Giant herds of wild boar, roaming the plains. The herds would go on for days. Then the White Man nearly wiped them all out.
You need to read some books.
Bangs/brucellosis wiped most of the bison. My family raised beef in Texas. The cows had to have a bangs vaccine by 6 months of age.
Wild pigs also carry brucellosis and kill trees by rubbing on them and spreading oak wilt.