Help how many acres of haulage to feed a horse

[Ajofitz]

I have 2 horses and 3 ponies at present and 12 acres over 3 fields. I was planning to set aside one field of 4 acres for growing haylage and keep the other for grazing and riding. Will this be enough to see the through the winter ALS we might be adding more horses so is there a general rule of thumb as to the area required to feed 1 horse weather permitting?

Thanks

Please excuse typo in thread