 48 hrs, respectively). Calcium content was significantly increased by 24 hrs (p=0.011) and remained elevated at 48 hrs for both the as fed and DM measurements (median calcium DM: 0.07%, 3.5%, and 3.7% at 0, 24, and 48 hrs, respectively). Ca:P ratios were also significantly increased for both the 24 hr (p=0.028) and 48 hr (p= 0.028) periods (median Ca:P DM:1:20, 3.2:1, and 3.6:1 at 0, 24, and 48 hrs, respectively). This data supports the diet’s claim to provide a positive Ca:P ratio in mealworms fed the diet for 48 hours.

Cane toad (Rhinella marina) vitamin A, vitamin E, and carotenoid kinetics.

Many amphibian species are threatened with extinction. Understanding their vitamin A (retinol), E (alpha-tocopherol), and carotenoid requirements is vital, as normal levels of these nutrients have a known connection to breeding success with abnormal levels leading to disease. This research examined vitamins A, E, and carotenoids (apocarotenoid, beta-carotene; beta-cryptoxanthin, lutein, zeaxanthin, and esters) concentration kinetics in the liver and plasma of 65 (57.8) cane toads (Rhinella marina) over 4 months supplemented with commercially available invertebrates in human care. Cane toads were opportunistically collected as part of a population control program for use as an amphibian model species. Toads were randomly assigned to one of two diets: treatment 1 was brown house crickets (Acheta domesticus) consuming Mazuri® Hi Calcium Gut Loading Diet without vitamin A or E supplement, plus fresh raw vegetables (carrot/sweet potato); Treatment 2 was the same diet except no vegetables. Ten toads were euthanized on Day 0 to analyze baseline free-ranging liver and plasma metabolites. Six toads consuming each treatment were euthanized on Days 22, 50, and 81, and n = 7 on Day 119 for analysis. Regardless of dietary treatment, most liver and blood metabolites were substantially higher at time 0 than all time points thereafter (p < .05); Ex: liver vitamin A at time 0 was 87.7 ± 16.12 µg/g while Day 119 for treatments 1 and 2 were 11.6 ± 1.19 and 8.2 ± 0.74, respectively. Few statistically significant differences between diets at the same time point were noted (p < .05). The results from this study indicate that additional or alternative diet supplementation may be needed for cane toads (and potentially other amphibians) to mimic their free-ranging diets.

Calcium Accumulation and Loss and Vitamin D3 Content of Feeder Black Field Crickets (Gryllus bimaculatus) Fed on a High Calcium Diet with and without UVB Irradiation

Calcium metabolism in insectivores may be perturbed by insufficient calcium or vitamin D3. Insects may be gut loaded to increase calcium content, and recent research shows that exposure to UVB radiation can increase the vitamin D3 content of some invertebrates. Typical gut loading protocols result in peak calcium content after 24–48 h, while existing evidence with UVB irradiation involves exposure periods of tens of days. We UVB-irradiated fasted black field crickets (Gryllus bimaculatus) while feeding them on high calcium diets for 48 h, then fasted them for a further 24 h, and measured the vitamin D3, calcium, and phosphorus content compared with non-irradiated controls. UVB irradiation had no effect on vitamin D3 (crickets had no detectable levels of vitamin D3 at any point), or on calcium accumulation rates, which approximated existing research. Crickets significantly increased their calcium:phosphorus ratio from 0.17 to approximately 0.4 over 24 h and this did not increase over a further 24 h of feeding. Removal of the food source resulted in loss of all accumulated calcium within 24 h. Our results have implications for managing food sources for captive insectivores and highlight the importance of good feeder preparation and rapid consumption to ensure optimal calcium delivery to predators.

The Value of Black Soldier Fly Larvae (Hermetia illucens) as a Food Source: A Review

Black soldier fly (BSF) larvae, commonly marketed as Calciworms® (Timberline Fisheries Corp., Marion, IL, USA) or Phoenix Worms® (Insect Science Resource, LLC, Tifton, GA, USA), have become increasingly popular as a feeder insect for reptiles. Their popularity stems from the larvae's potentially calcium-rich nature, capable of surpassing a 2:1 calcium to phosphorus ratio without the need for dusting or gut loading. Despite their popularity, there has been limited research regarding their use as a food item for reptiles. They have, however, been studied extensively in food animal production as a less expensive source of animal protein and as part of an integrated waste management system. This review is meant to provide exotic animal veterinarians with evidenced-based research regarding the BSF's natural history, standard rearing practices, and the larvae's nutritive value in various animal systems, including captive reptiles. The authors hope this review will help veterinarians make better feeding recommendations for their reptile patients.

Evaluation of vitamin A gut loading in black soldier fly larvae (Hermetia illucens).

