I intend to supplement 90% or more of the cow's food supply with hay purchased elsewhere. I know that keeping a dairy cow on 1/2 an acre is iffy, but I am willing to put forth the necessary effort to make it work. For me, it's a lifestyle choice rather than an economic issue. I thought about goats, but I actually don't really care for goat milk/cheese/meat. It has a flavor that I just can't bring myself to enjoy. Are you telling me that keeping a cow on 1/2 an acre can't be done, or that it is difficult? Difficult I can handle.
Is the half acre pasture, or woods? If it is pasture, it will be difficult since the cow won't be able to find all of it's own feed, but at least if you rotate the pasture (cut it into quarters) and move the cow to fresh grass, it can graze. If it is woods, you will have a cow, that can't do natural things like graze or find it's own feed, and will be supplementing 100% of it's feed, which = REALLY difficult, frustrating, and expensive...