Poultry Supplements: Grit and Calcium

Most people who keep chickens already know the basics of necessary supplements. For decades, probably even longer, grit and a calcium source have been at the top of the list for poultry keeping necessities, both dependent upon the poultry’s access to natural supplementation.

It is thought by some that providing a good quality layer pellet will meet all calcium needs and additional calcium supplementation is not needed; however, we feel it’s “better safe than sorry” and provide a crushed oyster shell supplement at all times.

egg shell anatomy
From: http://www.pysanky.info/Other/Egg_Bioscience.html

An average sized egg shell contains approximately 2 grams of calcium, and a hen of laying age needs about double that (4 grams) per day in calcium supplement to properly produce eggs.1 To understand the need for calcium supplementation, it is important to fully understand the calcification process – the creation of the egg shell in the shell gland during egg production. Female birds have evolved a special bone feature called the medullary bone that allows them to store extra calcium for egg shell production. Under normal circumstances, birds carry calcium in their blood plasma to use with common biological functions, but that level of calcium is only available for a short period of time and is not a level high enough for calcification. Through special biological & hormonal functions during breeding season, female birds store extra calcium in the medullary bone and are able to quickly withdraw this calcium for the calcification process. This only occurs during breeding season, except in domestic birds that have been bred to lay year-round, in which this process continues the entire laying life of domestic poultry. While the medullary bone has a special regenerative ability, years of continued year-round laying can lead to calcium deficiency in other skeletal bones. “Medullary bone, unlike structural bone, is capable of undergoing rapid absorption and renewal. Unfortunately, resorption of structural bone also occurs causing the symptoms of osteoporosis (Whitehead, 2004). Osteoporosis is caused by a decrease in the amount of fully mineralised structural bone leading to bone fragility and susceptibility to fracture…”.2

Laying poultry may be able to obtain the needed level of calcium from their laying feed, but the form of calcium used in layer feed passes quickly through the digestive system resulting in a limited absorption time and insufficient levels for proper calcification. In a typical egg production cycle, the calcification process occurs in the early morning hours when chickens are roosted and not consuming feed. Limestone is a common calcium supplement, and many people offer egg shells to their flock, which is a good source of calcium. However, studies have shown that, overall, crushed oyster shell is a superior calcium source resulting in the best quality egg shell production. Crushed oyster shell takes longer than other supplements to pass through the crop & gizzard thus providing a longer period of calcium availability, better stabilization of blood calcium levels throughout the night, as well as helping to properly maintain the medullary bone for long-term laying.3,4

At our farm, some of our birds get to free range everyday, but due to breeding restrictions, some have to make do with large runs. While they do have access to large areas of ground, they may not have enough access to “grit”, and they certainly don’t have access to lots of bugs and other goodies that might provide extra calcium. Due to that limited access, our birds are provided free-choice access to our custom-mixed grit/calcium/charcoal at all times.


We typically use Manna Pro Poultry Grit (insoluble crushed granite) to mix with a quality oyster shell. Grit is required for all poultry consuming anything besides layer feeds, such as scratch grains, clippings, or food scraps. Commercial feed breaks down quickly in the digestive tract and typically does not require grit to properly digest. However, because poultry do not have teeth, they must have grit in their gizzard to grind what they have consumed. Without grit there is a high risk of developing impacted or sour crop (not just in the crop) due to things getting backed up and not passing through properly. Even pastured poultry should be provided grit to ensure there is proper sized grit particles for their consumption.5 Additionally, grit helps better digest and get the most nutrients out of what the bird has eaten.

As an added perk to our free choice grit/calcium, we also add a small amount of activated charcoal. For centuries, people have utilized charcoal as a detoxifier to bind toxins & harmful chemicals and prevent them from being absorbed in the body. Activated charcoal works through a process called adsorption where its extremely porous surface binds to toxins, chemicals, heavy metals, and more as it moves through the digestive system and is eliminated naturally. Activated charcoal should be used in moderation because, unfortunately, it can also bind to good chemicals and reduce nutrient absorption.6 We offer this in our free choice mix because we believe that our birds naturally know when and how much to consume.

