From: donb@igor.tamri.com (Don Baldwin)
Subject: Iguana Care Sheet
Organization: TOSHIBA America MRI, South San Francisco, CA
Date: Sat, 5 Sep 92 00:23:33 GMT

     Green Iguanas: Their care and Captive Husbandry
     By Norman Frank, DVM
     From Reptile and Amphibian Magazine (Jan/Feb 1992)

Feeds, Feeding, and Environment

     Among reptiles and amphibians, a carnivorous diet is the rule.
Virtually all frogs and toads, as well as salamanders, snakes, and
crocodilians eat other animals to meet their own energy
requirements. Among turtles and lizards the trend continues, but
some species also add vegetable matter as a food source; and a very
few forsake all meat and exist exclusively as vegetarians. The
green iguana is a member to the latter group, and from a management
point of view, this imposes very strict conditions upon their
owners. There is no mixture of fruits and vegetables which, in and
of itself, will provide a completely balanced diet to a herbivorous
animal. The reason for this is because there is no vegetable source
of vitamin D3, the biologically active form of vitamin D. Vitamin
D3 is a fatty substance needed for calcium digestion; and without
calcium to facilitate muscle function and bone formation, any
animal will die.
     In the wild state, green iguanas produce their own D3 when
they bask in the sun. Ultraviolet radiation, striking the skin,
activates a cholesterol-like substance, converting it to the active
D. This then enters the bloodstream and is either transported to
the liver and fatty organs for storage, or used immediately to
initiate the absorption of dietary calcium.
     The herpetologist who feeds a completely vegetarian diet to
an iguana, therefore, must insure against vitamin D deficiency by
exposing the reptile to sunlight. Such exposure should be direct,
not filtered through window or cage glass. In actual fact, many
zoos and private hobbyists move their iguanas into outdoor pens
during warm weather so that they are able to bask. These periods
need not be extensive to yield results; a few hours a day for three
to four months will provide an iguana with the opportunity to form,
and store within its fatty tissues, a good dose of D3. A convenient
way for moving adults is to house them in wire cages which have
wheels attached to them. In this way, the entire cage can be rolled
around, from inside to outside, as temperature and weather
conditions dictate.
     A second way to provide the ultraviolet radiation of sunlight
is by the use of full spectrum indoor lights such as Vita-Lite
tubes. These fit into standard fixtures and provide the entire
range of wave lengths found in sunlight. Like natural light, these
rays must not be filtered through glass. Indoor lighting is
generally not as "strong" as natural sunlight, and should be
utilized during the entire year.
     A third method of providing vitamin D3 to an iguana is by
supplementing the diet with a commercial additive. Pharmaceutical
companies produce D3 by exposing animal fat to ultraviolet
radiation. This sets up a similar biochemical reaction that natural
exposure sets up in a living lizard, and the resultant D3 is then
prepared in powder or tablet form, ready to fortify the herbivorous
diet and make it complete with respect to D content.
     Once the iguana owner provides a source of D3, the animal can
absorb calcium from its diet and the challenge then becomes
providing fruits and vegetables that are rich in this mineral.
Table II lists common feed used and the calcium content in a cup
of each. In order to qualify as a "good source of calcium" an item
must meet two conditions: 1) it must actually contain a high level
of calcium compared to other feeds, and 2) the calcium level must
be equal to, or higher than, the phosphorus level; in other words,
the calcium to phosphorus ratio must be at least one-to-one or one-
to-less than one. Under natural conditions it is not possible to
supply too much calcium in the diet; any excess is passed through
the intestines and eliminated in the feces. It is interesting to
note, however, that dieticians working under experimental
guidelines can induce excess calcium retention with massive doses
of ultraviolet exposure or by the administration of toxic levels
of irradiated fats into the diet. This illustrates the close
relationship between vitamin D3 and calcium.
     To this point, the discussion has involved a vegetarian ration
only. This is the natural diet of iguanas which are physiologically
equipped to handle the high fiber/low fat content of a no-meat
diet. They have a modified intestinal tract containing a large
colony of symbiotic bacteria. It is the function of these
microorganisms to break down the high cellulose diet into secondary
products which the lizard then absorbs. The process is called hind-
gut fermentation and it supplies approximately half the energy
needs of the iguana - an impressive figure. Yet there are many
captive specimens, especially juveniles, which eagerly eat meat in
the form of pinkie rodents, worms and grubs, crickets, and canned
dog or cat food. Expert opinion is divided on whether it is
advisable to feed these items, but common sense suggests that,
since their taste for meat is natural, a small portion of the total
diet (5-15%) can be animal-based and fed to those individual
lizards who desire it. Table II compares the Ca:Phos data of
several meats. Notice that only pinkie rodents and worms meet the
1:1 calcium to phosphorus criteria. It is a misconception  that
insects have a calcium shell and are therefore good sources of the
mineral. The exoskeleton is actually chitin, a complex sugar, and
insects should be dusted with calcium powder or raised on a
calcium-rich substrate prior to feeding. Table II lists a normal
cricket, and compares it to one raised on a feed fortified with
calcium-rich limestone. The experimentally raised insect meets the
ratio standard. A word of caution is advised for people who use
commercial dog and cat foods; many are already fortified with
vitamin D3 (labeled as D-activated animal sterol) and if given in
excess may induce calcium overdose, in the same manner as seen in
laboratory experiments.


