Give your chickens some extra bite!
Chickens don't have any teeth, so in order to extract maximum goodness from the food they eat they need grit. Not just any old grit either, a hard sharp flint is best - of about 3-5mm diameter (like the ones used in stone age dentistry). This handy tub of mixed grit also contains soluble calcium (in the form of oyster and other sea shells) which will ensure your hens only lay the robust egg shells like the ones your grandfather has probably told you about. This packet would last two hens a couple of months, just add a handfull to the feed once a week.