I've used beetpulp for the longest time with my ponies. I found that it worked for some of them, but not as a steady weight gainer & maintainer for others. I got my Standardbred mare this past June, and she was very underweight.. So, like many other underweight horses I brought home in hope of saving, I thought I would do research on what I could really feed her to fatten her up fast as oppose to beetpulp and other costly performance feeds.
Purina sells a brand called Trimax - and it's the most fastest weight gainer/maintainer I have ever used! It contains 3 major fuel sources that are key features in weight gain - fat, starch and fibre (BP obviously) as well as it contains Omega 3&6. I think it's the greatest feed - everything is combine into one with equal amounts, so it's not like you have to 'dick' around with trying to measure stuff out, and wonder if you really are feeding enough.
I also feed Krunch - by Masterfeeds.. Another weight maintainer plain cube.
*My typical feeding schedule for this mare is: 2 average size scoops of Trimax, 1 scoop of rolled oats (I feed this for energy, as she is up there in age), 1 scoop of Krunch, 2 tbsp of Corn Oil - for a healthy coat, and of course, carrots!
Here's the websites for both brands:
Trimax:
http://www.agribrands.ca/Screens/TriMAX.aspx
Krunch:
Horse Krunch cubes