I feed pre/probiotics daily. Before I sometimes would have bouts of colic and diarrhea, but, to be honest, I haven't had EITHER since I added pre/probiotics to the diet. ::knock on wood:: I am NOT saying that this is the entire reason ... I could just be lucky. However, it's hard to ignore such a coincidence. I have been digestive problem free for 3 years and counting since adding them. Opti-Zyme is great. Smells good and the horses eat it and it isn't horribly expensive. I am not trying to be JLC/Activa spokesperson here, either, but if they help digestion, aid in nutrient uptake and prevent gastric distress to some degree, I don't see any reason not to feed them indefinitely, especially if you have senior horses that need better nutrient and mineral uptake.