I can pack 8-10 cows in fairly tight in our alley - it's a wider than ideal alley for cows in single file but loads up well for vaccinating. Oh, you still get the odd cow that gets snorty and thrashes her head about or tries to burrow under the one in front but on the whole with a walkway so you are above them I find there is less upset that catching them in a chute. If I'm giving 2 shots I do one walking one direction and the other on the way back. The tighter you can pack them in the better it works though.