Laying hens need soluble grit or some other source of supplemental dietary calcium, but pretty much all chickens of either sex and all ages need insoluble grit for digestion.
Chickens don't have teeth, and they swallow corn and seeds whole. Their digestive system is not like ours. First the food goes into their crop. That’s basically just a bag for temporary storage of the food (that’s handy for filling up in the evening before a long winter’s night), although the food does get softened a bit in the crop, helped along by enzymes from the chicken’s saliva.
From there is passes to the proventriculus, which adds pepsin and hydrochloric acid, but the food doesn’t stay here long.
The real job of breaking up the food into digestible particles is done in the gizzard. It’s a very muscular organ – in fact it can exert a pressure of up to 500 lbs per square inch. But she helps that along by swallowing little stones that stay in her gizzard. The food stays in the gizzard for a few minutes or hours while the gizzard muscles work at it, grinding it up against the grit or stones, and then the food continues down to the stomach with its digestive juices.
So chickens need little stones in their gizzard – that’s insoluble grit. Oyster shell is not much good for grinding up food – it’s too soft and anyway it eventually dissolves. Chickens can digest their food better, and therefore be more economical to feed, if they have some grit in their gizzards.
Commercial chicken mash or crumbles or even pellet food is soft and crumbly enough to be broken up purely by the muscles of the gizzard itself. But as soon as you feed your chicken anything else, like cracked corn or grain, or even grass or leafy things, their gizzard needs something to grind against. Even baby chicks.
Commercially available insoluble grit is usually granite or flint. Or you can make sure your chickens have access to plenty of gravel, crushed rock and small stones. Either way make sure your chickens have access to insoluble grit so they can most efficiently digest their food.
So there is a difference – soluble grit, made from oyster shell or egg shells, which laying hens need as a source of calcium, and insoluble grit, consisting of fine gravel or rock particles, hard enough to digest the food in the gizzard, which is essential for pretty much all chickens of all ages.
For more fascinating facts, hints and tips about caring for your chickens, and the sheer pleasure of chickens, subscribe to my channel: Chickens in my garden - New Zealand
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