I found this article as I have heard from another frog loving ponder that too
much protein in the diet of tadpoles causes deformities - note the comment
regarding watching for backleg development. Taddies do get protein on their own
in the pond (this article is about raising in containers) they will slurp up
insect larvae, snail eggs, baby snails, fish eggs... they just hoover along and
sweep up everything in their path. When in doubt always follow mother nature's
set-up. Taddies will eat their dead siblings but that is a relatively rare
event compared to constant algae and rotting plant consumption. The rare
exception is with some tadpoles, when the water get crowded, some will turn
carnivorous in order to speed up their development and get out of the pond
before it dries up. This involves actual physical changes to allow them to
consume and digest large amounts of protein.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is the article:

Tadpoles have a long, coiled intestine which is designed for eating plant
matter but they love protein when they can get it. Plant material can be any
variety of lettuce or spinach which must be boiled or frozen before giving to
the tadpoles. (Freezing uses less energy because your refrigerator is always on
anyway.) Organically grown lettuce is better so you can be sure it hasn't been
sprayed with harmful chemicals before you buy it. Old leaves with algae on them
from creeks can also be used as a supplement but these leaves could be a source
of disease so avoid urban drains. Do not use celery leaves!
Whatever plants you decide to try, make sure that they are not toxic and always
wash the leaves thoroughly, then boil or freeze them. There's a saying: "if in
doubt, leave it out". Even better than risking chemicals on commercially grown
crops is to use a compressed algae fish product called Algae Disks which might
be sold by your local aquarium or pet shop. A combination of food types is
good.
Protein can be given to the tads once or twice a week and increased to several
times a week after back legs have formed. Protein is very easy to provide
because tadpoles will eat bottom feeder fish food tablets. Many types are
available at your pet shop but a good one is Tetra Pleco-Min 5 Star formula
which contains a high protein algae called Spirulina. Some people use other
forms of protein such as cooked egg yolk or a chicken bone tied on a string and
dangled in the water but these will foul the water immediately and should be
avoided.
Feeding tadpoles requires small amounts of food frequently. You should only
throw in a small amount of food which will be gone in about 8 hours. It is
better to have to throw in food a couple times a day than it is to only have to
put more food in every other day. Don't put a couple days worth of food in to
save time - this will instantly foul the water and you'll have to spend a lot
more time doing a partial or full water change. A tadpole's whole life is to
eat constantly so keep an eye on the tank and add more food as soon as the last
lot is gone.

Entire article is here
http://www.fdrproject.org/pages/POtads.htm

k30a