Diet considerations

[Odonata]

I have done a lot of research on this subject online, and there is a surprisingly broad set of beliefs (since most of it is not well scientifically supported I don't think it can be considered anything else). Different sites claim to describe dietary requirements in great detail and with often different information. This post is not meant to bring up old discussions/arguments about the natural diet of tegus. It is clear that tegus are highly adaptive, in fact I like the comparison with squirrels that I saw somewhere recently. The implication being that they can indeed proliferate as a species far from their origin in terms of diet and habitat.

However much like humans, just because squirrels and tegus can live on junk food, it does not imply that it is the best diet to support their nutritional needs. I recently visited our local exotic animal vet, who as an aside is quite a character! (breeds and trains birds of prey and other animals for movies, actually discovered new specimens in the Amazon, etc). He is very knowledgeable from an experience standpoint, and is usually spot on with any advice. We got to talking about tegu diet, and I mentioned the common themes you see online that suggest feeding, fruit and vegetables, and cooking eggs, etc. He laughed and said it was another case of the internet propagating inaccurate information. His main comment being that tegus are unable to digest vegetable matter that is raw which is why they do not eat it in the wild, it puts a strain on their digestive system and provides no value (I realize there is an argument that fiber is important, which is hard to say, and makes some sense, but eating rocks could provide the same benefit). Fruit also has no real nutritional value. Whole prey, from eggs and young to anything they can take down making up the majority of their diet. Obviously nothing is cooked in the wild. That you can cook something and have a tegu eat it is not the point, they have evolved to eat raw foods and all of the bacteria that comes with that. They will eat carrion and scavenge from other predators. Interestingly the vet felt that the eating of whole prey actually provided vegetative matter that was partially digested in the animals intestines, and that is why the intestines specifically will often be eaten in prey that cannot be consumed whole (never seen that documented anywhere, interesting I thought). He commented that this was the only way that tegus could ingest vegetable matter that could then be absorbed. Again without sufficient scientific study this is just food for thought.

I do think that new owners should consider information carefully before believing that anyone providing definitive information has any real basis for doing so. The reptile world seems to reflect the world we all live in. There are all too many examples of obese reptiles that their owners think are happy and content, that will live shorter lives. Obesity being one of the visible symptoms of improper nutrition, many other reptiles will die in captivity from a plethora of other deficiencies. I am not sure any of us should have captive animals, but given that we enjoy keeping them (myself obviously included), I believe we have a responsibility to be the best keepers that we can, and take the charge seriously.

 

[Roadkill]

Clearly this vet has read ZERO papers on the gut contents of wild tegus or observations of tegus eating in the wild. They all state that tegus eat a rather huge abundance of vegetative material, more so than is commonly given to tegus in captivity. Even those of focus on Colombian tegus indicate a surprising degree of vegetative matter for an animal that is often assumed to be exclusively carnivorous.

 

[Odonata]

That is likely the case. I haven't seen a great deal of scientific papers that have reasonable sampling sizes, and certainly not performed at different seasonal times to determine if there are seasonal patterns to support preparation for breeding, hibernation, etc. The paper that makes the rounds regularly and is oft cited being:

FWC BIOPROFILE FOR THE ARGENTINE BLACK
AND WHITE TEGU (Tupinambis merianae) Sept 2006

It does indeed support that adult tegus gut content included 66.6% plant material in a sample size of 70.

It doesn't appear that any cooked eggs were evident however

Great read for any that have not seen it before btw.

 

[TegusRawsome80]

Okay, my problem with the one study I have seen on it(the commonly quoted one I believe) is that all the tegus were collected from one specific area and it wasn't a huge number of animals collected and examined. That's not a conclusive study of tegus in general, it's a study of a population of tegus. As opportunistic feeders, I don't doubt that if more plant matter was available than whole prey they would eat more plant matter than whole prey. However, I have yet to see a study to actually convince me that they eat mostly plant matter. I do think the vet must be extremely uneducated if he thinks they don't eat any plant matter in the wild. I personally feed whole prey items and plants/fruits almost exclusively and don't feed the crap(ground turkey, eggs, etc.) that people who don't want to pay for quality food do.

 

[Roadkill]

The issue with eggs is that the yolk is a good source of biotin (a necessary micronutrient) but the egg white is high in avidin (which strongly binds to biotin and renders it unavailable for absorption). Heat readily denatures avidin. Hence the cooking. Before, someone had advised to use fertilized eggs to avoid this issue (I believe this was started by a vet) - however this is misinformation. The egg white component of the whole egg (where the avidin is) is added to the egg AFTER fertilization takes place with the egg cell, and the avidin gets used up as the foetus develops. So unless you are offering your animals balut (ie. eggs with chicks inside) then even if they are fertilized, they will contain substantial avidin.

With respect to vegetative matter, studies have shown (admittedly not directly in tegus) that omnivorous animals regularly fed vegetative matter in their diet have increased biotin uptake (beyond that which would be accounted for simply by the biotin content in the vegetative matter offered) than cohorts that are only fed vegetative matter sporadically. Think of it like exercise - regularly doing it has great benefit, doing it once in a while basically succeeds in making you uncomfortable.

