Livestock needs protein to be productive, just like we do, and one very economical way to supply that protein to them is to feed them other animals. It sounds a little bit sick, but, literally, in other countries old cows and old ewes were ground up and fed back to their children, because then that would increase the protein content in their feed. But in the United States, it's a law, you cannot feed animal products to food animals. So you don't have to worry about that line of transmission of the disease.
The main reassuring fact, however, is the fact that we've not identified any cases of Mad Cow in this country.
In fact, ironically, if Mad Cow disease were to occur anyplace in the United States, where do you suppose it might occur?
"Clayton is a land range scientist, but he knew sooooo much about virology. He told us that Mad Cow Disease could get into this country from cows coming across the Mexican border... and then the very next day the newspaper had an article about cows being found with MCD in Texas that had come across from Mexico."