Disclosure: Mo’s Mini Farm offers this information as a guide to poultry care and as an opinion based on the best reputable information available to us. We attempt to reference factual information from reputable books, websites, and scientific publications. We always encourage others to do their own research which is why we provide footnotes and references for you to utilize.

For overall information regarding all things chicken health related, we recommend The Chicken Health Handbook by Gail Damerow (2015, 2nd edition; Story Publishing). The following sections were referenced for the above information: “Medullary Bone”, pg 70; “The Calcium Connection”, pp 116-117; “Grit for the Gizzard”, pg 40; and “Tale of Two Stomachs”, pg 80.

1 “Nutrient requirements of egg laying chickens”,  2018 Poultry Hub: http://www.poultryhub.org/nutrition/nutrient-requirements/nutrient-requirements-of-egg-laying-chickens/

 2 M. M. Bain, Y. Nys, and I.C. Dunn, “Increasing persistency in lay and stabilising egg quality in longer laying cycles. What are the challenges?”, May 3, 2016; published in British Poultry Science, 57(3): 330–338. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4940894/#S0007title (May 23, 2016)

3 T. G. Taylor, “How an Eggshell Is Made”, March 1970; published in Scientific American, 222:88-95. https://accounts.smccd.edu/case/biol215/docs/eggshell.pdf

4 R. Meyer, R. C. Baker, and M. L. Scott – Department of Poultry Science, Cornell University, Ithaca, N. Y. 14850, “Effects of Hen Egg Shell and Other Calcium Sources Upon Egg Shell Strength and Ultrastructure”, August 28, 1972; published in Poultry Science, 52: 949-955, 1973. http://citeseerx.ist.psu.edu/viewdoc/download?doi=

5 Tiffany Towne, “Grit for Chickens: When in Doubt, Put it Out”, October 18, 2017. https://countrysidenetwork.com/daily/poultry/feed-health/grit-for-chickens-digestive-health-when-in-doubt-put-it-out/

6 Maat van Uitert, “Charcoal For Chickens”, November 7, 2016. https://www.hobbyfarms.com/charcoal-for-chickens/

Additional Resources:


Some of the links on Mo’s Mini Farm pages are affiliate links, which means that if you decide to purchase a product through them we will receive a small commission. There is no extra cost to you! This helps us to keep the information on the website free of charge and to support our farm adventure. Because we value our integrity in recommending products, we only recommend products we have purchased and used. We may occasionally provide links to a product we are considering or planning to purchase, but we will always be sure to clearly state this fact. For more information about our affiliate relationships please see our Affiliates Disclosure Document.

Double-Yolk Eggs Could Mean Trouble

Earlier this week, we thought we had a broody hen already occupying our most popular nest box in a largest flock. 20170414_174255Splotchy had set up camp and was sending out her broody sounding warnings anytime another hen came around. She is the only EasterEgger hen in the flock and lays a nice blue egg, and she is also the hen who sneaked hatching three fuzzballs late last summer. She’s relatively young – just coming into lay last spring, so we thought she’s just going to be one of those broody-every-time-you-blink kind of hens. Since we are in no short supply of chickens right now and anything she might hatch would be a real barnyard mix, we were not real interested in letting her continue.

Shortly after the discovery, we could hear a very loud egg song coming from the coop. Mama Mo mentioned to Papa Mo that Splotchy was already broody for this season, to which he inquired if that was her making all the noise (he rarely hears the egg song since he’s typically left for work when the hens get moving for the day). We discussed since she was broody she shouldn’t be laying and went about our work repairing another chicken hutch.

Later in the afternoon, Mama Mo noticed she was out of the nest box and used that opportunity to collect any eggs before Splotchy had the chance to hatch anything. Surprise! There was a gigantic blue egg in the box! No wonder she was camped out in there for so long and making so much noise! Not surprisingly, it was a double-yolk egg that most likely resulted mainly from upset to the coop arrangement for that folk.

