If he is in good weight and can eat hay then why did you buy the alf cubes in the first place?
I prefer to use the pellets over the cubes. A lot of horse choke on the cubes. Alf pellets/cubes are usually used as a long stem fiber source (hay) for a horse who has limited or no teeth and cannot eat hay, or to add calories to a thin horse who needs to gain weight or needs more calories than the feed can provide to maintain weight.
Alfalfa is also used to buffer stomach acid in a horse with ulcers.
Personally, I would drop the sweet feed, get a quality RB (to provide min/vit), and feed him at least 2% of his body weight in hay split into multiple feedings a day.
Sweet feed (corn, oats, barley, etc) and other high NSC diets have been proven to have neg effects on horses such as laminitis, ulcers, hindgut acidosis, IR, founder and many more.
IMO, theres really no need for the alf cubes you bought. You're horse looks good. Alf is nice in the aspect that you can feed as much of it a day as nec to keep weight on a horse. I have fed anywhere from 1lb to 8lbs of alfalfa a day for one horse. It just depends on the individual horse and it's needs.
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