no mollasses added(95%sugar free), then a patented process, then heat treated, then flaked giving a much larger surface area to absorb water leading to rapid water absorption and less soaking time-type speedibeet into google and get a much better description than this
my little pony was almost skeletal before we put her onto speedi beet (condition score of just under 2). it has helped her gain weight slowly and at a consistant rate. i'd recomend speedi-beet for laminitics and those not wanting really quick weight gain.
i feed my laminitic cob speedibeet in small quanitities but would use ordinary sugar beet for those you want to gain weight, plus perhaps barley rings. I used that on a tb and it kept weight on him during winter very well.
If you are wanting to put weight on, why do you think beet pulp? This is a forage (high end admittedly) not a weight gain product and therefore should be thought of as the base of a feed to ensure that the horse doesn't bolt his food and to ensure the gut works at digesting properly. If you want weight gain you need calories - that means either grain or oil. Or simply increasing the amount of food that your horse has access to - the simplest being more good quality hay.
Beet pulp is around 2.2 to 2.3 MgCAL per Kg about the same as Lucerne Hay - but you are only feeding a very small amount - remember that's 2.3Mcal\kg DRY weight. So if you soak a couple of cups it fluffs up to a good quantity but that bulk doesn't = calories because all you've added is water.