Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Adam Britton: Animal Protein and Claw Trimming

©1996, 2002 Adam Britton


A Note from Melissa Kaplan... The server that normally houses Adam Britton, PhD's site is erratic. Until he leaves the Australian outback and can get to a place where he can move to a more reliable server, I am temporarily housing his Animal Protein Issues, Claw Trimming, and About Adam Britton articles here at my site.

Animal Protein
Trying to find accurate information about green iguanas is often like trying to discover whether UFOs really exist. But, as the saying goes, the truth is out there - if you look carefully enough. Here are my opinions on the controversial matter of whether green iguanas should be fed animal protein in their diets - and that includes high plant protein sources such as soybean or tofu.

I'm a zoologist, and I've been doing some research on iguana diets in recent years. One thing you realise when you look at the literature and talk to animal nutritionists is that we still know so little about iguana physiology that we're basically drawing our conclusions from other animal physiology, filling in gaps ourselves, and coming up with a good guess. Here are some of the main pros and cons as far as I see the whole issue.

Iguanas have evolved to fill a certain niche - that is, herbivory in arboreal tropical environments. They are successful, because there are few competitors (especially reptilian ones). This pressure to efficiently digest plant matter has led to a longer, more sophisticated digestive system to enable fermentation and breakdown of otherwise quite hard to deal with matter. However, the pressure has been there because of the abundance of food, and perhaps the lower energy requirements necessary to locate and acquire food sources. Take a pinch of salt, add several hundred thousand years, and you have a digestive system nicely adapted for herbivory (I won't say perfectly adapted, because perfection is a very subjective quality!).

None of the published scientific field research on green iguana diets in the wild suggests that they take animal protein, but it does show that they derive all their protein (and other) requirements from plant materials in the diet. Anecdotal reports which seem to have made it into the literature suggest that juveniles have an increased propensity to take insects. There is the odd report that iguanas also take bird eggs and carrion - there's even less evidence for either of these. The nutritional research which has been done (examining wild iguana gut contents) shows no evidence of animal protein, although if it were present it would be in such low amounts so as not to be detected by such a study. So, the natural diet of green iguanas does not include any animal protein. This doesn't discount the notion that they might accidentally ingest the odd insect together with a flower head, or whatever, but I hardly consider this to be anything significant... in the same way that cows don't eat animal protein, but they're not going to wrinkle their nose and lightly brush stray bugs from their juicy grass stems. My conclusion here is that they are strict herbivores under normal circumstances.

Take a look at iguana morphology and physiology. Iguanas are not equipped to hunt down and digest animal prey. Their digestive system employs a hindgut fermentation process, which is to break down plant matter, cell walls and carbohydrate. This isn't to say they couldn't digest animal protein, but just that they're optimised for plant matter. They also spend their entire time in the wild living on their food plants. Why spend time and energy hunting animals when plant food is all around them? So, my conclusion that they are strict herbivores still stands.

Feral green iguanas (e.g. Puerto Rico) have been reported to take insects more frequently that "incidental" would imply. Captive iguanas will also readily take insects, mice and other sources of animal protein if offered them (mice are often taken by iguanas that would happily remove your finger at the same time - almost giving the impression that they would eat anything presented to them). Some people seem to have almost converted their iguanas into carnivores. However, iguanas are nothing if not opportunistic. It seems that under conditions of stress and poor food availability (and that includes feral populations, which are mal-adapted to the local flora), they will resort to using additional food sources until the situation improves. This suggests that even in their native habitat they might resort to limited omnivory if that becomes necessary for survival. Iguanas in captivity are nothing if not stressed, and offered poor quality diets on the whole. Therefore, eating insects, mice or whatever doesn't seem unreasonable. Iguanas will happily eat their substrate if nothing else presents itself. Herbivorous animals have been known to eat carrion, including their own kind, when presented with no other food sources (e.g. cows and sheep have been reported to do this). Given this evidence, though, it seems that eating animal protein is a "last resort" - i.e. it's a poorer choice of diet. Also, in the wild, if a normally herbivorous iguana is forced to resort to eating some animal protein, the change will be temporary until better food options present themselves.

