Note - I received this from Melissa Kaplan via e-mail some time ago. Since that time, she has published http://www.anapsid.org/comfood.html and http://www.anapsid.org/evalcomm.html However, I think the information in this e-mail is still helpful.
By Melissa Kaplan
In the past decade, the imports of green iguanas have jumped from 136,000 a year to over 1,000 ,000 last year. Five years ago, there were no commercial iguana foods on the market. Four years ago, the pink glop found its way onto pet store shelves. Three years ago saw a veritable smorgesbord of commercial foods--dry, canned and frozen; dusty, herb-y, pelleted, granularized and mushy--hitting the stores. All of these foods have three things in common:
With the newfound understanding of the effects of the fresh food diets that have been recommended for the past 10 years or so, including listing foods known--for at least the past 5 years--to be detrimental to the iguana's long term health, [such as whole prey, cat foods, high quantities of dog foods, monkey chow, low nutrient foods (such as tomatoes, zucchini, cucumbers, and lettuces, including green and red leaf and romaine) and foods which iguanas have no capability to digest (dairy products), high oxalate foods (such as spinach), goitrogenic foods (broccoli, Brussels sprouts) and frozen foods, and high purine foods (asparagus, whole grain cereals, cauliflower, beans and peas, spinach, mushrooms and wheat germ], and with balanced fresh foods diets easily prepared at home, there is no reason to use old food lists, or to feed the commercial foods - certainly not the way the instructions on the labels read (most of them state to feed ONLY the commercial food, not any fresh foods other than to make the dry stuff palatable in the beginning, and to feed the foods dry).
Anecdotally, I have seen and heard of iguanas developing metabolic bone disease after being fed some of the commercial foods for a year. Other adverse effects include lethargy and slowed growth (one food causes rapid growth - but ultimately it too causes MBD). For obvious reasons, none of the companies which make the foods are going to fund studies into which food is better or which foods are bad - the latter, after all, may be theirs, and the former may be a competitors. (Pretty Pets backed out of one such study in the UK.) One independent study in the US by a reptile vet/nutritionist which compared three highly touted commercial iguana foods with a proper fresh foods diet found that the commercial foods were significantly less than they were cracked up to be, with the 'best' of them being too high in protein and formulated based the research to grow iguanas quickly for human food consumption; this is the same food which causes MBD within a year in captive iguanas (including Cyclura iguanas in a breeding project in their native environment, being kept out of doors) - and it also contains animal protein. The best recommendation, then, would be to listen to what the experienced and trained reptile vets are finding (kidney failure, liver problems, clogged arteries, MBD), the growing results of feeding properly constructed plant-based diets on growth and overall health (again anecdotal, but strong), and the experiences of those working on iguana breeding programs - not for the pet trade, but with endangered species and for breeding (the aforementioned Cyclura iguanas included).
There is another concern with feeding these dry foods as directed on the package. Increasingly, reptile vets in the US and the UK are convinced that the high rate of kidney failure may also be attributed to iguanas being kept in environments that are much drier than they experience in the wild. Feeding animal protein and dry foods puts major strain on the body's fluid volume as it rushes to try to process this ingesta through the digestive system (with animal protein, the purines are also at fault) thus these dry foods, even with the iguana apparently drinking its fill and sprayed or bathed occasionally, the animal remains in a state of chronic low levels of dehydration.
Just remember: if it were easy to keep exotics, far fewer would die each year, and far fewer would be abandoned or given away sick, injured and, in the case of many such as the iguana, still untamed. One of the challenges of keeping (or, to be more accurate, to be kept by) an exotic is to do it right, right enough that the animal lives its full natural lifespan and reproduces freely in captivity. It should be noted that the people in the US and England who are breeding green iguanas successfully, including the founder of the International Iguana Society, are doing it on fresh foods diets, not commercial foods (despite the quantities off commercial foods shipped to them every year by manufacturers and distributors eager for endorsements). THAT is the hallmark of successful keeping.
