I recieved a posting on facebook that someone forewarded about pet food contents with regard to the melamine poising a few yars ago due to imported ingredients. They pointed out that many of these added vitamins are because cooking the food, and heating it in the canning process causes it to lose vitamins which then have to be added back in. The point of the article was that these added vitamins often come as a pre-mix that the pet food manaufacturers buy from other sources, and the labels don't state if the source is over seas or not. I can't speak as to the acuracy of the statement about the source of the pre-mix, but it does make sense to me that vitamins would be lost in cooking and need to be replaced.
If I can find the link to that article again, I'll post it here.
