If he's already on alfalfa, adding a bit more wouldn't be an issue, but I would be very hesitant at feeding him straight alfalfa as free choice hay. IMO it would be much better to up his alfalfa a bit, and then add free choice bermuda, or something similar. I do want to say that obviously what you decide to feed is your choice, but just because one horse you know colicked because of a certain feed, doesn't mean that your horse will have problems. I have known a couple of horses that have died from colicked caused by eating too much alfalfa, and a horse that died of colic from bermuda grass, which got twisted up in his intestines, and yet I still feed my mare a mix of alfalfa and bermuda, and aside from a chocking episode, she's had no problems. Just something to think about. Again though, it is obviously your choice based on what you feel comfortable with, and what your horse does good on.