I feed the BBB oaten hay but only because I get it for free and I know exactly what has been done to it from seed to baling. BEB, maybe your hay was baled when it was still a bit too moist hence the mould? If I had to pay for hay I really don't think I would have a horse. In the summer when feed gets low I will buy the occasional bale of meadow hay a just put it in the paddock. BBB chucks it about and eats it then the sheep come in and clean up the rest.