The need to balance calcium to phosphorus ratios is quite widely known and acknowledged and there are many lists of foods with the ratios available. However providing foods simply based off this ratio is inadequate to assess a foods suitability for inclusion in the diet and opens the risk of not providing a balanced diet.
The quantity of calcium is also of great importance, too high or too low has the potential to cause nutrition related diseases either way. There are also factors that can inhibit calcium absorption such as fat, vitamin D, oxalates and other nutrients or antinutrients.
Insects do not generally have reasonable levels of calcium and their calcium to phosphorus ratio is typically negative. For the young bearded dragon, which require primarily insects, this places them at higher risk of not being provided sufficient calcium or perhaps to exceed levels as dusting with calcium can just as easily be overdone as underdone. However, to support the animal during this growing phase dusting and gut-loading insects is necessary. For the older bearded dragon that is consuming vegetation, supplementation may be reduced where it provides sufficient levels, bearing in mind inhibitors of calcium absorption.
Calculating the nutrient quantity and ratios
The nutrient values for food items are provide under Foods with the nutrient values for the stated weight. Select the desired items for the meal and the nutrients to be assessed into a table. The example below is based on an adult with a diet of roughly 50% leaf, 20% vegetable, 20% fruit and 10% insects. The total weight of the diet should generally be around 10% of a bearded dragon with an average body score.
Note that this is a very basic table and does not include all nutrients or antinutrients to be considered.
|Food Item||Serving||Weight||Ca (mg)||P (mg)||Protein (g)||Linoleic
|Blackberry raw||1/8 cup||18.81||6.35||3.57||0.21||1.17|
|Capsicum green||1/8 cup||18.62||2.18||4.41||0.16||0.32|
|Endive raw||1/4 cup||12.50||6.00||5.94||0.16||0.33|
|Kale leaves raw||1/4 cup||16.75||29.73||12.90||0.59||0.44|
|Turnip greens raw||1/4 cup||13.75||19.80||5.98||0.21||0.58|
|All Items||1 cup +
|88.69 g||65.31 mg||52.77 mg||2.23 g||0.04 mg|
The meal above totals one cup of vegetation plus 14 feeder insects (mealworm adults data based on fasted) and comes to a total of 88.70 grams. For a bearded dragon that weighs 500 grams this would equate 17.7% of its body weight which is excessive. However 10% is a generalisation, fruits and vegetables weigh more than greens due to the bulk for the same space, preparation (i.e. chop, puree, sliced) also makes a difference in weight per serving and there will be periods in life where more food is required than other times.
The calcium to phosphorus ratio of the above meal slightly exceeds one to one which on the surface appears to be adequate. However the total calcium should be around 1.5% of an ideal meal, this diet is only 0.74% and phosphorus around 0.75%, this diet being 0.59%, so even though the calcium ratio may be adequate, the total calcium is not. In addition this diet has also included 29.37 grams of oxalates, 16.87 mg of glucosinolates and 0.53 grams of fat; two of which have the ability to inhibit calcium absorption. Discussions on oxalates are rife and many foods are excluded because of it, however it is not as simple as whether a food has oxalates and trying to elimate foods with any such antinutrient is not only impossible but ignores the beneficial nutrients that are also available. Each plant will typically have insoluble and soluble oxalates. In addition, the tolerance levels of oxalates in the bearded dragons diet are not known, therefore we use ‘guesstimates’ based on human diets.
Dusting with calcium powder a few times a week will bring the calcium levels up, but even dusting has its issues. The calcium particles do not easily adhere to most insects and if the insect is not eaten immediately the calcium can be groomed off, or simply fall off, the insects body as time passes. To combat this feeder insects should be gutloaded and dusted. Silkworms simply require their standard meal of mulberry leaves, but other insects should be fed specifically targeted nutrients. The combination of gutloading and dusting will improve their nutrient levels and means vegetation does not need to be dusted, this is important especially for those fussy eaters who will quickly tire of the unpleasant taste which will generally tolerate it on insects.