If a bale is unwrapped it needs eaten up within 4 days, less is better. 50 Swaledales or 40 Texels will eat a bale in 4 days, or round about 12 cattle in 2 days.
As Ina says, it's the exposed face that spoils, so if you can think of a way of slicing it you could maybe eke it out a bit that way.
If it's been made for some months, the slicing approach would probably work - slice off enough for one day, the next day slice off what was exposed yesterday and feed that, and so on.
But if it's very recenty made there's a risk of the wrong sort of bacteria getting in and causing the wrong sort of chemical reaction - I wouldn't take that risk, I would find someone to share it with you.
HTH