My Dad and I tried that back around 92 or so. Ran 70 head on 40 acres. Was not to long before they turned it all to dirt. Had to buy loads of hay to feed them after long. My neighbors seen all that hay and would buy some here and there. Sold the cows and lost money but seen that hay sales were keeping things going. So in 94 we opened a feed store.
But thats here in SoCal were we don't get much rain. Only have 3 horses out there now and still have to feed them a few months out of the year.
I know PA gets a lot of rain and every thing stays nice and green but I don't know if 12 is enough for even one cow. They can put down over 100lb of hay every 4 days or so.
