So about cows: like chickens there again will be a bunch of different breeds to choose from. For whatever reason I haven’t had as much luck finding information on them, so I’m going to have to use information I learned almost entirely second-hand from farmers… Which isn’t a bad source, actually. It lacks detail but maybe I can add some more later.
Of course they need a lot of space. A lot a lot. Well they’re large creatures and they like to roam a bit sometimes, so that isn’t unexpected. The unexpected part is when hearing about how a cow jumped a fence. I’ve never been able to confirm that cows can actually jump and it is possible that those people just meant that the cow(s) in question just broke through the fence and wandered off, but it does make me wonder about those fences. I can believe that a cow can break through a fence like it’s made of wet notebook paper and a couple of toothpicks, but I question how high of a fence a cow could jump. Not that it matters much. If they really want to leave, they will. If you care for them properly then you shouldn’t have to worry about it.
Speaking of caring for cows, different breeds are said to produce different amounts of milk. Individuals within breeds and mixed-breed cows can dry up regardless of genetic background, so if you happen to be looking to buy a cow and you see something that looks like a bargain from something that’s supposed to be a really good breed, of course you shouldn’t trust the person trying to sell her to you. She might only be good for burgers. Maybe she was born with a twin brother and the person selling her tells you she hasn’t dried up… That’s because if a cow is born with a twin brother she won’t produce milk. Ever. Twin girls are fine, though. It’s just the cow + bull combination that you don’t want. So it’s just like ordering things off the internet. Do your research and don’t trust people.
Furthermore, if you want to care for a cow, be prepared to wake up around 4:30 in the morning to milk her and then go back to do it again later that afternoon. They need a lot of attention and if they don’t get milked when they need to be, it will cause them to be in physical pain. That isn’t a problem that weighs equally on all kinds of cows, though. The older kinds that haven’t been bred to produce copious amounts of milk (you can tell they haven’t been bred for it because their udders are so much smaller that it’s plainly obvious) supposedly don’t have that problem as much.
So it’s up to you to decide how much cow milk you think you’re going to drink in a given amount of time and then to pick a kind of cow that should produce an amount of milk close to that (if you’re just going to drink it yourself that is). But if you want to start a dairy farm or something then go ahead and get more cows. If you don’t really ever feel like drinking cow milk, then I’d recommend saving yourself the giant cash wad it takes to buy and care for one or more cows and just get something else that will help you be more autonomous.
Personally, if I had to choose between buying and caring for half a dozen chickens or one cow, I’d definitely go with the chickens. That’s just me though.