Oyster shell grit is a staple part of the diet of domestic poultry. But to the newcomer to backyard hens, feeding oyster shell grit to chickens may seem strange. After all crushed shells and stones have no nutritional benefit for your birds or do they?
In this article, we will take a look at what oyster shell grit is, why chickens need it, and how you can feed it and use it effectively for your flock.
What is oyster shell grit?
Oyster shell grit is a pre-packaged mixture of oyster shells and grit. Grit and oyster are in fact two different products that have distinct purposes and benefits for your hen.
- Grit, also known as insoluble grit, or flint is a mixture of small stones to aid the digestion of food. It is made from crushed stones like granite, or quartzite and can be graded for the maturity of your birds. Some owners also use sharp sand with chicks that also contains small stone fragments.
- Oyster shells and sometimes limestone or other soluble stone are a source of supplementary calcium for your hens. The shells of oysters are ground down to a manageable size for hens. This is typically a particle size of around 2-8mm. They are made up almost entirely of calcium carbonate (95%) which meets the calcium requirement of laying hens. In addition, beneficial minerals like sodium, magnesium, iron, and copper, are also present too and are absorbed by the hen as the shell fragments dissolve in the digestive tract.
From beak to vent: Quick anatomy of the digestive system in chickens.
Knowledge of the chicken’s digestive tract is key to understanding just how essential oyster shell grit is to hen’s ability to break down its food. Chickens do not have teeth and therefore lack the ability to chew their food, breaking it down for more efficient digestion. They therefore also require an alternative mechanical method or breaking up their food.
The main structures of a chicken’s gastrointestinal system are:
- Ventriculus or gizzard
- Small intestine
- Large intestine
For the purposes of this article, we will focus on everything from the esophagus to the gizzard.
When chickens gulp down their food, it passes down the esophagus to the crop. This bag like pocket in the food pipe of the chicken is able to hold food and water for digestion later on. It is thought that the crop allows chickens to feed quickly when they are in an environment that has predators and get to safety to digest their food.
Food can build up or become impacted in the crop. This is known as a blocked crop. An impacted crop that is not promptly cleared can rot and become sour and even block off a hen’s windpipe and cause death. A hen with an impacted crop will often try to eat and drink water to move on the blockage which can be felt like a firm ball in the neck.
Grit is a key part of alleviating this impaction. Granite grit, olive oil, and massage can be used to help break up the lump and get things moving again. Separate an affected bird and start this regimen. If the blockage does not clear you may need to induce regurgitation.
Food then passed from the crop to the proventriculus or stomach which produces the digestive acids and enzymes necessary for digestion to commence.
The chicken’s alternative to chewing
Up to this point, the food has moved along unground, but it is in the ventriculus or gizzard, that food is ground down in earnest. This unusual muscular bag of an organ is present only in certain creatures, including worms and fish, which like the chicken, lack the ability to chew.
It has a thick, undulating lining that covers the two sets of muscles that do the work of grinding up the food so it can be moved on to the small intestine for absorption.
Gritty work in the gizzard!
This is where grit comes into its own. Free-ranging birds would typically pick up small stones and gravel which pass from the crop to the proventriculus. The acidic environment of this mini stomach softens and wears the stones with the food so that in the gizzard, they work as ‘teeth’ in the grinding process. The stones do their work in the gizzard until they are worn down enough to be passed further down the digestive tract.
Grit will improve the efficiency of its feed
Making an appropriate quantity of grit available to your hens that are kept in a run or coop ensures that their bodies can optimally perform this vital function and ensures that they get every bit of nutrition available from their feed.
Soluble grit helps the modern laying hen gets enough calcium
In times past, backyard hens foraged and scraped a large part of their diet and produced eggs sporadically. Contemporary breeds are expected to deliver up a fresh egg almost daily which places heavy demands on a layer hen’s system.
Therefore, it is important to ensure that you supply adequate nutrition to meet the requirements of daily egg production. Calcium in particular will not only be needed for the hen’s body but also the formation of eggshells of suitable hardness.
A typical layer hen consumes around 5,000mg of calcium daily and just under two-thirds of this quantity (3,000mg) goes to the egg. An eggshell will require 2,000mg and the remainder goes to the yolk and albumin.
Just in time egg production leaves limited calcium stores for the hen
The formation of an egg occurs throughout the day starting with the inner yolk and albumin and rounding off with eggshell production in the afternoon and evening. At this time the hen will draw on food consumption during the day to release the necessary calcium for this task. If there has not been adequate calcium in the diet, the hen will draw on bone reserves to finish the job.
