I did a good ten days or so of pretty intense research on equine nutirition before I even brought the horse home which is why I have the addition of the rice bran pellets and the pre/probiotic.
In all this, however, the point may be moot. The extra turnout time he is now getting, and had only just started when I initially posted, seems to have settled him. Will see in any case.
I DO appreciate the advice :)