Another variable, of course, is quality of the hay. A bale of hay is only as good as the meadow from which it's cut. If you're uncertain of how to judge quality, before purchasing hundreds of bales of hay, buy one and take it to an experienced farmer for an assessment.
When buying hay for the first time from a farmer, also pay attention to the weight in relation to the size of the bale. You can't pick up a round bale, but you can pick up a square bale. If it feels lighter than it should, the farmer may be "baling light" and selling underweight bales - which is only fair if the price is also underweight. (Another clue is loose strings.) Most people won't try to cheat you, but there are always a few bad apples. The price of the bale should be fair in relation to both the weight of the bale and the going rate for an average bale in your area. Find a hay man you can trust and be his favorite customer.
Last winter, with the round bales I had then, I found that my two cows would go through a round bale about every five days, so the round bale was worth about 10 square bales (after accounting for the excess waste because the round bales weren't covered-without so much waste, each round bale would have been worth more).
If I were buying the same size round bales for this winter for the cows and not covering them, I would plan on at least 18 round bales to get me through the worst of winter, considering that I leave them on pasture into December and have them back on it at least partially by late March, unless it's an extremely harsh winter. You never know what your winter is going to be. And I would have some extra square bales stashed in case I ran out. And that's just for the cows, not counting the round bales I'd need for my other animals.
This winter, I went with square bales for everyone. Planning 100 bales per large animal, that meant 200 square bales for my two cows. I have two horses - 200 square bales for the two horses. That's 400 square bales for just four animals. I packed in another 300 square bales for the rest of my animals.
While the hay-for-winter equation has many variables, you can always start with the rule of thumb (100 square bales per winter per large animal or 100 square bales per winter per upwards of half-dozen smaller animals) to at least get a finger hold on what you need to provide when planning to bring animals on to a farm.
In deciding how many and what size animals you can afford to keep, take the rule-of-thumb number of bales and calculate it based on the cost of hay in your area. Hay price is another variable, and it varies widely. I buy square bales for $2.50 bale. When I look at a cow or a horse, I see $250 stamped on its forehead because that's what it will cost me to provide them 100 bales for the winter. Take the cost of a bale of hay in your area, multiply it by 100, and virtually stamp it on the forehead of a cow or horse you are considering purchasing. If you can't provide the hay that animal needs for the winter, step away from that animal!
If you can bale your own hay, of course, you'll save money - after you buy the equipment. You'll either have to run it yourself or hire someone to bale your hay for you, another cost.
Buying hay for winter is a sacrifice, always, in trade for the rewards of keeping livestock. We owe it to them as their stewards to be practical and realistic with ourselves in choosing whether we can afford to keep them.
Writer Suzanne McMinn lives in Roane County, where she writes every day in her blog, Chickens in the Road, at www.chickensintheroad.com.