Someone dropped me the note when this subject came up before, as it regularly does in the newsgroups and mailing lists:
"Yes, it is possible for the ig to live for a few years on a dry food diet. My friend had hers on the pretty pet foods for juvi igs. If you read the container it says not to add any suppliments and to feed it only the dry ig food. For 6 months, her ig ate better than she ever saw it eat before. It even grew at a fantastic rate. I was tempted to try her method myself. Then, one day, I looked at the ig and realized that he could bend his lower jaw in 5 spots. After a good scream from my friend, we went to the vet and found out that it was MBD. It took a while, but the ig is doing better. It only eats real food. No dry stuff." email@example.com
I just got a copy of the 1995 ARAV conference proceedings which contains three papers by Susan Donoghue. One is titled "Evaluating Commercial Diets", presented with David Dzanis DVM. It discusses how reptile vets can evaluate diets and urges them to report problems associated with these diets to the manufacturer (which we all know isn't happening, unfortunately). They reference Susan's prior research (done at her nutrition research facility in Virginia - some of you may have read her article on what happened during the winter of 94-95 there), the study I referred to on r.p.h. (Donoghue, S. 1994. Growth of juvenile green iguanas (Iguana iguana) fed four diets. J. Nutr.124:2626S-2629S):
From Donoghue, S., and Dzanis, DA. Evaluating Commercial Diets. 1995. Proc ARAV, pp 74-79.
"Regulations for Commercial Diets
The parts of a pet food label of most value to veterinarians in reptile and amphibian practice may be the guaranteed analysis, list of ingredients, and the address for the manufacturer. Next in usefulness (but not on the label) is the phone number for the state Department of Agriculture, where complaints and questions about pet food are recorded. Also useful is the realization that due to resource limitations, regulating foods for non-domestic pets is a lower priority than foods for livestock, dogs, and cats. Many state departments may have neither the time nor manpower to routinely investigate commercial diets marketed for reptiles and amphibians. Because of this, don't assume that what is on the label of a product is reliable, that the diet inside is sound, that quality control was in place during manufacture, or that commercial diets provide a safe and effective alternative for captive reptiles.
"Feeding Trials: The best assurance of completeness and balance of a diet is a long term feeding trial throughout the reproductive cycle, then raising the young on the same diet. Such a trial could establish a diet for all stages of the life cycle as for the best of the products marketed for dogs and cats). The major manufacturers of dog and cat food maintain (or contract with laboratories that maintain) extensive colonies of these animals for feeding trials. In addition, their diets are fed to millions of dogs and cats. And, lastly, regulatory agencies are ready to field complaints about their products.
"Contrast the situation with reptiles and amphibians. How many manufacturers maintain colonies of animals, publish results in reviewed journals, and fund extramural testing? How many times have you contacted a manufacturer for verification of nutrient content? How many complaints have reptile owners lodged with regulatory agencies?
"Iguana Feeding Trial: Uncertainties concerning commercial reptile diets prompted a feeding trial in juvenile green iguanas. Three commercial diets marketed for young iguanas were compared: a canned diet [Tetra], a gel, and a dry meal [Zeiglers]. A fourth diet was made from fresh romaine, dry clover and dandelion, soybean meal, dry egg, vitamins and minerals. Iguanas were fed each diet for 6 weeks, then were accommodated for 2 weeks before another 6 week stint on another diet, and so on. Growth rates correlated with the content of protein and fiber. Iguanas fed the canned product (13% protein) lost weight, and those fed the gel diet (14% protein) grew slightly, just 6% over 6 weeks. Iguanas fed the dry meal (22% protein) averaged 31% increase in body weight, while those fed the romaine-based diet (31% protein) increased their weight by 60%.
"Similarly heeding evolution, when feeding commercial diets to herbivorous reptiles, we select products based on dried herbage (alfalfa and clover hays, for example, not meals and grain by-products). We try to supply long-stem fiber for hind-gut fermenters. For example, alfalfa cubes provide longer fiber than pellets and can be crumbled and mixed into fresh produce. In our experience, clover and dandelion are as nutritious as alfalfa, and more palatable, but not as widely marketed."
The opinions expressed in here (other than Donoghue's findings and conclusions) are my own, based on my observation of iguanas, conversations with reptile veterinarians and iguana owners whose iguanas suffered serious illness, even death, as a result of these diets, as well as research into the veterinary and biological literature.