Reptile Dietary
Supplements
Essential additives, or unnecessary
performance enhancement?
Dr Thomas Vowell, of Glenorie Vet Clinic, explains why the diet
of many captive reptiles is lacking in vitamins and minerals
One question I often hear around the topic of reptile
supplements is: “Should I use calcium and vitamin
supplements for my reptiles? Wild reptiles don’t get
supplements and I feed mine the best food I can buy!”
Not all orders or suborders of reptiles require dietary
supplementation in captivity. For example, snakes and
monitor lizards, which consume whole vertebrate prey
such as rodents, rabbits, quail, etc., will obtain an
appropriate balance of calcium and phosphorus (Ca:P)
without the need for supplements. The skeletons of
their prey items will contain sufficient calcium, and the
livers will also be rich in other micronutrients such as
vitamin A. However, dietary supplements are essential
for omnivorous or insectivorous lizards and turtles. The
simple reasons for this are that commercially-available
invertebrates don’t always contain the nutrients
required by your reptiles, and the variety of food items
available to free-living reptiles is far greater than that
of those in captivity.
Food nutrient content.
Most commercially-available invertebrates have a Ca:P
ratio that is too low to sustain the majority of reptiles (see
table). The ideal ratio for most reptiles is 2:1, which
means that the diet will contain twice as much calcium as
it does phosphorus. If the ratio is too low, then the reptile
will resorb calcium from its bones, leading to fractures
and a wide variety of other medical problems.
Most studies have found that feeding crickets a high
calcium diet (>8% Ca) is unpalatable for the insects,
which retain much of the extra calcium in their intestinal
tracts. For this reason, it is important to feed out crickets
on a high calcium diet within a matter of hours, otherwise
the additional calcium will pass through their gut and not
be delivered to the reptiles.
Species
house cricket Calcium
(mg/100g)
40.7 Phosphorus
(mg/100g)
295 Ca:P ratio
(ideally 2:1)
1:7.3
mealworm larvae 16.9 285 1:16.8
superworm larvae 17.7 237 1:13.4
waxworm 24.3 195 1:8
Mineral composition of common, commercially-available invertebrates.
Adapted from Doneley et al (ed.s), 2018.
The advantages of a free-living diet.
Obviously, free-living wild reptiles do not receive
calcium or vitamin supplements as part of their natural
diet. So, it would make sense that if we can provide their
captive counterparts with conditions that are as close as
possible to those of their natural environment, we would
not need to give them supplements either. However, as
hard as some reptile keepers may try, it is impossible to
Knowledge of the biology and captive
care of invertebrate prey items is essential
‘When choosing a
for successful management of this food
supplement, consider
source. Gut loading of the prey items is a
what may be missing
practice used to correct the nutritional
in your pet’s diet.’
content of invertebrates, by providing
them with a high nutrient diet prior to
being fed out. In one study Fox Geckos
(Hemidactylus garnotii) and Cuban Tree
Frogs (Osteopilus septentrionalis) were fed
crickets that had been gut loaded with a
high calcium (8% dry matter) diet which
increased the calcium content of the
crickets from 0.2% to 1.3%. The Fox
Geckos demonstrated a significant increase
in body calcium, whereas the Cuban Tree
Frogs showed no marked improvement.
Image by bluedog studio.