I recently got into a debate with someone on another board about the safety of feeding rodents to bearded dragons in captivity, which motivated me to do some research on the subject and knock out an article on my findings. I'm posting it here in the hopes of it being some use, of interest, or receiving feedback for anything I might have missed or misunderstood. Feeding rodents to the inland bearded dragon (pogona vitticeps). One of the many topics up for debate within the bearded dragon community is that of feeding small rodents, such as pinkies, ‘fuzzies’, and sub-adult mice, to captive bearded dragons. A number of books and care sheets on the subject indicate that small rodents can be fed “occasionally”, with each source varying on what exactly they mean by “occasionally”; for some they mean every few weeks, for others every few months, and for some only when the dragon is underweight or gravid. A pertinent question to ask is ‘why do so many different sources have a different view on this issue?’, and ‘why are rodents being recommended to be fed more sparingly as time passes and more and more people own dragons?’. In this article I’m going to attempt to answer these questions, and give a basic overview of the pros and cons of feeding mammalian protein to our bearded dragons. The first issue to look at here is that of fatty liver disease; “Fatty liver, or hepatic lipidosis, which is the medical term, refers to a condition where the patient's liver is infiltrated with excessive fat.” In recent years there have been more reports within the community of dragons (usually ones rescued from improper conditions and husbandry) being diagnosed with fatty liver disease later in life. Although few actually seem to die from this condition, it does seem to be an indirect cause due to the damage it can do to the dragon’s overall health. Considering the varied diet that inland bearded dragons evolved for in the wild, and their voracious appetites, many have wondered just what part of our captive husbandry is causing the development of this disease in escalating numbers over the years. The main problem when attempting to ascertain why this disease has increased within captivity is simply the issue of lack of studies and research. There is just so much more literature on mammalian diseases, and responses to diseases, than reptilian, since herpetologists are a much smaller scientific group, and those herpetologists who have chosen to focus on fatty liver disease are, understandably, dealing with those reptiles that suffer from it most often; those of large herbivores like iguanas (who almost always develop the disease from being fed meat when they are obligate herbivores), and carnivores like Savannah monitors that are overfed due to how eagerly they respond to any, and all, food. There are little, to no, studies detailing fatty liver disease in omnivores like the bearded dragon, so one has to go back to basics to try to work out where the problem lies. Issue #1: Comparing studies on fatty liver disease in mammalian subjects to reptiles. A number of times when attempting to research this issue in regards to reptiles you will come across people using studies on mammals, such as humans and felines, in order to ascertain how fatty liver disease might effect reptiles. This approach is fundamentally flawed, and of no use to the average reptile owner, for a number of reasons: 1/ Mammals have an entirely different digestive system to reptiles 2/ As pointed out above, the main examples used when debating fatty liver disease are those of humans and cats. Cats are obligate carnivores and are therefore adapted for a diet high in protein and have livers capable of processing more calories from fat than an omnivore or herbivore; similarly, humans are omnivores with a digestive system evolved to eat mammalian protein, which is higher in fat than insects, hence why we're also better adapted to handle fat than omnivorous and herbivorous reptiles. Omnivorous and carnivorous mammals also have evolved a metabolism that allows us to burn off fat and calories at a much higher rate than reptiles, thereby assisting us in maintaining a safe level of fat within our bodies. 3/ Mammals are warm bloods (or endotherms) and therefore have a built in ability to burn fat, unlike cold blooded reptiles (ectotherms). In fact, reptiles do not even benefit from exercise like we do; they have built in aerobic and muscle mass genetic factors that are exceptionally hard to increase, unlike warm bloods that burn up fat continually at a basal rate, and can burn off more with aerobic exercise or any kind of exertion. For example, making your inland bearded dragon run around for a few hours every day will have some benefit in regards to fat burning and gaining of muscle mass, but it will be truly minimal, which is directly the opposite of what happens when endotherms are submitted to the same aerobic activities. 4/ Herbivores and insectivores (like our dragons) do not have digestive systems built to handle a large amount of calories from fat. Once digested, fat is either passed, or it's stored. Once stored, it can only be burnt off during what I can best describe as "starvation periods". Some degree of exercise will help but, as I said above, it's nowhere near comparable to a human or mammal. This means that once a certain level of fat is consumed over time, the body becomes 'overloaded' as it were, with no means to burn off the fat if the reptile is still being fed. Even if you cut the diet back to healthy greens and low-fat insects, because enough food is being consumed so that the dragon does not need to use its fat reserves, the damage from all that fat remains and grows over time. Issue #2: Which studies are more viable; those on herbivorous reptiles, or those on carnivores? As mentioned previously, most studies on fatty liver disease (and therefore the fat intake of reptiles) are based almost solely on obligate herbivores, such as the green iguana (iguana iguana), or obligate carnivores like the