Hi Becky,
Beet pulp is right on the edge between being a forage (fiber content 
greater than 18%) and an energy feed (fiber less than 18% and protein 
less than 20%).  Beet pulp has a fiber content of 18.2%, a protein 
content of 8.9% and an energy content of 2.33 Mcal/kg, which is lower 
than oats, bran (or any other grain) and only slightly higher than early 
bloom alfalfa.  So it does have some very nice uses in horse rations, 
specifically in horses which don't need a ton of grain, but maybe could 
use something to occupy themselves with during the day (here in So Cal, 
stalled/bored horses are common, so this is a factor).  The Ca:P ratio 
is also good---one of the problems with many grains is that provide alot 
of phosphorus, sometimes a problem if not balanced with the calcium.  
Beet pulp already has a Ca:P ratio of 7:1, so if you're feeding it, you 
don't have to worry about the ratio.  The other nice thing is that it 
provides more energy per kg than does alfalfa (and a significant amount 
more than the other hays) without providing alot of protein (that's 
good).  It also provides a nice balance of .54% lysine (the amino acid 
you're most likely to be deficient in--not as much lysine as alfalfa, 
but quite a bit more than the other forages, and almost the same as 
wheat bran without the excess protein or phosphorus).
In short, beet pulp has ALOT of advantages without alot of the 
disadvantages of some other the other feeds.  The one big drawback, and 
you CANNOT ignore this, is that you must soak it before feeding.  Patty 
Chase has already posted the problem with impaction and blockages, and 
described how to soak it.  If you're willing to put up with the minor 
inconvenience, then it's a very good feed.
Hope this helps.
Susan Evans