For juvenile dragons...roughly 6-12 months old, feed insects once a day, greens offered all day as well.
Instead of crickets or in addition to them, silkworms, butterworms, various species of roachs (especially the young of larger roaches) small horn worms (not wild caught, these are toxic. They can be bought to be used as reptile feeders. These are raised on a special chow that lacks the toxins the wild ones normally accuminate from the foods they eat in the wild), some superworms, waxworms and the new phoenix worms, these last three should not be everyday but can be offered once a week as a treat.
I suggest dusting with calcium without phosphorus but with vitamin d3 once every other day. A multivitamin once a week for juveniles, once a month or once every other week with adults.
Canned vegetables are useless. Most of the nutrients have long since leached away during processing. Frozen vegetables are better but lack a couple nutrients which are destroyed in the process of freezing (thalimine is one, I beleive). This shouldn't be too much a concern as dusting with multivitamin on the insects will balance it. However, you need to feed a much greater variety of greens than what can be found frozen. The website below has a great charge for what greens are good for dragons and how frequent they can be used.
www.beautifuldragons.com
The real important thing is to give your dragon as much variety as possible. This is the best way to ensure he is getting a healthy diet. Even bad greens, such as spinach, romanine, kale etc are not as bad when mixed with several good greens, such as collard greens, dandelion greens, etc. I find what works best is to use two or three big staple greens (ie collards, dandelion greens) then add different greens and vegetables, such as kale, parsley, zuccini, bell peppers, endive, escaroli etc, rotating between them every couple weeks. For additional variety, I often chop up seedless grapes (one or two grapes, depending on age of dragon), a few blue berries, strawberries etc and sprinkle it ontop of the greens. Various edible flowers are great for treats as well, such as dandelion flowers (make sure they have never been in contact with any herbicides or insecticides), hispiscus flowers, panseys etc.
Another thing to consider is insects should be reduced as the dragons age...adult dragons (14 months ) should only have 10% of their daily diet insects, the rest greens and vegetables. Hatchlings and very young dragons are the opposite, needing about 90% insects and only 10% greens/vegetables. Juveniles and young adults fall in the middle of those extremes...roughly 40-60% greens.
There will always be some variation on how people raise their dragons. Some people like to offer a few insects every day to their dragon as well as their salad. Others feed insects a couple times a week. There is no set in stone method so finding what works for your dragon may take a bit of experimentation.
One other thing to remember is the food you give your dragons is only as good as the food given to their food...that is to say, what you feed your insects will reflect on how good they are for your dragon. Typically, store bought crickets are not well fed, some may not be fed at all, thus, feeding these to your dragon right away, is feeding them next to nothing but empty shells. Its like feeding a chicken egg after the contents have been sucked out of the shell, leaving just the shell itself.
Thus it is very important to gut load insects. For crickets, roaches and other insects that eat a variety of foods, feeding them at least 24 hours before giving them to your dragon, isthe best way to ensure they are full of nutrition. For crickets, feed them the exact same greens and vegetables you feed your dragon, add crushed low fat dogfood, fish flakes, store bought gutload, chicken mash or similar stuff to your crickets. I beleive you can feed much the same to most species of roaches as well. It also helps to add some plain calcium powder and multivitamin to the insect food as well (very small amounts, a pinch of each is more than enough, depending on the size of batch of food prepared).
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PHLdyPayne