It may be that I am ignorant of animal welfare standards in the UK, but I think I'm right that British cows spend a lot of time out of doors grazing on grass, and that a lot of the silage fed to them during the winter is also based on grass. I also know that growth hormones are banned in the UK which is why you won't find American beef for sale there. And generally we don't enrich or fortify our milk with vitamins.
Faced with a cold cabinet of milk here, the decisions are a bit more complicated. What do I care about? Well, I don't want to drink milk from cows that have been given growth hormones. The US FDA (Food and Drug Administration) has decided that these are harmless to people but they are banned in the UK. Call it patriotism, or scepticism but I'm not keen on artificial means of increasing production which then cause increased levels of infertility and other problems in the cattle, as well as increased levels of an insulin like growth factor in the milk.
I would also prefer to drink milk from cows fed on grass out of doors. Now that one is tricky. I'm currently reading The Omnivore's Dilemma by Michael Pollan and have just got to the part on "big organic". Most cows in the US live in barns and not in fields. That's all the time, which to me just seems wrong. Does going organic guarantee that the cows are grass-fed? Not in the USA where more cows are corn-fed than grass-fed. Apparently when the US was designing its organic standards, to ensure that the industrial scale organic dairy farms could meet those new standards, they were made vague and weak. Currently cows must have "access to pasture" but there's nothing to say how often or whether they actually get to eat it. See what I mean about vague. I'm trying to find milk from grass-fed cows. Currently I'm buying Organic Clover Stornetta milk which is apparently from small farms in California and is I think from partially grass-fed cows. I just wish someone would tell me if I got this particular shopping test right.