Iguanas, and any animals for that matter, grow very quickly with increased amounts of protein. If you're interested in fast growth rates, usually when the animals are harvested for food, then increase their protein intake. As animal protein is better than plant protein for this, then feeding herbivorous animals animal protein will increase growth rate. This is why there is so much controversy over BSE in cows in the UK - beef cattle are pumped full of animal protein (including spinal tissue, in this case) so they grow quickly. However, the farmer is not interested in long-term health - the animals are culled at an early age, with the exception of breeding animals which receive a different diet anyway. Dairy cattle are fed lower amounts of animal protein. Long term health is affected by excess protein, however. Veterinary evidence shows that excess animal protein in iguanas leads to gout, dehydration, metabolic bone disease, renal failure, kidney stones etc... and is one of the biggest causes of relatively young iguana mortality. The reason these poor diets (i.e. high percentages of animal protein) exist in the older literature is that they were formulated from farm-raising practises of green iguanas. So, iguanas show good growth rates, but the longterm effects severely shorten longevity.

Animal protein contains components which iguana digestive physiology can't deal with in large amounts (e.g. fats, different purine/pyramidine ratios, different amino acid ratios). This also very likely unbalances the natural gut fauna the iguana possesses in the hindgut (as has been shown in studies on other herbivores), reducing digestion efficiency of plant matter which should make up the majority of the diet anyway. Iguanas, being herbivores, are physiologically adapted to process specific kinds of dietary protein - i.e. those found in plant materials. While animal protein can be metabolised, it literally overwhelms the system in excess (and it doesn't take much to cause an excess - although we don't know exactly how much). Nucleic acids in the foods are degraded to nucleotides and ultimately pyrimidine and purine bases - more are synthesised from amino acids in the liver. Any of these which are not used by the body are broken down into uric acid (or allantoin in some mammals, reptiles, fish). With animal proteins, green iguanas end up with an excess of uric acid in the body fluids, and over time this crystallises out - so uric acid crystals form in tissues throughout the body, impairing their function and leading to serious problems.

There's no doubt that excess animal protein kills iguanas in the longterm. However, that's not the question. The question is, is there a certain amount of animal protein (very low percentage of daily intake) which will either not harm the animal, or perhaps even be beneficial because of its high protein content? Hindgut fermentation works best in larger animals (more efficient per unit volume of food), but what about hatchling iguanas which are much smaller? Would perhaps the odd insect lead to increased growth with no obvious health problems until the hindgut area grew large enough to be able to reach a greater operating efficiency? (i.e. they're not utilising all the purines/pyramidines in their diet, so animal protein doesn't cause uric acid concentrations in the blood to go up significantly because not all the purines/pyramidines are being utilised)

It is quite commonly believed that animal protein is the only way an iguana can get any or enough calcium in it's diet (because animal bones contain calcium). This is incorrect - calcium is present in varying quantities in most plants, but still many iguanas suffer from calcium deficiency which leads to metabolic bone disease. In order to prevent these symptoms, a balanced diet needs to be created which contains sufficient calcium and sufficient vitamin D3 (which may be present in the diet, supplements, or more usefully through synthesis in the skin by the action of UVB wavelengths in sunlight). At the same time, the inhibiting effects on calcium metabolism of phytates, oxalates, acid and fat must be minimised. Powdered calcium powder helps to supplement a diet which might otherwise be low in this important element. It is also sometimes believed that animal protein is the only way an iguana can get any protein, period! This simply isn't true - plants also contain proteins, but with different ratios of amino acids to animal tissue (the former of which the iguana digestive system has evolved to cope with).

Ranging from Mexico to Brazil as they do, iguanas come from a diverse array of habitat types and it's very likely, given the morphological and behavioural variations that exist, that similar variations in dietary preferences also exist. Perhaps some populations do select limited amounts of animal protein, and perhaps these animals do have lower life expectancies. We simply don't know this yet. There are clues: some iguanas appear to reach much smaller adult sizes than their counterparts. It's one of my speculations that these animals may be adapted to a poorer diet (caused by adaptation to the different foods available in another habitat), and even if presented with a richer diet don't grow as quickly as those from other populations. Although Iguana iguana is one species, there are many different races which can often become available in the pet trade. Remember, though, that captive farmed iguanas (which make up by far the majority of animals available) are coming from a limited number of breeding operations, which are harvesting eggs/raising animals from the same area, and therefore diversity in captive populations may be more limited. I'm a little wary, though, of suggesting a perfect diet for all iguanas (from Mexico to Brazil) - it doesn't make any sense that they would all benefit equally from exactly the same diet given that they don't live in the same environments, but until we learn more (and we haven't yet) the best we can do it provide diets which we know are beneficial to the widest number of animals.

