Mini-cows are available in The U.S., but judging by the ads I've looked at, they are very expensive. So if you have thousands of spare dollars just lying around in the way, looking for something to be spent on, mini cows might be nice. They eat less, are easier to handle and transport, of course, because they're small. You can keep them on less pasture than full size cattle.
Some day I'd like a milk beast, maybe a cow, maybe a goat. More than likely, if I get a cow, it'll be a smaller breed, like a Jersey or a Dexter, (or a mix of smaller milk breeds) but regular size.