I would stick with the cubes if horses are not getting much in actual fiber from hay or grazing. The digestive system needs that "scratchy" stuff going thru. Even fed wetted, cube fiber is rougher than the alfalfa pellets or wet beet pulp type feeds. Does different things for the benefit of the equine, though pellets and cubes are "both" alfalfa.
My old horse got a better bloom to her when I added wet hay cubes, though they were not alfalfa. She liked the roughage going thru, even if it was soaked cubes. She was not able to chew and swallow hay, though she did make hay spitwads (quidding). Results were visible, even though I thought she looked pretty good before the hay cubes! Just brighter. And she enjoyed her wet cubes too, something NOT a sloppy mush!
This link should provide some clarification. The pellets are still roughage, no it is not going to be at "long" as the cubes because it is more chopped up, but it is still fiber. I would just look at the guaranteed analysis on the bag and feed accordingly.
This article also talks about hay cubes and pellets being an adequate form of roughage.
Years ago here where I live there was a big outbreak of botulism in horses fed hay cubes. The story was the hay cubes are pressed with no heat processing and traps toxins which created this issue.
Unlike pellets that are heat pressed or bale hay that is open to air that will kill the toxins that occur in hay cubes.
I don't really have much more infomation but know 30 some years ago all we fed was hay cubes (loved them) but feed only bale hay or pellets now because I worry in our area the cubes could create a problem.
Train like you have never won and show like you have never lost!!!
I use both My horse has not so great teeth so I do use the cubes as a mid-day lunch, soaked with TC senior because they are considered longer stem fiber. However on days when I don't have as much time to soak, I started to use pellets mixed with his a.m. and p.m. feed, and I use some mid-day mixed with the cubes so I can at least get him started on what has already softened. Interestingly, since I began this, he is not only holding his weight for the first winter ever, but he is gaining weight!! He has never looked this good in January!
If your horse is getting enough other fiber, the pellets are easier IMO. They soak faster and my horse seems to like the taste more.
As for getting your horse to eat them, I just mix TC senior with it and make a mash.
I feed free choice hay along with the pellets, that way I'm not worried about the fiber. For me, it's way easier that way. Only time I'm interested in cubes anymore is if I have a horse that I worry about getting some water into for any reason, or if I had a horse that couldn't chew it's hay properly. If I couldn't get pellets, I'd get cubes instead but I much prefer the convenience of the pellets!
I feed both too. I feed it as a carrier and disguise for sups, but also as a way to keep my rough boarded horses hydrated in freezing weather. I feed both because I find they make a great mash consistency. I am not worried about fiber right now.
I don't like pellets alone, they make a gloppy soup and my oldster is such a pig he gets impatient with food with no "chew factor" and tries to inhale/gobble/inhale really soupy foods. He even choked once on a bucket of soup. My younger gelding loves to play with soup and splashes it everywhere. 50/50 cubes and pellets though seems to be perfect.
Scooping cubes is a huge pain though. I find a chinese food wonton soup container (one quart round plastic container) works better than a traditional plastic scoop. My friend says the best of all is one of those big kitty litter scoops. Scooping pellets sure is a lot easier, I will say that. I do curse the cubes every morning.