If your older horse is having difficulty staying in good condition, you may try adding beat pulp mash or corn oil to its diet. I’ve never fed rice bran, but many people recommend it. Because older horses might have very worn down, or missing teeth it’s important that the feeds be easily chewed. Hard large pellets, hay cubes and course hay may be difficult for your senior horse to chew. Not only will it not be getting the nutrition it needs, but there is a greater danger of choke. Some very old horses may need all of their feeds made into mashes (but not bran mashes). I’m not fussy about pelleted feed and prefer to feed it dampened to horses of any age.
Some senior horses become over weight, especially if their workload decreases. Feeds may need to be regulated, being sure that they still provide good nutrition, while not adding to your horse’s weight. You might consider a vitamin/mineral supplement, along with good hay or pasture. Weight gain can be a sign of health problems too.