savannah monitor (V. exanthematicus). Which is more viable when we’re trying to discover the effects of high fat foods, such as rodents, on our bearded dragon? The answer, it seems, is in the anatomy of our dragons and those species that share a similar diet. The green iguana is most often studied in cases of fatty liver disease and is an obligate herbivore, meaning that it has specifically evolved to eat only plant matter. This has obviously resulted in a specialist digestive system that differs greatly when compared to that of a carnivore. Due to being so highly specialist, the study of the introduction of ‘foreign’ foods such as protein can produce interesting and educational results, leading to better insights in regards to captive husbandry (after all, it was not so very long ago that people assumed iguanas were omnivores that could happily eat monkey biscuits, insects, even canned dog food). The inland bearded dragon, by contrast, is most definitely an omnivore (or insectivore, as their primary protein needs come from insects). However, in the wild dragons eat a wealth of plant matter, so that it makes up 60-90% of their overall diet. Considering this, and looking at a dragon’s digestive system, one can safely assume that the inland bearded dragon’s digestive tract has evolved to be most similar to an obligate herbivore’s than to a carnivore’s. Due to a dragon’s high insect intake, particularly during youth when the protein is needed to support their incredible growth, it can be assumed that they have evolved to metabolise protein more effectively than obligate herbivores. The fact, however, that they eat primarily insects means that they have clear restrictions on just how much fat from protein they can process on a regular basis, as their body simply has not evolved to be used to such high loads, unlike a carnivore who has a body and metabolism specially adapted for processing high fat protein sources, such as rodents, rabbits, and other small mammals. Issue #3: But don’t dragons eat rodents into the wild? That proves that it’s safe to feed them. Although studying wild dragon behaviour gives us an insight into how we should care for them in captivity, the two are not directly comparable. In the wild, the chances of a dragon coming across easily caught rodents (usually young mice such as pink mice or ‘fuzzies’) regularly are statistically low. It's far more likely that they daily find insects and plant matter, hence why they have evolved to eat a diet consisting mostly of plants and bugs. Food intake “also varies with locality and time of year. Victorian herpetologist, Fred Rossignoli noted that most wild Pogona vitticeps seen by him seemed to have eaten mainly seeds. That observation was based on looking at their faeces. I have noticed that at certain times of year in some areas, that beetles feature prominently in their diet. These lizards are known to feed on flowers and other vegetable matter, yellow Dandelions being a frequently quoted item (e.g. Kennerson and Cochrane, 1981). Captives readily take cockroaches, crickets, mealworms, earthworms and other small animals. Small rodents are also taken”. Clearly rodents are part of the diet, as observed in this study, but it is also stated that the intake varies considerably and therefore we can assume that dragons only feast on such prey when the opportunity presents itself, which would be relatively rarely considering that dragons are only really large enough to kill and eat small, juvenile mice, and must compete both with other dragons, and larger predators that survive primarily on rodents as a food source. Dragons in the wild also live in a feast and famine environment, meaning that they can feasibly go an extremely long time between feedings. In fact, I'd theorise that one of the main reasons a relatively small lizard like the bearded dragon eats up to 90% plant matter as an adult in the wild is because it's the most reliable food source in their environment. Each day they can find it to eat, but pinkies and fuzzies will only be found on occasion. If a wild dragon eats a pinkie or fuzzy, it will therefore probably be weeks, even months, until it gets the chance to find and eat one again. Even if it ingests a number of pinkies in one feeding, it still is unlikely to do damage to itself because it will then go a very long time before eating mammalian protein once more. By going through this long period between feedings of such high fat sources it ensures that the fat will be utilised. In captivity, our dragons live much more sedentary lives. Reliably they are fed and we ensure that they get exactly what they need to be healthy. Under these regular feeding conditions, feeding pinkies and/or fuzzies every few weeks, maybe even months, increases the risk of overfeeding fat purely because your dragon will have little to no chance of burning that fat off, unless it is gravid reliably or regularly goes into brumation. Similarly, we can't say for sure how damaging it is for wild dragons to eat rodents because most do not die from issues such as fatty liver disease, but by predation, territorial disputes, egg laying, or parasites. If wild dragons aren't living to old age, we can't therefore ascertain with 100% accuracy that mammalian protein isn't harmful, since they never have the chance, or conditions, to over ingest it and therefore suffer from it. Similarly, we're not out collecting every wild dragon corpse, so there's only some degree to which we can definitely state why young and adult dragons die of disease, as opposed to predation. Therefore we look to captive reptiles to ascertain the viability of mammalian protein within a dragon's diet. Issue #4: Some people claim that their dragons didn’t become sick from fatty liver disease until months, even years, after it ceased to be fed high fat food. Is that possible? If dragons are fed just on high-fat foods like pinkies the damage has been done. It doesn't matter if it takes months to years for the symptoms to become evident as they