Ark Country Store

Hand Mix or Formula Feed?

David Salmon, Ph.D. and Mark Griffin, Ph.D.

Traditionally, zoos and hobbyists have fed their reptiles hand made mixes of various items such as greens, vegetables, crickets, and mealworms. The bad news is that it is impractical, if not impossible, to make a hand mixed diet that is nutritionally correct and balanced. The good news is that Mazuri® has a line of formula feed diets that embody the most recent advances in reptile nutrition, and that these diets will serve as the foundation for an excellent diet for most of your reptile pets.

Why it is Hard to Make a Balanced Hand Mixed Diet
People sometimes hand mix a reptile diet based on the assumption that there are “good” ingredients and “bad” ingredients, (i.e. collard greens or grasshoppers are good, lettuce, kale or mealworms are bad, etc.), and that you can make a balanced diet by mixing up several “good” ingredients. However, no nutritional research has ever indicated that an animal needs a particular ingredient. Instead what an animal needs, and what we should be concerned to provide it with, is a balanced range of necessary nutrients. To see a list of these important nutrients, look at any Mazuri® specification sheet. These lists of important nutrient specifications include: amino acids (lysine, methionine, tryptophan, etc.); fat (often including levels of certain important fatty acids); fiber (usually by several different measures); minerals (calcium, phosphorus, iron, selenium, etc.); and vitamins (E, A, D3, niacin, thiamin, etc.).

Someone who wants to hand mix a balanced diet for his reptile must first know how much of each nutrient is contained in each of the ingredients that he uses for his mix. Then he must have in mind a desired profile of the nutritional requirements for the animal. Then he must mix in the correct amount of each item so that the overall diet achieves this desired nutritional profile. This is very difficult and very few people have the information, specialized equipment or time to do this properly.

Determining the Desired Nutritional Profile for an Exotic Animal’s Diet.
There are very few exotic animals for which there are generally acknowledged lists of nutritional requirements. How then can we determine a proper nutritional profile for these animals? We do not understand a reptile’s nutritional needs to the same degree of precision as we understand the nutritional needs of a chicken or a pig. That said, there is much that the science of nutrition can tell us about the nutritional needs of iguanas and tortoises.

For example, extensive work done with other vertebrate species has shown that past some minimum amounts the ratio of calcium to phosphorus is more important than absolute amounts, and that this ratio should be between 1:1 and 2:1. So an iguana or tortoise owner should be careful to keep the ratio of calcium to phosphorus in his pet’s overall diet within this ratio.

Similarly, each reptile species has a GI tract adapted to eating a particular kind of diet. A tortoise has a large fermenting hind gut chamber below his main stomach so it is clearly adapted to eating a high fiber diet, much like a guinea pig. A red eared slider has a much simpler GI tract with no appreciable hind gut fermentation and clearly needs a much lower fiber diet and amino acid levels that more closely resemble other animals with a similar GI tract.

This kind of information, coupled with a nutritional knowledge of a wide variety of animal species, makes it possible for a trained comparative nutritionist to select good nutritional parameters for most reptile species. While it is certainly true that many of these nutritional parameters will not have been subjected to as much rigorous testing as for domesticated species, these parameters will still be based on a thoroughgoing understanding of general animal nutrition and a growing body of scientific research for specific exotic species. This approach naturally leads to much better results than would trial and error or haphazard guessing.

Finally, it is possible to test the suitability of these nutritional parameters. These tests would include growing and breeding trials, with accompanying blood work where appropriate.

An Example of a Hand Mixed Iguana Diet
Let’s analyze an example of a hand mixed iguana diet below. With the exception of the alfalfa and vitamin tablet, most of the food items in the formula contain large amounts of water (over 90% in the case of strawberries) and nutritionally speaking only dry matter is important. For this reason it is useful to break down the ingredient mix in the above hand mix both on an as fed basis and on a dry matter basis.

Percent of Diet
Food Item As Fed Dry Matter

Beans, Raw Green 21.98 6.85
Squash, Raw 21.98 8.69
Parsnips, Raw 21.98 14.48
Strawberries 11.09 3.11
Alfalfa Hay 21.98 63.56
Centrum Vit. Tablet 0.97 3.13

Notice that on a dry matter basis almost 64% of this diet is alfalfa. Nutrient levels in all of these food items will vary, but let’s take typical nutrient levels, calculate the amount of each nutrient in the overall diet, and compare these amounts to the estimated nutrient recommendations for an iguana. (The vertical axis is the percentage of the recommended level for the nutrient. Recommended nutrient levels are not necessarily minimum levels, but those levels that Mazuri® consider ample and safe ).

How does this diet stack up?
On the plus side, this diet has good levels (107% ) of acid detergent fiber, which is important since an iguana is a leaf eating animal. Several minerals and vitamins either meet or exceed requirements. Amino acids (and consequently protein) are marginal, although this may not represent a serious problem since the nutritional requirements profile used here is very conservative.On the minus side, vitamin A is excessive (370% of requirements) which is troubling since vitamin A is toxic in large doses. Of more concern is the fact that the calcium to phosphorus ratio is 3.31, well outside the safe range of 1.0 to 2.0. This, coupled with the fact that there is essentially no vitamin D3 in the diet, indicates that an animal fed this hand mix would be at considerable risk of developing metabolic bone disease, particularly if it did not have access to high levels of natural sunlight. (Please see “Metabolic Bone Disease and Reptiles”, an article at our web site, analyzed, practically speaking there is very little that the average reptile owner can do to fix the deficiencies in this hand mixed diet. He could add small amounts of individual vitamins and minerals, add a mix of grain or legume based ingredients, and mix in a wider range of high fiber ingredients. But doing this well enough to successfully balance the diet would take immense study and effort, and in the end would require specialized equipment for analysis and manufacturing. In short, the reptile owner would need to become a nutrition company and his “hand mix” would become a formula feed.Balancing a Diet the Mazuri® Way
We recommend that you use a Mazuri® formula diet as the foundation of your reptile’s diet, adding other food items as enrichment. As an example, consider the option of feeding your iguana a diet of 60% Mazuri® Iguana Diet and 40% various fruits and vegetables. Percent of Diet
Food Item As Fed Dry Matter

Mazuri® Iguana Diet 5E07 60.00 92.78
Lettuce, Romaine 20.00 1.75
Apple with Skin 10.00 2.74
Kale 10.00 2.66

Again, comparing the levels of nutrients in this overall diet with Mazuri® recommended nutrient levels for an iguana:

Iguana Fed 60% Mazuri, 40% Greens and Fruit
Ca/P = 1.98

Clearly, this Mazuri® based diet is far better than the hand mixed diet we analyzed before. All nutrients are very close to recommended levels, and the calcium-phosphorus-D3 triad is very robust – calcium to phosphorus ratio of just under 2.0, D3 level of 8.3 IU/gm.

Make MAZURI® the Foundation of your Exotic Animal’s Diet
All Mazuri® diets are carefully formulated with your exotic pet’s particular nutritional requirements in mind. Mazuri® reptile diets were developed for zoos, tested in zoos, and used successfully by zoos for years. What our example here shows for iguanas is also true for other reptile species. Please see our technical article, “Metabolic Bone Disease and Reptiles” for complete feeding recommendations for a wide variety of reptile species.

Nutrition is a very real concern, so when you are searching for a well balanced diet for your reptile please give Mazuri® a try.

For More technical information about Mazuri products, visit