Table II: Calcium and Phosphorus Content of Common Iguana Feeds

               1 Cup Portion     Calcium   Phosphorus  Ca:Ph Ratio
  Good         Collards          218 mg     29 mg         1:0.1
 Calcium       Rhubarb           105 mg     17 mg         1:0.1
 Sources       Turnip greens     105 mg     23 mg         1:0.2
     *         Chinese Cabbage    74 mg     26 mg         1:0.3
     *         Dandelion greens  103 mg     36 mg         1:0.3
 Mix As        Parsley           122 mg     38 mg         1:0.3
 Basic         Kale               90 mg     38 mg         1:0.4
  Feed         Cabbage            32 mg     16 mg         1:0.5
 Ration        Leeks              73 mg     43 mg         1:0.5
     *         Green Onions       60 mg     32 mg         1:0.5
     *         Spinach            51 mg     28 mg         1:0.5
     *         Blackberries       46 mg     30 mg         1:0.6
     *         Yellow Wax Beans   63 mg     46 mg         1:0.7
     *         Okra               82 mg     64 mg         1:0.7
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 Marginal      Celery             44 mg     32 mg         1:0.7
 Calcium       Eggplant           30 mg     26 mg         1:0.8
 Sources       Squash             36 mg     26 mg         1:0.8
     *         Radish              9 mg      8 mg         1:0.8
   Use         Green Beans        41 mg     42 mg         1:1
 Sparingly     Pears              19 mg     18 mg         1:0.9
   For         Apples             10 mg     10 mg         1:1
  Variety      Sweet Potato       29 mg     37 mg         1:1.2
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   Poor        Cucumber           14 mg     18 mg         1:1.2
  Calcium      Strawberries       21 mg     28 mg         1:1.3
  Sources      Broccoli           42 mg     58 mg         1:1.3
     *         Lettuce            20 mg     26 mg         1:1.3
     *         Parsnips           70 mg     96 mg         1:1.3
    Use        Apricots           15 mg     21 mg         1:1.4
   Rarely      Brussel Sprouts    36 mg     60 mg         1:1.6
     *         Cauliflower        28 mg     46 mg         1:1.6
     *         Peaches             5 mg     11 mg         1:2.2
     *         Asparagus          28 mg     70 mg         1:2.5
     *         Beets              22 mg     66 mg         1:3
     *         Bananas             7 mg     22 mg         1:3.1
     *         Plums               2 mg      7 mg         1:3.5
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   Meat        Pinkie Mice        1.6 %     1.8 %         1:1.1
     *         Earthworms          .95 %     .95 %        1:1
   5-15%       Crickets            .16 %     .87 %        1:5.4
    of         Crickets (lab)      .77 %     .88 %        1:1.1
   Diet        Mealworms           .038 %    .57 %        1:15
     *         Canned Pet Food     .3 %      .2 %         1:0.6