I remember this happening, and the pet food scandal just before it. Melamine was being added to pet food and milk powder to falsely increase their protein values. Enough to cause kidney failure and sometimes death. I used to do protein analysis for food products, and could see how easy it would be for food companies to cheat like this. The percent nitrogen content in a sample is used to estimate the protein value. Melamine powder contains a lot of nitrogen, so it’s blended in to bump up the final protein values. Really shitty thing to do, knowing that it’s toxic.