Do you have a citation for the horse number? My research [0] shows we have a 1/5 out peak number in ~1900 and our population has 5x since then. This means per capita horses in the country is down 96%, while absolute count is down 80%. Both are huge numbers.

0 - https://datapaddock.com/usda-horse-total-1850-2012/

The page you linked doesn't count recreational horses.