Help me with deciding in what tractor for a cow farm? please?

I have to do a project for ag cl and we have to include all the neccesities for a cow farm of 100 cows. I have no idea what kind of tractor and what all I need for the tractor, I have looked at every site possible for information and didn't find what I need. PLEASE help me? I know that I need a hay bale spear to be compatible with the tractor and the tractor needs to be 4WD. I don't think it matters what kind. as long as the hay bale spear is compatible with the tractor. I know NOTHING about cows and tractors. No, I don't want you to do my homework for me, but I do need to know what kind of tractor I need. Thank you so much!