I don’t know about donkeys, but the cows will not eat the moldy bits, the goats won’t either, but then my goats hardly eat hay… they have a human bringing them tasty tree branches and picking ferns for the when they have to stay inside because it’s doing the “acid from the sky” (rain… goats hate getting wet). The cowsI'm curious, I've always heard it said that cows and goats and donkeys can eat moldy hay and it not hurt them. I do not mess with any of those so I've never really looked into if there is any truth in that. I do know giving moldy hay to a horse is colic waiting to happen. Someone I know lost their 15 month old colt by accidently feeding moldy hay a few years ago. Some may say we are obsessive over our hay. Besides trying to properly store it each time we cut into a bale we inspect it before feeding it out. Horses are always trying to find ways to kill themselves. The last thing we need is to help them on their quest by feeding moldy hay. The same goes for their grain, a few times we have opened a bag of grain to find it had mold in it. Those have been promptly returned to tractor supply.
Will sort through and toss out any moldy bits and eat what is salvageable. Horses are much more delicate I suppose or less discerning? A couple times they have broken into the barn and eaten things to excess like a bag of barley, and a bag of sheep texture… they will certainly gorge themselves given the opportunity, the cows won’t and I don’t think the goats will either. Given half a chance the sheep will merrily eat themselves to death. I like DH’s description of them “they look like actual crackheads getting a sight of their drug dealer when they see a person with a bucket”