are still caused by too much fat due to the nature of the disease. As explained above, dragons, as cold-blooded creatures, are not continually burning their fat stores for energy. Usually fat is only heavily utilised during periods of famine, lack of appetite due to health issues or gravidity, or brumation. This means that, even after being placed onto a healthy, low-fat diet, some dragons will still be dealing with the damage caused by overeating high fat prey items. With reptiles, their chance of improvement after being fed high fat foods is rather low and the recovery is slow. Many people have lost seemingly healthy rescue pets all of a sudden, only to have a necropsy performed to discover that it was fatty liver disease that indirectly killed them, even after years of a healthy, low-fat diet. Conclusion So what can one conclude from all of this? Is feeding rodents a valuable part of a dragon’s varied diet, or is it an undue risk to take? When is it appropriate to feed rodent prey items to our captive dragons? The only real answers come from individual feelings on the matter. If you have great success feeding your dragon rodents then that supports your choice. If, however, you are nervous about your dragons fat intake them it might be best to steer clear. The following are a list of basic pros and cons of feeding rodents to dragons: Pros -Rodents are an excellent source of calcium and protein due to their skeletons and high meat to skin ratio. -Young rodents, such as pinkies and fuzzies, are easy to digest due to their soft bones, thereby decreasing the risks of impaction from consuming such a large prey item. -Underweight and/or gravid females have responded very well to high protein, high fat prey items. It's my understanding that the reason pinkies are recommended for underweight gravid females is because their appetite can decrease to the point where the female refuses to eat at all, even long after the eggs have been laid. When you can coax her into eating, therefore, it makes sense to get a large dose of high-protein food into her all at once, rather than attempting over a long period of time to get her to eat insects/salads. It is basically a case of trying to get as much nutrition into her at one time rather than risking her going off food again as soon as she's had an insect or two. -They add variety to a mainly insectivorous diet. Cons -Too much fat is often the cause of problems such as fatty liver disease, which can lead to fatal health problems. -The fur of fuzzies have sometimes caused mild, to severe, impaction in herps, though this can largely be avoided by cutting a fuzzy in half and feeding each half as a separate portion. -Due to the manner in which dragons store their fat (primarily in the tail-base and abdominal cavity) obesity can cause impaction. As the large fat cells in the abdominal cavity fill, they restrict the space assigned to the stomach and other internal organs, which can lead to constipation and eventually fatal impaction. -It is unclear as to how much mammalian protein is safe to feed. -No one, as of yet, has a clear answer as to how often one should feed rodents to dragons, and considering that overfeeding could possibly lead to fatty liver disease or similar problems due to excessive fat consumption and build up, this is an unsettling risk to take, and one that should be considered very careful by the individual owner. Considering all of the above, my personal conclusion is that there is no really conclusive evidence in regards to the inland bearded dragon’s ability to metabolise and digest high fat containing prey items, such as rodents. However, what we do know seems to point to them being more similar to herbivores than carnivores, both in digestive tract structure and metabolic rate. Therefore it seems wise to very carefully monitor just how much protein your dragon has access to; including that obtained from their primary prey source of insects. In my personal opinion, I’d recommend avoiding rodents altogether. If you feel your dragon might benefit from mammalian protein then I’d suggest feeding fuzzies over pinkies. Pinkies are largely just fat, whereas fuzzies are lower in fat, higher in protein, and still small enough for an adult dragon to consume (though cutting it up to reduce the chances of choking is advised). Similarly, I’d personally recommend feeding mammalian protein sparingly, maybe once every few months or even a year, unless your dragon regularly brumates, or becomes weak during laying. It seems to me that the above is the safest compromise, but as always it’s your choice as a responsible herp owner to decide what is best for your individual dragon. * Sources cited: Hoser, R., “Pogona; From an Australian Perspective”, Reptilian Magazine (UK), 1997. Web link: http://www.smuggled.com/pogona1.htm Kaplan, M., “Animal Protein and Green Iguanas”, 2001. Web link: http://www.anapsid.org/iguana/animalprotein.html King, K., “Bearded Dragon Gross Anatomy”, 2005. Web link: http://mrskingsbioweb.com/beardeddragngrossanatomy.htm Mader, D., DVM. “Hepalipidosis; the best cure is prevention”, Reptile Magazine, 1999. Web link: http://www.anapsid.org/heplipidosis.html General and specific information on endo- and ecto-therms: http://dml.cmnh.org/1998May/msg00072.html http://vilenski.org/science/safari/classifyall/endoecto.html http://www.science.widener.edu/~grant/cour...n6_answers.html For an excellent diagram of the green iguana’s digestive system, see the following web link: http://physrev.physiology.org/cgi/content/full/78/2/393/F2
I think it's an excellent resource. I agree that there hasn't been a whole lot of research, but we can take it on a case to case. I have always tole ppl that pinkies are for rescues and gravid females. Even then, only once a month due to high fat. There is no need for pinkies in any other situations. Either the beardie is too young [and small] to digest such a big meal propertly or the adults have no need for so much fat/protein because they are no longer growing. -Sara
