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.
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!).
RESEARCH ON WILD
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.
ADAPTATIONS TO HERBIVORY
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.
EXCEPTIONS TO THE
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.
HIGH PROTEIN INTAKE
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.
OF ANIMAL PROTEIN ON IGUANAS
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.
DO SAFE LEVELS EXIST?
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)
BUT ISN'T ANIMAL
PROTEIN REQUIRED FOR...?
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).
ON NATURAL VARIATION
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?
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
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
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
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!
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.
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
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
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