Grit (for chickens)

Chickens have no teeth, so they cannot chew. Instead they swallow food whole and grind it down inside a muscular part of the stomach called the gizzard. To do that grinding, a hen needs grit. There are two different kinds, and they do two completely different jobs.

Flint grit (for grinding)

Flint or "insoluble" grit is hard, sharp pieces of stone that stay in the gizzard for weeks. As the gizzard muscles contract, these stones rub against the food and break it up, doing the work that teeth do in other animals. Without it, a hen struggles to digest grain, pellets and tougher plants.

Birds that range over soil and grass often pick up small stones naturally, so a free-range flock may find some of their own. Even so, it is sensible to offer flint grit as well, especially over winter or for hens kept on a hard run with no access to bare earth.

Oyster-shell grit (for calcium)

Oyster-shell grit is "soluble" — it dissolves in the bird and is absorbed rather than staying in the gizzard. It is really a calcium supplement, not a grinding aid. A laying hen puts a remarkable amount of calcium into each shell, and if she runs short she lays thin, soft or shell-less eggs, or starts robbing calcium from her own bones.

Laying hens, especially birds at point of lay and older ex-battery hens, have a high calcium demand, so oyster shell matters most for them. Crushed, baked eggshells can top this up, but a bag of oyster-shell grit is the simple, reliable option.

Offering grit free-choice

The easiest approach is to offer both kinds free-choice, meaning you put grit out in its own small container and let the hens take what they need. They are good at self-regulating: a bird will eat more when she needs it and ignore it when she does not.

Most UK feed shops, agricultural merchants and garden centres sell "mixed poultry grit", which already contains both flint and oyster shell, so a single bag usually covers both jobs. Keep it in a separate pot or a small wall-mounted dish rather than tipping it into the feed, so it stays dry and clean and the hens can choose. A bag lasts a small backyard flock a long time.

Two quick notes. Grit is not a substitute for proper feed — it works alongside layers pellets or mash, not instead of them. And growing chicks and non-laying birds need flint grit for digestion but very little extra calcium, so save the oyster shell mainly for your laying hens.