Black soldier fly (BSF) larvae are potentially an excellent source of calcium for insectivores; however, previous studies have identified that they lack appreciable amounts of fat-soluble vitamins (A, D3 ,and E). To make BSF larvae a more complete food item, fat-soluble vitamins should either be provided via gut loading or with a multivitamin dusting supplement. The purpose of this study is to identify factors associated with gut loading vitamin A into BSF larvae and to develop feeding recommendations for a more consistent gut-loading process. Factors that were addressed include the vitamin A concentration added to the diet, length of time given to gut load, moisture content of the diet, and density of larvae during feeding. Diets and larvae were analyzed for vitamin A concentration using high-performance liquid chromatography. Larval vitamin A concentrations increased in a nonlinear fashion with increasing dietary vitamin A. Length of time (F = 150.818, p < .001), moisture content of the diet (F = 41.436, p < .001), and larval density (F = 78.407, p < .001) were all found to be significant factors contributing to the larvae's gut-loading capacity. On the basis of our results and vitamin A recommendations from the National Resource Council for rats and poultry, gut-loading recommendations for BSF larvae when fed to insectivorous reptiles and amphibians are as follows: vitamin A concentration of diet between 16,000 and 20,000 mcg retinol equivalents/kg, gut-loading time period of 24 h, moisture content of the diet approximately 60%, and larval density between 0.1 and 1 larvae per each gram of moist substrate.

Digestibility of black soldier fly larvae (Hermetia illucens) fed to leopard geckos (Eublepharis macularius).

Black soldier fly (BSF) larvae have been marketed as an excellent choice for providing calcium to reptiles without the need of dusting or gut loading. However, previous studies have indicated that they have limited calcium digestibility and are deficient in fat soluble vitamins (A, D3, and E). In this feeding and digestibility trial, 24 adult male leopard geckos were fed one of three diets for 4 months: 1) whole, vitamin A gut loaded larvae; 2) needle pierced, vitamin A gut loaded larvae; or 3) whole, non-gut loaded larvae. Fecal output from the geckos was collected daily and apparent digestibility was calculated for dry matter, protein, fat, and minerals. There were no differences in digestibility coefficients among groups. Most nutrients were well digested by the leopard geckos when compared to previous studies, with the exception of calcium (digestibility co-efficient 43%), as the calcium-rich exoskeleton usually remained intact after passage through the GI tract. Biochemistry profiles revealed possible deficits occurring over time for calcium, sodium, and total protein. In regards to vitamin A digestibility, plasma and liver vitamin A concentrations were significantly higher in the supplemented groups (plasma- gut loaded groups: 33.38 ± 7.11 ng/ml, control group: 25.8 ± 6.72 ng/ml, t = 1.906, p = 0.04; liver- gut loaded groups: 28.67 ± 18.90 μg/g, control group: 14.13 ± 7.41 μg/g, t = 1.951, p = 0.03). While leopard geckos are able to digest most of the nutrients provided by BSF larvae, including those that have been gut loaded, more research needs to be performed to assess whether or not they provide adequate calcium in their non-supplemented form.

Effect of post-gut loading time on the macro-nutrient content of three feeder invertebrate species

Techniques for increasing the nutritional value of feeder invertebrates include dusting the prey items with a vitamin and mineral powder supplement, or providing the invertebrates with nutrient-rich food, called gut loading, prior to feeding to insectivores. However, the delay between gut loading of prey and consumption by insectivores varies according to feeding regime and may be considerable if prey is left in the vivarium. This study aimed to determine the effect of time post gut loading on the nutritional composition of three species of invertebrates, mealworms ( Tenebrio molitor larvae, approximately 23–30 mm), giant African land snails ( Achatina fulica , shell size 10–35 mm) and dubia cockroaches ( Blaptica dubia , approximately 20–30 mm). Feeder invertebrates were maintained on a dry commercial gut-loading diet, supplemented with fresh vegetables for 48 hours, after which the diet was removed. Samples of invertebrates (120 g of mealworms, 80 g of snails and 100 g of cockroaches) were taken for proximate analysis (dry matter, ash, crude fat and crude protein) at 0.5 h (excluding cockroaches), 1 h, 6 h and 12 h (excluding snails) using standard laboratory procedures. A one-way analysis of variance was performed to test for differences in nutrient content between time points in each species. Crude protein and fat contents of snails were significantly greater at 6 h compared to 0 h (P < 0.01). However, no other significant differences in nutrient content of snails or other species were detected at any time points. It is feasible that the increases in crude protein and fat of snails were a result of nutrient accumulation within the body. These findings indicate that in the species tested, with the exception of snails, delays of up to 12 hours between gut loading of the prey and their consumption by a carnivore are unlikely to affect the concentrations of macro-nutrients (protein, fat, dry matter and ash).

