by rpavlis on Sat Dec 16, 2006 6:39 am
Unfortunately protein is more complex than a single thing, there are 20 amino acids that make it up, and what becomes deficient is certain ones of these amino acids. Animals can make ten or so of them from other dietary items, but have to eat another ten or so.
There frequently developes serious problems with birds being deficient in TWO of the amino acids, methionine and lysine from eating only vegetable protein Lysine deficiency is very common, and methionine deficiency can lead to very serious complications very quickly, especially liver disease.
Methionine is involved in making choline, and is involved in several important biochemical reactions in addition to being used for proteins. Lack of it, lack of B12, and lack of folic acid can lead to rapid accumulation of fat in the liver. Geese and ducks are deliberately fed diets to cause this to occur for the production of foie gras. (A food whose production I consider causes severe cruelty to animals.)
In spite of what your vet said, I have serious doubts about feeding much tofu long term, because soy beans contain a toxic terpene and is very deficient in methionine and not very rich in lysine either.
Animal protein has about 7% each of lysine and methionine, but plant protein is usually less than 2% in these. There have been cases of tryptophan deficiency. However, animal protein typically has about 1% tryptophan, so animals do not need much to avoid deficiency.
Soybeans, like other beans, is seriously deficient in methionine. Maize is very seriously deficient in lysine.
Again, the problem with methionine and lysine derives from the fact that plant protein has much less of these amino acids than animal tissue, so animals have to eat a lot of vegetable protein to get enough. But eating too much protein can contribute to gout.
It is interesting that the protein in both the egg white and yolk have very similar composition (but dramatically different compositions for other nutrients.) As you might guess, the amino acid analysis of both is near perfect for animals, since it serves to nourish the developing embryo.
Milk products have similar amino acid distributions for similar reasons. Milk products, however, containing lactose or galactose are not good except in low quantities.
Will puddles eat hard boiled eggs? I never fail to feed all of the members of my flock a small slice of egg each day, trying to get them some hard boiled yolk and hard boiled white in the slice. I try to get about 1/20th of an egg or so per large bird per day. I also put the shell fragments in their food as well.
Although parrots are primarily vegetarians in the wild most, if not all, of them eat some animal protein. A few are down right preditors. I saw a video once of a wild cockatoo cleverly breaking snail shells by "bombing" them with rocks to get at the flesh inside.