Oyster shell or soluble grit
Oyster shell grit, a source of calcium to help form strong egg shells.
In order to form strong egg shells, chickens require a certain amount of calcium in their diet. Most of an egg shell is made up of calcium. These days, with the research that has been done for formulated feeds (available as layers mash or pellets), it isn’t so critical to provide oyster shell grit because layers feeds contain sufficient calcium, however, it’s cheap and it’s easy to mix some in with the flint grit that they need above so it’s a good idea to provide some, in case they need more calcium. High production hybrid hens are capable of producing a staggering number of eggs in a year on very little feed (known commercially as the ‘conversion ratio’) so they are more likely to need the extra calcium to be able to produce the right number of eggs of sufficient quality.
If you can’t find Oyster shell grit from your local store, baked, crushed egg shells will do the same job – after all, they are mainly made up of calcium! Put them in the oven for 10 minutes to dry them out and crunch them up before mixing them in to your grit hopper.
Soluble or Oyster Shell Grit
The second type of grit you can buy is known as soluble grit or Oyster shell grit. This is usually ground up Oyster shells but can also be Cockle shells or limestone. Since egg shells are also mainly made up of calcium, it is also possible to grind up egg shells and feed them back to the birds. Oyster shell grit is larger than flint grit and dissolves in the digestive system, providing the bird with sufficient calcium to produce strong bones and good egg shells.
Modern poultry laying feeds usually contain sufficient calcium however there is no harm in providing some additional calcium in this way, especially if you like to provide some of your hens ration as household leftovers (mixed with layers mash ideally) in which the amount of calcium they are getting varies.
Birds that free range will usually pick up enough insoluble grit from the ground however there is no harm in providing additional grit for birds to take if they need it. Grit is usually best given to birds in a specially made hopper on an ad-lib basis. Soluble and insoluble grit can be mixed and you will sometimes find it is sold like this. If you don't have a grit hopper, it is also possible to put a handful of grit into the feed hopper with birds feed.