Turbidity effects on the feeding, respiration and mortality of the copepod Pseudodiaptomus stuhlmanni in the St Lucia Estuary, South Africa

The St Lucia Estuary is the largest estuarine lake in Africa and due to anthropogenic activities it has since the 1950s been kept isolated from its main source of freshwater, the Mfolozi River. Stakeholders are increasingly calling for a full reconnection of the historical linkage in order to initiate system restoration. Studies conducted to test the effects of turbidity on the copepod Acartiella natalensis and the mysid Mesopodopsis africana have shown that turbidity reduces the fitness of these species. The turbidity tolerance of the dominant copepod Pseudodiaptomus stuhlmanni has not yet been documented. The aim of this study was to determine the effects of turbidity on the feeding, respiration and mortality rates of P. stuhlmanni. Although chlorophyll a and phaeopigment consumption was negatively affected by inorganic silt, the use of natural silt resulted in more variable trends. In contrast, a positive relationship was found between total organic carbon (TOC) consumption and turbidity. The high ingestion rates in the highest turbidity treatments of the TOC experiments are attributed to gut loading of organically-enriched silt. High turbidity also resulted in increased respiration rates of P. stuhlmanni, highlighting the energetic demand of turbid environments. Compared with other previously studied St Lucia zooplankters, P. stuhlmanni appears to be relatively tolerant of high turbidity. However, as the overall effect on this species is also negative, it is concluded that the St Lucia Estuary needs to be protected from excessive silt inputs if its ecological integrity is to be sustained.

Challenges with effective nutrient supplementation for amphibians: A review of cricket studies.

Over the last 25 years, numerous studies have investigated the impact of insect supplementation on insect nutrient content. In light of recent nutrition related challenges with regards to zoo amphibians fed an insect based diet, this review attempts to comprehensively compile both anecdotal and published data in the context of practical application on this topic. Insects, primarily crickets, used for amphibian diets historically demonstrate low concentrations of key nutrients including calcium and vitamin A. Commonly used practices for supplementation involving powder dusting or gut loading have been shown to improve delivery of calcium and vitamin A, though often not reaching desired nutrient concentrations. The large variety of factors influencing insect nutrient content are difficult to control, making study design, and results often inconsistent. Formulation and availability of more effective gut loading diets, combined with a standardized protocol for insect husbandry and dietary management may be the most effective way to supplement insects for use in amphibian feeding programs. Ideally, the nutritional improvement of feeder insects would begin at the breeder level; however, until this becomes a viable choice, we confirm that supplementation of crickets through both gut-loading and dusting appear necessary to support the nutritional health of amphibians and other insectivores in managed collections.

Evaluation of Four Dry Commercial Gut Loading Products for Improving the Calcium Content of Crickets, Acheta domesticus

ABSTRACT Crickets, Acheta domesticus, are commonly fed special diets to alter their nutrient content (especially with regard to calcium) to make them a more complete diet for insectivorous reptiles and amphibians. Calcium-fortified dry diets are used by zoos to increase a crickets' calcium content and a variety of products are available in pet stores for the hobbyist. In this experiment we compare the moisture, calcium and phosphorus content of small cricket nymphs and adult crickets offered an experimental dry calcium-fortified gut loading diet with those fed four commercial dry diets. An unfortified dry diet served as a negative control. Crickets fed the experimental calcium-fortified dry diet and one of the commercial products (T-Rex® Calcium Plus™ Food for Crickets) contained sufficient calcium to meet the estimated requirements of insectivorous reptiles and significantly more calcium than those fed the other treatments. Crickets fed the other three commercial products contained no more calcium than t...

Evaluation of Various Calcium-fortified High Moisture Commercial Products for Improving the Calcium Content of Crickets, Acheta domesticus

ABSTRACT Crickets, Acheta domesticus, are commonly fed special diets to alter their nutrient content (especially with regards to calcium) to make them a more complete diet for insectivorous birds, reptiles, and amphibians. Typically calcium-fortified dry diets are used to increase the insects' calcium content. In this experiment we compare the moisture, calcium and phosphorus content of crickets offered a typical dry calcium-fortified gut loading diet and distilled water, with those fed several commercial products (two commercial “calcium-fortified cricket waters” and a calcium-fortified high moisture diet designed to provide both food and water). An unfortified dry diet served as a negative control. Crickets fed the calcium-fortified dry diet contained significantly more calcium than those fed the other treatments. Cricket phosphorus content was not affected by diet. In summary the commercial products tested were ineffective in increasing the calcium content of crickets fed these products. For that reaso...

