biggest buffalo round-up of its kind for the past 45 years. so what's the best part of the round-up, bob? >> well, to me, it's the run. when you're actually pushing the buffalo and they're running just s hard as they can run, we're unnning as hard as we can run, it's an adrenaline-kicking son of a gun, i'll tell you that for a fact. >> reporter: a lot of fun, yes, but a buffalo can weigh 2,000 pounds, and some of them have an attitude. just ask first-timer chris richgels: >> well, i had a bull turn and .ome at me on my horse, and we had to boogie out of there pretty quick. it made for a memorable event. >> reporter: more than 30 million buffalo once roamed the u.s., but in the 1800s, they ofre slaughtered by pioneers lamost to distinction. today one of the country's largest wild herds calls custer state park home. there is a purpose to this round-up. >> yes, very definitely. >> reporter: it's for the health of the herd. >> the health of the herd, to hold the herd in a manageable