Year-round here, beginning about 2-3 years ago-though some get a lesser amount in the summer.
Can't get shreds here, so it's pellets; buy from the store whose bag tag DOESN'T include molasses, but some have said that it ALL has molasses, so ???? I don't rinse it. I use warm water to fix it, year round, but lukewarm in summer, hot in winter, because it cools off fast in our winter temps! Feed it in the evening, concentrate in the AM, and of course, hay at each feeding.
I am sold on the benefits of beet pulp. I do feed Triple Crown Senior(alone)to my 28 YO mare; and mixed w/ TC Lite to several of the others...Senior has shredded beet pulp also, but I don't feed a LOT of it, and credit it with helping keep the Old Gal in excellent flesh!
Cost has escalated MIGHTILY here in the past year; last I bought was $18.95/50 lb.; when I began using it, it was @ $8.95/50 lbs.! Still, I believe it is a benefit to the horses in several ways, so will keep using it as I have been.
Margo