Information for travelers at the Centers for Disease Control and Prevention (CDC) website. There are other links there.

Restricted Products at the US Dep't of Agriculture Animal and Plant Inspection Service (USDA/APHIS).
Their main Foot and Mouth page - more links.

I'd predict that customs will ask if you're bringing any prohibited items, and may check your luggage for them. They'll probably also check your shoes and property for dirt. They'll probably ask if you've been to a farm, zoo, or other animal facilities in the 5 days before leaving.