If the 'Roadkill' challenge isn't sounding like fun to you, a relatively easy solution is to circle Sunrise Threshing, west of Fall's End.
Cows and bulls roam here and if you circle the farm, more animals spawn as you go around.
The only downsides are the occasional animal running into the woods or getting a cow stuck under your vehicle
but there's a handy garage at this farm if you want to grab another ride.
I'd say you'll be done in around 30-45 minutes.
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