Bone reserves are limited and the hen can only acquire 100mg of calcium per day in this way. This is why oyster shell and limestone are so important to hens. Without enough calcium, harmful deficiencies quickly become established.
Symptoms of calcium deficiency in backyard chickens
As an owner of chickens, you should always remain vigilant for signs of calcium deficiency in your hens as it can be readily corrected. Alongside calcium, deficiencies of phosphorus and Vitamin D are linked and may produce similar symptoms.
- Growth reduction
- Chickens eating their own eggs (they may be seeking calcium to fulfill their requirements)
- Rubbery legs
- Seizures and paralysis
- Eggshells in calcium-deficient hens will also be extremely weak.
Feeding your chickens the right kind of calcium will boost their stores
To keep up with demand your hens need supplemental coarse calcium stores like limestone and oyster shell. Because they have a large particle size that is ingested whole, they will break down slowly in the gut and release calcium to the hen over time. This means that the hen has absorbed calcium available for the time of peak demand in the even hours of eggshells formation, even when feeding is not taking place.
How to feed your hens oyster shell grit.
Your hens will need both soluble and insoluble grit to ensure that they can both grind their food and absorb adequate calcium. Grit and oyster shells are usually combined in a supplement you can buy and add as needed to your hens’ food.
Free-access is considered a good way of ensuring that your hens will all get enough of an oyster shell and grit mixture. A feeder can be set up with a plentiful supply. Hens are known to take as much as they require as they need it.
Alternatively, a quantity of the mixture can be added to their ration. Adding oyster shell grit directly to chicken feed is controversial but usually, it can be mixed in (thoroughly) at a ratio of one pound to every 20 to 40 pounds of feed. It is advisable to also offer added grit and shell on the side in case some birds need more.
Most owners report that chickens will simply pick out what they need anyway.
Oyster shell grit should be fed to your hens all year round and continued whether or not they are actively laying and even through their annual molt.
It is important to feed chickens the right type of insoluble grit. Free-ranging birds will naturally peck up small pebbles and rocks to do this work. Most grit will range in size between 2 and 5mm to ensure birds of all sizes can infest enough grit.
Chicks and pullets will need flint of appropriate size once they leave the brooder. If it is introduced too early or is too fine, like sand, it can cause impaction.
Q. Do I need to give oyster shell grit to free-range hens?
A. It is wise to not be complacent about what free-range chickens are taking on board and ensure they have access to both a complete feed and a decent supply of grit and oyster shells. This is because they may not be able to find adequate soluble and insoluble grit to meet their needs.
Q. I feed a nutritionally balanced feed with added calcium. Why do I need to provide oyster shell?
A. Many premium poultry feeds are fortified with calcium. However, a hen’s demand may outstrip supply later in the day when the majority of their food has been absorbed. This is why large particle size insoluble grit is vital. It is a slow-release form of calcium. Also, the level of calcium may vary depending on whether the feed is for laying hens or not.
Q. Can you feed your hens eggshells to increase calcium?
A. Yes. Many owners add cleaned and ground up eggshells to their poultry feed. But it is important to note that they usually cannot fully meet the needs of a laying hen. Also, any calcium made available from the eggshell is quickly absorbed. The sustained release calcium from oyster shell or limestone is of much greater value. Remember that hens actively pecking and eating their eggs may be deficient in calcium and need greater quantities in their diet.
Where to buy Oyster Chicken Grit
How much oyster shell and grit should my hens be getting?
For a backyard flock of hens, vast quantities are not necessary. A 7-pound bag of oyster shell grit should last a small flock the best part of a year. It also stores well with no spoilage if left out.
Are there any causes of soft eggshells other than low calcium?
- Hot weather can lead to a run of soft-shelled eggs as your hens will tend to eat less when it is hot. Normal hardness will recover naturally when they cool down.
- Efficient layers; with some breeds of hen producing well over 300 eggs in a year, a good layer may simply be pushing out the eggs quicker than the shell can fully harden.
- High phosphorus can be an underlying cause of a softshell an excess of phosphorus inhibits the laying down of calcium in shell formation.
- Old age will lead to a decline in egg quality, including the thickness of the shell. As birds age this ability to mobilize calcium from the bone declines. The eggs are also larger in mature birds.
Soluble and insoluble grit perform critical physiological functions in chickens and therefore are a priority for your backyard flock. Making sure that all your birds have suitable access will ensure that not only their food is properly digested, but also the calcium needed for firm eggshells and good health is in plentiful supply.