Iguanas are herbivores. However, like adding leaded fuel to an unleaded car, you can still throw other things through the digestive system, and it will still try and do what digestive systems are good at - digest it! A small amount of leaded in an unleaded car might make it hiccup at little, but no lasting harm. In captivity, though, people put too much leaded fuel in and destroy the engine of their iguana over time. The whole digestive system can cope with much of the contents of animal protein, but because the rest of the body isn't used to dealing with this kind of food source (inc. high protein, fat etc...), things get thrown out of balance if there's too much of it (this doesn't normally happen under natural conditions, otherwise selection pressure would tend to lead to more omnivorous animals).

Those who think that green iguanas should for some reason be fed animal protein are not considering their natural physiology or behaviour. They know that animal protein (i.e. large amounts of protein) will result in additional growth. They're right - just look at beef cattle. However, much of this information has come from captive farming operations where animals were intentionally grown quickly for either reintroduction programs or for food purposes. In the former, the longterm negative effects were not known, although if it was enough to allow several breeding generations of wild animals then its purpose would have been satisfied. In the latter, who cares if an animal will die at 5 years if it's slaughtered for lots of meat at 3 years?

Interestingly, many of those formulating diets for captive iguanas for the pet industry still include animal protein, because there's a belief that there must be some level at which animal protein benefits growth without significantly affecting longterm health. I think this view is erroneous, particularly as they still have little idea what kind of protein levels are harmful - taking a chance, if you like, but if the food makes your ig grow, people are going to buy it, right? Perhaps this is a factor - if someone buys product A that includes animal protein, their iguana will appear to grow faster. But, if they try product B because they hear it has no animal protein, but their iguana's growth slows down a little, they might go back to product A. Cynical, but probably not without merit! If someone does decent longterm research and proves my view wrong, then fine, but until they do my opinion stands. After all, a good artificial diet is theoretically possible.

My overall conclusion to this is that no, we don't know it all. Far from it. However, everything that we do know so far tells us to be very cautious. I'm sure the odd bit of chicken, insect or whatever on very rare occasions will do the iguana no harm. However, I really don't see why this should be necessary, and I can't understand the hangups about missing it out altogether. It's almost as though people feel that iguanas must have a little animal protein every so often, otherwise they might be missing out on something. I get the impression others tout animal protein just because everyone else says don't bother with it. When the idea of using animal protein is so entwined within the literature of even fairly modern books, it's hard to avoid this question - it keeps coming up time and time again. This is good, because every time it comes up, we hopefully know a little more about how the processes work. At the moment, however, we don't know enough, and so my advice to people is always not to include it - not because a tiny bit might not be beneficial, but because too much is definitely bad, and we don't know how much is too much! People who use animal protein are, in my opinion, playing dice with the health of their iguana (longterm), and I don't think it's worth it - given that we know a totally herbivorous diet is very healthy - but a good totally herbivorous diet, that is! A bad diet, period, will kill your iguana. But I think the best diet is totally herbivorous, until I see any convincing evidence to the contrary, or firm data to show how much animal protein can be safely utilised (if any).


Donoghue, S. (1996). Nutrition of the Green Iguana (Iguana iguana). In: Proceedings of the Third Annual Conference of the Association of the Reptilian and Amphibian Veterinarians (Frahm, M.W. ed.). ARAV. pp. 99-106

Donoghue, S. & Langenberg, J. (1996). Nutrition. In: Reptile Medicine and Surgery (Mader, D.R. ed.). W.B. Saunders Company, Philadelphia. Pp. 148-174

Marken Lichtenbelt, W.D. van. (1993). Optimal foraging of a herbivorous lizard, the green iguana, in a seasonal environment. Oecologia 95: 246-256

Rand, A.S., Dugan, B.A., Monteza, H. & Vianda, D. (1990). The diet of a generalized folivore: Iguana iguana in Panama. J. Herpetol. 24: 211-214

Van Devender, W. (1982). Growth and ecology of spiny-tailed and green iguanas in Costa Rica, with comments on the evolution of herbivory and large body size. In: Iguanas of the World: their Behaviour, Ecology & Conservation (Burghardt, G.M. & Rand, AS, eds.), Noyes Publ., Park Ridge, N.J. pp. 162-183

Claw Trimming
Contrary to popular belief, iguana claws can be trimmed easily without pain or bleeding if you take the time and care to do it right. This page describes how to trim claws properly, and provides a diagram to assist you.

