Whether putting food in the refrigerator, the freezer, or the cupboard, you have plenty of opportunities to prevent foodborne illnesses. One of the basics of food safety is cooking food to its proper temperature.
I personaly always figured around 25lbs of hay per day for a average size cow when i was putting up hay. Alot of that of course they can get if pasture is available/accessable. Multiply that by your number of cows x average days you actually have to feed.
So if she is thin, she may need to add weight as the fetus develops - about 100# of gain before she calves. So, a 1200# cow needs roughly 24# per day of hay to maintain her weight, plus another 750# of feed over the next 3 months to compensate for the fetal growth - an additional 8# of hay per day.