I just discovered Erin Davis and her site while looking for unrelated content. She's done some great work with maps and statistics including this map showing what counties have more livestock than people (data is from the USDA).
I love the big circle legend. It lets you dig into a complicated multi-variate color scheme so you can see that, for example the green areas (such as southwestern Wisconsin and northwestern Arkansas) primarily have a combination of cows (blue) and chickens (yellow) and not so many pigs. Black areas such as in Montana have more of all three than people.
Scroll down the page and you can see the individual maps for each animal plus maps of counties with more goats, sheep and turkeys than people.
Finally, at the bottom is a map of the most common type of livestock by county.
For the entire map set go
here.