Rats are common at stables? Don't worry about them?

Wasn't the black plague caused from rats? something to do witht he feaces or something like that. Rats carry a lot of diseases, so Im in agreeance with you. I love animals, but i know that rats are probably the worst rodent to have in a stable. Especially when they are in the horses feed. Yes rats are common pretty much every where you go, but they still need to be eradicated, especially around areas of food. Health regs, dont think its Okay for the rodents to be around in resturants and food, so why is it different for animals?