i was watching my chicken run around and found one limping so i inspected it. the left foot was swollen between the toes and ball of the foot, no external injuries evident, no mites, scales looked good on the feet. the other chicken, thinking one was getting a treat and they were not, started to crowd around and i noticed half of the others had their left foot starting to swell. the only thing i can think of is 3 days ago while pouring out some oyster shell the bag ripped and dumped about 10lbs of shell onto the ground, the next day it was all gone. could the swelling left feet be caused by to much calcium and what can i do to help them.