if it goes mouldy, it wasn't dry enough when packaged. Happens more than you know
After 30 odd yrs sourcing decent hay for my horses I definitely agree with that.
Any hay you buy is likely to be anything up to a year old. Most farmers only cut once a year, sometimes twice. If it was cut, dried, baled and stored properly it won't be a problem.
It will lose it's nutritional value as it gets older though. I am currently feeding my highland pony 18 month old good quality hay as nature designed her to live off of sparce, not to rich grazing.
As above, it's all in the storage and initial drying as to how well your hay will keep.
(and WOOO HiPos are the BEST, my share is HiPo X)
They are aren't they. For those of you that don't know them - just think 5' guinea pig.