Anyone who keeps green iguanas (Iguana iguana) cannot fail to be impressed by the way they look. Their dorsal spines, dewlap, tail and long claw-tipped toes all contribute to their unique appearance. In their natural habitat, these physical characteristics play important roles in their social displays, their natural behaviour, and in their camouflage and defence. When we keep one of these demanding reptiles in captivity, however, we need to be aware of what iguanas use these morphological adaptations for, because it will influence the ways in which we house them and care for them.

One of the most obvious of these physical adaptations is the presence of the powerful legs, the long toes, and the sharp, curved claws. In the wild, the iguana uses these superbly when walking, running, climbing and leaping. The legs can propel them at surprising speed both along the ground and up trees - something of which you need to be aware if you want to give your iguana a little more freedom. The long toes and sharp claws are used primarily in climbing both up and down branches and trees - they act almost like grappling hooks, or spiked climbing shoes, providing a strong grip on otherwise potentially slippery surfaces. A fall from a great height could result in disaster for an iguana.

Claws in Captivity
The problem with an animal which possesses sharp claws will become apparent to anyone who tries to pick one up. Whether intentionally or not, a swift and determined movement of the foot can result in quite deep scratches along your arm. In the wild, this is part of an iguana's defence mechanism. An animal bitten, scratched and whipped will be much more likely to look for an easier item to add to its menu. If you're keeping an iguana in captivity, however, you need to consider the potential effects of their sharp claws. Handling your iguana on a regular basis is an important part of interacting with it if your intentions are to tame it. In addition, regular handling is also important if you want to move the animal around - for example, when you need to clean the enclosure. In such a situation, you don't want to receive deep scratches each time you attempt to pick the iguana up. Apart from their unsightly appearance, cuts and scratches are a potential source of infection, especially if the claws harbour dirt on the underside - not unusual, as the underside of the claw tip is grooved. There are other disadvantages to your iguana having long claws, and these will be discussed later.

What about age? Should small juveniles have their claws trimmed? It's certainly a good idea to start early - that way you have more chance of getting the iguana used to the routine of claw trimming. More care must be exercised, however. Juveniles have much smaller claws which are less well-defined than those of older iguanas, and otiose easier to make a mistake. In this case, it may be easier to use a smooth file on the claws, as this minimises any risk of injury, and very little actual claw tip needs to be removed. Once they get used to you messing with their claws (which also gives you the opportunity to check for unshed scales or caught fibres), they're more likely to co-operate when they get larger - and they do get larger very quickly if you're looking after them properly!

Trimming Iguana Claws
The important thing to remember when trimming (and I use this word instead of cutting for a good reason) claws is not to overdo it. The word trimming implies removing just a small amount of claw, and this is exactly what you need to do.

Diagram of iguana claw, by Adam Britton


Figure 1 shows a drawing of an iguana claw viewed from the side. If you hold your iguana's claws up to the light, you should be able to see this. You can see that the claw is composed of two main sections. Where the claw meets the scales of the toes, it contains blood vessels and nerves - this is the growing part of the claw, and should definitely not be cut. Doing so will cause a lot of pain to the iguana, together with a lot of blood, and will become a potential site for infection. Imagine cutting your nails right down into the quick - even removing the tip of your finger! This is what it would be like for the iguana if you cut this section of the claw.

