I think its nearly impossible to feed a youngster the correct amount of protein in their diet without using a hay that is at least partial alfalfa. I have a weanling colt that is on alfalfa, beetpulp, and a handful of long stem soft timothy hay. My other horses are 4 and 11, and during show season, when they are working, I do give them an alfalfa timothy mix. Right now, they are both on straight timothy. To be honest, both are easy keepers, and get hefty on alfalfa if they aren't working. With going into winter, I like to be able to feed a higher quantity of hay to help keep them warm, but don't want them obese either. With them idle, I can feed way more timothy than alfalfa without them getting too too fat. Come March, everyone will go back on at least alfalfa mix, if not straight alfalfa.