About Horses and History?

I am writing an American Civ paper over the horse in America between the years 1492-1865. Does anyone have an sources about how the horse was used, who brought the first horses, etc., that can be used in an MLA style paper? Basically what I need is a ton of information on horses in America that can be cited. If I didn't have to cite the stuff I'd just use what I already know, but it has to be cited so please no information from Wiki-sources or just out of your own head. Thanks!