The second part of the claw is the sharp, curved tip. The top of the claw grows at a faster rate than the lower part, which is why it curves downwards. The claw tip contains no blood vessels or nerves - it is dead, just like the tips of your fingernails. This is the part of the claw you need to cut. It's best to use a pair of small dog claw trimmers for this - human nail scissors or clippers are not designed for cylindrical claws like an iguana's, and tend to crush and damage the claw. But how much do you cut off? It's a good idea to cut no more than half of the claw tip off (see dotted line on diagram). Not only does this reduce the chance of you making a mistake and cutting into the living part of the claw, but it's also better for your iguana. If you remove too much, your iguana will have very blunt claws, particularly if you file and smooth the end. While this may seem better for you, with less chance of being scratched, it's a poor deal for the iguana which uses its claws during climbing and may therefore be unable to move around in its enclosure properly. Blunt claws increase the chance of the iguana slipping, especially on branches, and therefore injuring itself. Cutting off no more than half of the tip will ensure that its claws are still sharp enough to be effective, but not so sharp that it makes handling your iguana a hazardous experience.

Iguanas often don't like having their claws trimmed, although they get used to regular routines - once every two to three weeks if you trim less than half of the claw tip. My iguana has come to accept it as "one of those things" and looks at me as if to say "Go on then, if you really must." An irregular routine will only be stressful for the animal. If you can, try and get someone else to hold the iguana, preferably in a soft towel, while you do the trimming. Holding the appropriate leg is also a good idea, otherwise sudden movements increase the risk of you making a mistake. If you simply can't get someone else to help, then there are other solutions, such as trimming claws after the iguana has fallen asleep each night. Don't try and rush through the job - be slow and methodical, dealing with claws in the same order each time.

Once the claw has been trimmed, make sure the end is clean and tidy. Split claws will trap dirt, which may be transferred to your skin if you're scratched. If you do make a mistake and cut into the living claw, make sure you clean the tip of the claw with a sterile swab. The wound should stop bleeding quickly, but specific products available from your vet can be used to stem the flow of blood more rapidly.

Is Trimming Really Necessary?
Trimming claws on a regular basis is a necessary care requirement when keeping a green iguana in captivity for a number of reasons. I've already mentioned the disadvantages to the handler if the iguana's claws are very sharp. One of the commonest reasons people "give up"on their green iguanas is because they become vicious and aggressive when handled. Taming iguanas requires regular handling, and this can be achieved much more easily if the claws don't inflict painful and visible wounds every time the animal is picked up. Wearing gloves and long-sleeved tops can overcome this, but gloves should not be necessary from a handling standpoint - in fact, gloves can make it difficult to determine how hard an iguana is being held, which could result in injuries to the iguana through over-enthusiastic handling. Injuries through scratches can also lead to secondary infections in some cases, and claw trimming will help to avoid this.

Another reason for trimming is to benefit the iguanas. In the wild, iguanas tend to do more climbing, running and leaping over a variety of different surfaces than they do in captivity. This provides plenty of opportunities for the claws to be worn down naturally. Captive iguanas which do not have their claws trimmed can eventually develop problems, whereby claws can become too long and curve back on themselves, even injuring the iguana or others in the same habitat as they climb about. As the iguana's caretaker, it should be your responsibility to keep your iguana in peak condition, and regular claw trimming should be one of the many ways in which you achieve this.

About Adam Britton...
Wong's Green Iguana Heaven was created by Dr. Adam Britton, a professional zoologist currently working on population ecology and behaviour in crocodiles, together with feeding ecology in insectivorous bats. His interests extend into many fields, however, one of which is a longterm involvement in green iguana biology, ecology and captive husbandry. He is principle author of the video "Captive Care of the Green Iguana" (produced by Scimitar Film Productions). This project is part of his desire to see the internet used as a resource of information which is both interesting and accurate.

Need to update a veterinary or herp society/rescue listing?

Can't find a vet on my site? Check out these other sites.

Amphibians Conservation Health Lizards Resources
Behavior Crocodilians Herpetology Parent/Teacher Snakes
Captivity Education Humor Pet Trade Societies/Rescues
Chelonians Food/Feeding Invertebrates Plants Using Internet
Clean/Disinfect Green Iguanas & Cyclura Kids Prey Veterinarians
Home About Melissa Kaplan CND Lyme Disease Zoonoses
Help Support This Site   Emergency Preparedness

Brought to you thanks to the good folks at Veterinary Information Network, Inc.

© 1994-2014 Melissa Kaplan or as otherwise noted by other authors of articles on this site