Wow, well, we have a complex feeding program. We have 23 horses which range in age from 9mths to 28 years.
The older horses, who are harder keepers get 2 scoops Sr feed + 1/2 scoop alfalfa pellets + 1 cup Moorglo (a weight builder) + vitamins+ probiotics 2x daily Some of the Senior citizens get some hay, some don't depending on their teeth (or lack thereof

) They don't really NEED the hay because the SR feed is a complete feed, but if they can chew and swallow it, they like it, and it is a good mental stimulation. Oh they also get MSM for their joints.
We feed M-G feed, a semi-local feed company in Texas. It is a decent feed for the price. There are better feeds out there, but many that are definitely worse. This one is the most similar to Stradgey which is made by purina, but cost less $$
Due to the hay shortage in Tx we also supplement our hay with beet pulp. This is what we feed our "main" herd.10 dry scoops of beet pulp (then it is soaked) add to that 12 scoops of 12/8 (12% protein 8%fat) + 2 scoops alfalfa pellets, + vitamins + hay once a day. This feeds 12 horses who are out on aprox 20 acres pasture.
The babies get 1 scoop 12/8, 1/2 scoop 14/6 and 1/2 scoop alfalfa pellets. + vitamins 2x daily They have their own pasture. (a couple of acres) They do not get beet pulp. They also get hay.
Any horse that is underweight, will get fed seperately, and have alfalfa pellets+ moorglo + beetpulp+ vitamins + probiotics added to their feed 2x daily plus free choice hay + pasture.
Mooreglo is a ricebran derivitive that is a weight builder. We have tried many types/brands weight builder and this seems to work the best for us.
Probiotics are a microorganism added to feed (similar to yougert cultures) which help the digestive system utilize the feed it is getting. You can buy this in a paste (similar to a wormer) or a powder that you add as a top dressing. This is good for older, underweight, and babies. (for the babies, use the paste to help them not get the scours)
Beet pulp can be used as a hay stretcher. It is mostly a high fiber food. Some people use it as a weight builder, but I haven't seen that happen in my horses. I can't remember the protein/fat content. But it does have some protein and fat in it. (not much though)
We use alfalfa pellets for two reasons. 1) It helps with the lack of hay/fiber content. 2) it is a higher protein feed (something like 21%) and protein builds protein.