While adding no nutritional content, the additives high nitrogen levels makes a food look like it's chock full of protein. And it's certainly cheaper than actual food.

In China, they make melamine from boiled coal. Mmm, yummy coal! Makes kitty's fur lustrous and eyes so shiny! — BEN POPKEN

Filler in Animal Feed Is Open Secret in China [NYT]
(Photo: Ariana Lindquist)