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

AbstractA 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 µg retinol/kg), vitamin D (300 and 190 µg cholecalciferol/kg), vitamin E (140 and 140 mg RRR‐α‐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 µg retinol/kg), vitamin D (460 µg cholecalciferol/kg), vitamin E (660 mg RRR‐α‐tocopherol/kg), thiamin (5 mg/kg), vitamin B12 (650 µg/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 µg cholecalciferol/kg), vitamin E (70 mg RRR‐α‐tocopherol/kg), and vitamin B12 (226 µg/kg). Zoo Biol 22:147–162, 2003. © 2003 Wiley‐Liss, Inc.

Sodium uptake from the gut of freshwater- and seawater-acclimated ducks and gulls

The first possible regulator of plasma sodium ([Na]pl) and chloride ([Cl]pl) concentrations is the gut epithelium. Its in vivo role in uptake of ingested salt in birds with salt glands has not been evaluated. In the present study the anterior gut 22Na uptake rate was measured in freshwater-acclimated ducks (Anas platyrhynchos) and gulls (Larus glaucescens) and was then measured in the same birds after acclimation to 2/3 seawater. The 22Na was given orally in 7–10 mL of 171 mM NaCl. In ducks, seawater acclimation increased [Na]pl and [Cl]pl but not Na space; in gulls seawater acclimation increased Na space, but not plasma ion concentration. The rate of gut 22Na uptake was the same in ducks and gulls and was not affected by seawater acclimation in either species. As determined from the 22Na distribution between erythrocytes and plasma 3 h after i.v. 22NaCl injection, duck erythrocytes sequestered more (9.3% ± 0.4%) of the load than did gull erythrocytes (6.9% ± 0.3%) (P &lt; 0.001). Although gulls are better hyperosmotic regulators than ducks, there was no difference between the two species in the entry of sodium into the extracellular fluid volume from the gut. Immediately after oral gut loading with dilute saline, freshwater-acclimated gull [Cl]pl, increased more (2P &lt; 0.001) than could be accounted for by equilibration of the administered Cl within the extracellular fluid volume. After gut loading, the increase in [Cl]pl, of freshwater-acclimated ducks was less rapid and could be accounted for by extracellular distribution of the oral Cl load. In seawater-acclimated gulls, [Cl]pl decreased following gut loading, but was unchanged in seawater-acclimated ducks.

Effect of venous (gut) CO2 loading on intrapulmonary gas fractions and ventilation in the tegu lizard.

Studies were conducted to determine regional pulmonary gas concentrations in the tegu lizard lung. Additionally, changes in pulmonary gas concentrations and ventilatory patterns caused by elevating venous levels of CO2 by gut infusion were measured. It was found that significant stratification of lung gases was present in the tegu and that dynamic fluctuations of CO2 concentration varied throughout the length of the lung. Mean FCO2 was greater and FO2 less in the posterior regions of the lung. In the posterior regions gas concentrations remained nearly constant, whereas in the anterior regions large swings were observed with each breath. In the most anterior sections of the lung near the bronchi, CO2 and O2 concentrations approached atmospheric levels during inspiration and posterior lung levels during expiration. During gut loading of CO2, the rate of rise of CO2 during the breathing pause increased. The mean level of CO2 also increased. Breathing rate and tidal volume increased to produce a doubling of VE. These results indicate that the method of introduction of CO2 into the tegu respiratory system determines the ventilatory response. If the CO2 is introduced into the venous blood a dramatic increase in ventilation is observed. If the CO2 is introduced into the inspired air a significant decrease in ventilation is produced. The changes in pulmonary CO2 environment caused by inspiratory CO2 loading are different from those caused by venous CO2 loading. We hypothesize that the differences in pulmonary CO2 environment caused by either inspiratory CO2 loading or fluctuations in venous CO2 concentration act differently on the IPC. The differing response of the IPC to the two methods of CO2 loading is the cause of the opposite ventilatory response seen during either venous or inspiratory loading.

Ventilatory response to venous CO2 loading by gut ventilation in ducks

Venous CO2 loading was achieved in unanesthetized, spontaneously breathing white Pekin ducks by gut-ventilation to load CO2 across the intestinal circulation. Gut ventilation with air had no effect on breathing, while venous CO2 loading resulted in an increase in minute ventilation [Formula: see text]. Ventilation sensitivity [Formula: see text] when expressed as a percentage of [Formula: see text] obtained either without or during gut ventilation with air (15%∙mmHg−1; 1 mmHg = 133.322 Pa) was within the range of values previously recorded in birds by investigators using other techniques. An isocapnic hyperpnea, as observed in some other studies, was never seen using gut loading of CO2. These experiments have shown the efficacy of loading CO2 across the gut wall in ducks and this technique should prove useful in resolving the roles of the various CO2-sensitive receptor groups in increasing [Formula: see text] in response to CO2 loads.