Beet pulp is good for putting on weight, but it is pretty high in calcium so watch out you don't overfeed it, to youngsters in particular. I find that beet pulp and bran as a combination work well, as both are high fibre, easily digestible, and the high calcium in the beet pulp is balanced out by the high phosphorus in the bran (plus bran is great for those with slight digestive sensitivities). My conditioning feed always consists of alfalfa chaff, beet pulp and bran, and I find it cheaper to buy the straights and mix them than buying a pre made conditioning feed.
I personally feed human grade wheat bran, and in small amounts (it is very high phosphorus, but in small amounts this helps balance out the high calcium in both beet pulp and alfalfa chaff and hay). Wheat bran is higher in easily digestible calories than rice bran, but if you aren't sure about balancing your phosphorus levels then I'd recommend rice bran, as manufacturers tend to balance the calcium phosphorus ratios in rice bran as well as adding some fatty content for weight gain. If you're going to introduce a small amount of bran to the diet, do it slowly, as if you introduce it too quickly it can act as a laxative.
Off the top of my head I can't remember the weights I use (will have to check my feed board!) but my feed equates to roughly a scoop of alfalfa chaff, a quarter scoop of beet pulp (before soaking) and a 100ml scoop of bran, twice daily.
I used Purina Strategy and rice bran to keep my hard keeper up to weight! It was a great combination that packed on pounds without making him hot (we had previously tried Triple Crown Senior- great feed but it made him high!)
Best of luck!