Slaughter traditionally means to kill lots of things at once- you don't really slaughter one chicken, you just kill it. You slaughter 20 of them.
There has been talk of removing that from the ordinance because so many people are thinking along your lines- they misinterpret the intent of that part of the ordinance (to prevent people from killing a whole bunch of chickens in their backyard i.e. disturbing the peace) and think that it means you can't even kill one. I suspect it won't be in the final draft, which is fine with me. Misinterpretation is not desirable!
Montana IS vast and rural, but Missoula itself is a city of about 70,000 people mostly living on 45x100 ft lots. It is tucked up under a series of mountains and rivers, surrounded on all sides by publicly owned lands, so it is pretty compact.
-MTchick