Chicken grit is made of small, crushed pieces of hard stone, most commonly granite or flint. These tiny rock fragments serve as a substitute for teeth, helping chickens grind their food inside a muscular organ called the gizzard. There are two distinct types of grit, each made from different materials and serving a different purpose.
Insoluble Grit: Granite and Flint
The most common type of chicken grit is insoluble grit, meaning it doesn’t dissolve during digestion. It’s typically made from crushed granite, though flint is also used. Granite grit is roughly 70% silicon dioxide (the same compound that makes up quartz and sand), with smaller amounts of aluminum oxide, potassium, sodium, calcium, and iron compounds making up the rest. The key minerals in granite grit are silica, mica, and sand, all of which resist the acids in a chicken’s digestive system.
Because these stone fragments don’t break down, they stay lodged in the gizzard for extended periods. Over time, the constant grinding action wears the sharp edges smooth. Researchers examining grit recovered from chicken gizzards found that retained stones were noticeably smoother than freshly offered grit, especially in birds eating rougher, plant-heavy diets that put the gizzard to heavy use.
Soluble Grit: Oyster Shell and Limestone
The second type is soluble grit, most often sold as crushed oyster shells or limestone. Unlike granite grit, soluble grit dissolves in the digestive tract and gets absorbed as calcium. This makes it primarily a nutritional supplement for laying hens who need extra calcium to produce strong eggshells, rather than a true grinding aid. Because it dissolves, it doesn’t stick around in the gizzard long enough to do much mechanical work.
Many flock owners offer both types: insoluble grit for digestion and oyster shell for calcium. They serve fundamentally different roles despite both being called “grit.”
What Commercial Grit Products Contain
Basic commercial grit is simply crushed and screened granite sold in different particle sizes for chicks, pullets, and adult birds. Some brands add extra ingredients. Manna Pro’s poultry grit, for example, includes vegetable oil as a coating along with five different probiotic strains intended to support gut health. These added probiotics are a relatively recent trend in the poultry supply market, though plain granite grit without additives works perfectly well for digestion.
Grit products are typically sorted into size grades. Chick grit is very fine, closer to coarse sand, while adult grit consists of larger fragments appropriate for a full-sized gizzard. Using the wrong size can reduce effectiveness or, in the case of pieces that are too large for young birds, cause problems.
Why Chickens Need Grit at All
Chickens don’t have teeth. The gizzard is their only organ for mechanical digestion, functioning like a powerful muscular pouch that uses compression and grinding motion to crush food. Grit particles act as the abrasive surface inside this pouch. The gizzard selectively holds back large food particles, grinding them against the retained stones until everything is small enough to pass through to the intestines. This process works similarly to how teeth function in mammals.
Without grit, chickens eating whole grains, seeds, grass, or insects have a harder time breaking down those foods. Birds on a diet of finely milled commercial pellets or crumbles need less grit since the feed is already processed into small, soft particles. But any flock eating whole or coarsely ground feed, foraging on pasture, or snacking on kitchen scraps benefits from having grit available.
Natural Grit Sources for Free-Range Flocks
Free-range chickens that forage across varied terrain often pick up their own grit naturally. They’ll swallow small pebbles, coarse sand, and bits of gravel from driveways, paths, and rocky ground. A flock with access to these surfaces generally doesn’t need supplemental grit at all, because the birds instinctively select appropriately sized stones as they scratch and peck.
Flocks on soft pasture or fine soil are a different story. Dirt alone isn’t coarse enough to function as effective grit for adult chickens, so birds on grassy pasture without rocky or gravelly areas typically need a dish of commercial grit available free-choice. For chicks in a brooder with no outdoor access, some keepers toss in small clumps of grass with dirt still clinging to the roots, giving the chicks access to tiny natural grit particles along with something interesting to pick through.
Choosing the Right Size
Grit size matters more than the specific type of stone. Chicks under eight weeks old need very fine grit, sometimes labeled “starter grit” or “chick grit,” with particles about the size of coarse sand. Grower-sized grit suits birds between roughly 8 and 16 weeks. Adult grit, with pieces up to the size of a small pea, is appropriate for fully grown hens and roosters. Offering grit free-choice in a separate dish lets birds take what they need. They’re good at self-regulating their intake and will ignore it when their gizzard already has enough.