As for the claim that they are unable to digest vegetative matter - I know there are studies that show reptiles are unable to digest high, complex starch content matter (ie. grains, corn, potatoe, rice) and that these lead to fermentation within the GI tract (think lactose intollerance, same effect). There is NOTHING out there that supports the claim that tegus cannot digest any vegetative matter. An interesting correlation, when you think about it, is those tegus that hibernate longer (those further in the south, such as Salvator rufescens) have shown in the wild a much greater vegetative content to their diet than those in the north which are very sporadic with their vegetative intake (Tupinambis teguixin) and that according to compatriots of mine doing metabolic studies in hibernating tegus, the predominant signs of energy usage in certain regions (one being the brain, responsible for coordinating it all) are carbohydrates.....there's something to think about in this.

The notion that fruits have no nutritional value - acerola is supposedly the highest concentration of vitamin C known to man in vegetative matter, açai is remarked on having some of the highest content of anti-oxidants in all fruits, jaboticaba is also known to be a good source of anti-oxidants as well as being anti-inflammatory and known to aid in respiratory issues, pitanga is known to be rich in vitamin C, calcium, iron, riboflavin and niacin, as well as being an excellent source of vitamin A - these are all fruits I've personally seen tegus regularly consume in Brasil. Anyone spouting that fruit has no nutritional value is making nonsensical claims, period.

Many of the statements you've presented are some that I've seen before, from Bobby Hill - don't know if you or your vet is parroting his stuff. Bobby Hill is about as knowledgeable about physiology and biology in general as I am about quantum mechanics: enough to convince someone who knows far less that we know what we're talking about, but really should keep our ideas to ourselves because we don't really know anything. Bobby liked to conjecture and make up stuff to convince people he was an expert. In reality, he's spread more myth than anyone I know with regards to tegus. This forum would do well to consider deleting most of his 'tags' and start from scratch.

 

[TegusRawsome80]

Roadkill, do you have any studies that take into account broader areas? Just curious as I'm always trying to further educate myself on their diets. What would you suggest feeding captive tegus and in what amounts?

 

[Odonata]

Just to be clear, I am not making statements to sway anyone's opinion whatsoever, and I am certainly not making any claim to be knowledgeable in this area as my interest in reptiles is relatively new. I do however have an inquisitive mind. I was mostly relaying a recent source of information that I found interesting, and pointing out that the internet is unfortunately full of information (not all of it good, accurate, or even relevant). That the internet exists as a source of information is indeed a great benefit to research. It used to be that significant time and travel was required to surface historical data, and studies performed by non-mainstream institutions/individuals (I am not talking about Tegus now), such that it could take years to collect sufficient data to submit a paper. Now it is fortunately much easier. However the issues with ensuring the validity of information, source, copyright, and other legal issues make it challenging in other ways.

Roadkill - I appreciate the information you are providing and find that very interesting. Do you have links to any recent studies in this area? I have more of a physics background, but due to my interests find this all quite fascinating!

 

[Bubblz Calhoun]

I couldn't agree with that more Roadkill, since they are opportunistic omnivores not carnivores (which is more commonly said and believed) people should feed them more of a variety. If they were meant to be carnivores or vegetarians then they would be.

 

[Roadkill]

Odonata, I hope you haven't been taking anything I've been posting as "chastisement", I tend to be blunt (and I'm at work and not supposed to be writing about tegus when I should be writing about mice and rats) and my messages can sometimes seem... harsh. What I want is for people to think. With respect to the internet, it is the most powerful tool mankind has come up with, and like most tools, there is a proper way to use it, and a dangerous way to use it. The internet is a great place to start your search, an absolute terrible place to stop. Anyone can put anything on the internet. I WISH, oh how I wish, I could provide links to the studies I'm aware of - unfortunately most either don't exist on the internet or you have to have an expensive account to look at them. Given time, I could dig up some references, but you'd still have to track them down through some educational institution, most likely. Unfortunately, Odonata, tracking down VALUABLE AND FACTUAL information STILL requires effort - both in getting the information in the first place, and then in effort to actually understand it. The peer review process isn't set up for scientists to be elitist and self-supporting, it is set up with the idea for other knowledgeable parties to see the holes and errors in peoples papers, much like what I try to accomplish here.

TeguRawesome, you have a very good point - many studies are not that broadly encompassing. Any gut content analyses I'm aware of will only be in localized areas, these will be different between studies, but still only represent snapshots of small areas, small time. However, the value in these studies is it is at least an informed starting point, something to build from. I've never understood the mindset that many have - they'd rather believe in extraordinary claims (fruits have no nutritional value) than try to listen and understand facts that, although not all encompassing, are still facts (ok, so if fruits are non-nutritional, why is it nutritionists recommend so much daily intake of them? Are they soley concerned with my ability to be regular?) It boggles my mind.

Bubblz, once again we are very much in agreement - I said much the same to someone the other day while I was showing them my tegus - people think of them as carnivores, when really they are opportunistic omnivores.

I'll offer this anecdote, and fully admit it is only anecdotal: after my first season in Brasil, the facility director came up to me to ask me what I was feeding my research tegus, because he had been checking them and comparing them to the rest of the tegus, and in his eyes, my tegus were in far, far superior condition than the stock they had come from. Before I came along, their diet was pretty much chicks, chicken head&necks, rodents, insects and the fruit that fell into the pens from the trees. Basically, I offered the same with vegetative matter added in. I was then given the whole tegu stock to care for. Furthermore, I'll add a further anecdote: I regularly give my tegus vegetative matter in their food. None of that vegetative matter is recognizable coming out the other end as vegetative matter. Therefore it is indeed digestible by tegus. Rodents, on the other hand, often do have components come out the other end of the tegus that are quite identifiable.

 

[dragonmetalhead]

Anyone got any links to feeding studies on Colombian tegus specifically? Most of the info I find pertains to Argentines.