You are trying a shotgun approach to this and need to start over with the basics. Hay makes up the majority of his diet. Not all hay is equal. Have you tested it? Simple $25 test. If the hay is at all mature, it will be low in calories and he can eat it all day and get just about nothing out of it. Assume he needs 20 Mcals a day just to maintain. Feeding average grass hay that would equate to about 25#. Does he eat that much? If he will not eat enough hay to maintain than you need to add higher caloric feeds to make up the difference. Alfalfa, lespedeza or perennial peanut hay would be the first thing to try. Alfalfa pellets can be a substitution but they are often made with lesser quality hay (stemmier, more mature, less calorie dense) plus you pay about twice more than baled alfalfa. Alfalfa will have about 10% more calories by weight. Feeding him 50/50 gives him the boost of extra calories and protein plus grass hay to keep him busy and warm at night. Beet pulp has slightly higher calories than alfalfa and is easily digested but not all horses readily consume it. If he were lacking teeth, than it's a no brainer but chewing is not a problem. Also for the price, I want more return on my $$, (You are paying $1000/ton for BP). Adding rice bran or vegetable oil will give you the most concentrated calories (5x grass hay) but getting them to eat it can be messy and a losing battle. Adding senior feed, barley, oats or any other concentrates will add calories but what are you doing to the balance of the diet? No where did I read vitamin/mineral supplement (no, the red salt block out in the pasture does not count).
Start with small changes. If he's standing around waiting for you to feed goodies instead of eating his hay, you've lost that battle. I would take all concentrates away and work him up to half grass half alfalfa hay. Offer a free choice vitamin/mineral blend (ADM Gostrong and Progressive Nutrition are my go to but even an average mill 12:12 will help) Give him a month and see if he maintains or gains. If he needs more, I would first go with the senior plus 1/4 C oil per feeding.
Just like with chickens, a little bit of this and a little bit of that when feeding horses usually cost more in the end without the results we are looking for.
BTW, 19 is not old. You are seeing muscle loss from the lack of exercise that makes thing look worse. He is at that age where he is less efficient converting his feed so adding a pre/probiotic won't hurt and some extra protein will help maintain muscle,
Start with small changes. If he's standing around waiting for you to feed goodies instead of eating his hay, you've lost that battle. I would take all concentrates away and work him up to half grass half alfalfa hay. Offer a free choice vitamin/mineral blend (ADM Gostrong and Progressive Nutrition are my go to but even an average mill 12:12 will help) Give him a month and see if he maintains or gains. If he needs more, I would first go with the senior plus 1/4 C oil per feeding.
Just like with chickens, a little bit of this and a little bit of that when feeding horses usually cost more in the end without the results we are looking for.
BTW, 19 is not old. You are seeing muscle loss from the lack of exercise that makes thing look worse. He is at that age where he is less efficient converting his feed so adding a pre/probiotic won't hurt and some extra protein will help maintain muscle,