"I wonder how many horses/oxen it would take to pull a bus. Maybe you could park the buses in a circle and keep the livestock in the middle, like a mobile corral/colony?"

"I checked into that. Apparently a full grown draft horse can pull about a ton without straining itself, provided it has a good weight distribution harness. An average full size school bus weighs about 10 tons, so 10 horses per bus. That's only the bus and driver though; no supplies or passengers. So it would probably be more like 15-20 horses. I think you'd have to consider speed, too. You don't want to be moving at a crawl if you're moving through hostile territory. Another thought is whether or not the horses would attract zombies. Would they try to eat them or ignore them and go for you? Parking the buses in a circle to corral your horses might work at night, but only if you block the area between the wheels so nothing can get under them."