How many flakes of hay does a 20 year old horse need per feeding?

it depends what you are feeding and how often. if you are feeding straight alfalfa and feeding twice a day, i would do a flake in the morning and one in the evening if the horse is healthy. but if the horse is having trouble keeping his weight up i would do a flake in the morning with a supplement or a grain and two flakes in the evening. gradually wean him onto this schedule though because if you start right away you may risk him colicing beings his system is not used to the extra feed.