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.
For a large part of the year cows on pasture will not eat any hay. The cows will be eating fresh grass and will need no supplemented hay. If the cow in question does not have access to fresh grasses or it is winter in your region and fresh grasses are not available the cow will generally consume twenty five to thirty pounds of hay a day.