Mine have blocks, loose minerals, grain and alfalfa, and they still eat dirt! I don't know what else to do for them, so I just let them eat dirt. The horses are the same, they get daily vitamins and should be all good, but I see them eating dirt on occasion too. I figure, if its not a constant thing, or a huge amount, its ok, its not like there is anything I can do about it. I suppose I could get them blood tested when I see them doing it, but I can't afford that.