My mother-in-laws dog bit her boyfriend on he neck.?

She calls my wife and says the human officer said the dog has to be put down and its head cut off for testing, that sounds a little barbaric to me. Do they do that and if so why would they do that? She has had the dog since it was born and its now 7 years old. They dont have a lot of money so i know it has ever been to the vet for any shots, but the dog isnt exposed to any thing to catch things like rabies.