Wow, big difference in the American and British pronunciations--kind of like aluminium. And neither is how I speculated, which was gig ar' i um (hard Gs).
gIj' rE um
No, the grinding is in the gizzard, NOT the crop. I believe the question was whether or not you can get too much grit in the gizzard, filling it up with grit, and whether teh grit eventually passes through. Good question that I never thought of...