by Kenneth L.
Vitamin A and it's effects are more complex and less understood than vitamin D. I am simplifying the subject for a few reasons. One is to avoid losing readers due to 3-block-long words, another is because there are a few great references that spell everything out, and third, because I don't want to work that hard right now. I know parts will be in direct disagreement with other veterinarians points of view. These are only my thoughts, do with them what you will.
The players: Carotenoids: Provitamins that occur with chlorophyll in all green plants Retinol: The form vitamin A takes in animal tissues. Usually changed from carotenoids to retinol by cells in the intestinal mucosa and/or the liver. Stored (as esters) in liver. Chylomicrons: Lets call them "escorts" for simplicity. They grab the newly formed retinol with one main mission in life, to get the retinol to the liver. Vitamin D3 (see previous post, someone should still have it) Vitamin E
So, here are some more complexities. How many times have you read posts on these lists that go something like this: "I alternate Calcium plus D3 on one day with Multi-Vitamin Powder every other day" The same people often later ask "What causes swelling under the chin of my cham?"
With vitamin A, which can potentially store in the liver for up to 6 months, and vitamin D, which can store for a couple months in the liver as well, we should be seeing big problems, right? If you remember from the vitamin D post, excessive D3 is associated with calcium mobilization from the bones as well. Working together (A & D) the cham should look like Gary Larsons rubber chicken ranch, right? Actually, vitamin A and vitamin D are antagonistic (incompletely)to each other. While both may be at toxic levels, the effects are not as evident due to their interaction. The funny thing is, once signs of MBD show up, people often start shoveling in the calcium and D3, in an ALREADY hypercalcemic cham! This is kind of like hating how tired Valium makes you so taking an amphetamine with it. Some species are EXTREMELY sensitive to vitamin A. Some (few) can take a boat-load without signs of problems.
My opinion (for what its worth) is preformed vitamin A is a medication used to treat severe cases of hypovitaminosis A and symptoms suggestive of such. It is too dangerous to use as a supplement. I use it carefully to elevate vitamin A levels. I sometimes use it to treat vitamin D toxicosis. I also use it when there is liver dysfunction. Bile salts are required for the uptake of retinol into the liver. I also use vitamin D to treat vitamin A toxicosis (along with vitamin E which seems to help).
Chams do not have much opportunity to zap preformed vitamin A in the wild. There is probably some small amount in most insects, especially king mealworms that pass through the liver while eating their way through another chams body (just kidding, I always liked that wives tail). There are so many successful breeders out there who properly gut-load their insects and DO NOT use preformed vitamin A, how can it be considered a good idea to take the risk? If supplementation is needed, the provitamins are a good choice. There is another consideration on which provitamins, but that is too long for this post.
Once again, these are my thoughts from my personal experiences. Your results may vary. (standard disclaimer). Discuss all concerns with your herp vet before making drastic changes to your husbandry. If anyone desires references for any of this info, I can send it upon request.
The information provided on this site is for your consideration only. You should contact your veterinarian for specific questions concerning your chameleons.