Paleo Phil wrote:  
Also, does anyone know the purpose of phytase in
ruminants, given that they can only handle small proportions of grains in
their diet--that is, did they adapt evolutionarily to digest SOME grain, or
do non-cereal grasses also contain phytates, just in smaller concentrations?
I was unable to find any information on this.


I don't know anything about it, but I would assume that if an animal is adapted to eating grasses, it will also be adapted to eating the seeds of those grasses, but the quantity of seed to stalk would be small.  Feeding the seeds without the stalks of the grasses should then cause problems as you describe.
gale