I dunno, that's how they baled them for horses back when I had horses. (From the time I was 12 until I was 17½) Anyways, I didn't bale it, I just went out in the field and loaded it on the trailer and from there, into the barn. Now, hay for cattle can get all moldy and icky, the cattle don't mind. Moldy hay will make a horse pretty sick, if not kill them.
This was fescue hay and it was dry. If it was wet enough to mold it would go thru a heat and possibly catch fire. Farmer lost a corner of a barn here a couple years ago to that. He said he kept smelling smoke all day and just couldn't figure out where it was coming from. Just before leaving the area for home he saw flames and called the fire department.
If we ever put up any that daddy thought might have to much moisture, I had to test it. Everyday for a couple of weeks I would go out to the barn and dig down in a stack. I'd take out a bale and cut it open and feel it to see if it was hot. Found a few that got pretty warm but never any close to catching fire.
Now they cut hay with a mower that will windrow it and the baler comes right behind the mower and bales it. Then they pick it up on a machine and wrap it air tight in plastic. It goes thru a heat and pickling process like sillage. Stinks to high heaven but the cows love it.