If I want to supplement with calcium, is there any reason why I couldn't use crushed up calcium pills intended for human consumption? My birds are generally healthy but I've recently noticed a few porous looking eggs and a few thin-shelled eggs. They have never showed any interest in the oyster shell that I provided for them and they do free range every day so I figured they'd pick up what they needed while they were out and about. They are fed good quality layers pellets or layers mash and I give them a few handfuls of corn once a day (shared amongst 25 birds)....