I don't know, but my buns say "yum yum" and so do my piggies! I get Oat, Wheat & barley hay (from TheHayExperts) and usually give them loads but now just put a large handful in a large dog bowl, rather than in the litter tray...only cos it is more expensive and I'm running low and they are out of stock
But my buns also have a selection of other hays too, so i don't worry...as long as they eat it!