This mostly young flock was overwintered in a storage-building-turned-barn, and we are trying to finish it out as a permanent coop. Unfortunately, many of the young pullets have already started laying for the first time, and we are scrambling (no pun intended) to get nest boxes and such prepared for them, resulting in lots of confusion and disruption to regular laying right now.

Now, we tell this story to explain about double-yolk eggs. Many people think they are cool and some even brag that their hen lays double-yolk eggs all the time. We feel that, not only from the hen’s perspective (have you heard them yelling when laying those giant eggs??) but from a healthy chicken perspective, it could possibly not be such a good thing. And here is why: it means the hen’s reproductive tract could be stressed &/or injured.

An egg is produced when ovum/yolk is released into the oviduct to go through the cycle of forming the egg that is laid. About an hour+/- after an egg is laid, another mature yolk is released to start its cycle which takes approximately 25 hours to complete. The entire egg production cycle is a finely tuned process that can occasionally experience a “glitch”. If there is a glitch in the cycle, multiple things can result, such as more than one yolk being released causing a double-yolk egg to develop. This particular glitch in the egg production cycle is typically the result of hormonal change or imbalance as young hens are beginning to lay eggs or as an older hen’s typical egg production cycle slows down. It can also be hereditary, and some cultures in other countries breed for this trait.

The double-yolk phenomenon is typically harmless and produces perfectly edible eggs, but it does usually mean an extra-large egg which increases the risk of egg binding, vent prolapse (part of the oviduct protrudes from the vent) , or peritonitis (infection caused by yolks falling out of the reproductive tract). All of these can lead to death through injury &/or infection.

If your hen consistently produces abnormally large double-yolk eggs, she should be watched closely for any complications that could result from stressing or injuring the reproductive tract. Some hens that produce double-yolk eggs do so with normal size eggs (we suspect these are the hereditary cases) and are at far less risk of developing any complications.

Here are multiple articles discussing double-yolk eggs, egg production, and other associated problems:


Some of the links on Mo’s Mini Farm pages are affiliate links, which means that if you decide to purchase a product through them we will receive a small commission. There is no extra cost to you! This helps us to keep the information on the website free of charge and to support our farm adventure. Because we value our integrity in recommending products, we only recommend products we have purchased and used. We may occasionally provide links to a product we are considering or planning to purchase, but we will always be sure to clearly state this fact. For more information about our affiliate relationships please see our Affiliates Disclosure Document.

Do you keep a running egg inventory?

We have multiple coops on our “mini” farm – 6 large coops and 3 smaller hutches to be exact! As part of our farm records, we began keeping a running inventory of eggs this past year. Knowing which coops are producing best can be advantageous in many ways. Good egg production indicates which layers are in best condition for performing at top levels. Most importantly, a drop in egg production can indicate many things that need to be addressed – notably illness or other problems like improper nutrition, an egg-eating problem, or even an egg-eating predator visiting your coops. When things on the farm get busy, it can be easy to not notice a drop in egg production in time to address an issue before it becomes a larger problem. Keeping an egg inventory is an easy way to prevent this. We simply created a monthly chart in MS Word, and we log how many eggs are collected from each coop every evening.

Unfortunately, collecting eggs from nine different sets of nesting boxes and remembering which came from which proved to be a daunting task. We likely had a few errors in our inventory counts. Since we are planning to focus primarily on egg production in 2018, we are hoping to establish a better method of organized egg collection. Mama Mo has searched for a basket or rigid bag with multiple compartments to be labeled for each coop, but apparently, that is not a common item for anyone. However, there may be an unusual solution to our dilemma.

Wash Boss by Bucket Boss

Mama Mo found an item called a Wash Boss – it’s an organizer that straps onto a 5-gallon bucket. The six pockets should be large enough to hold multiple eggs, and since it’s made for getting wet, cleaning should be easy. Of course, that still leaves us a few compartments short to be able to collect from all the coops, so we plan to also use another item called a Super Stacker (below) that fits inside the bucket.

Super Stacker by Bucket Boss

They are made to stack inside the bucket, but our plan is to put our custom herbal nest box mix in the bucket and put the divider on top. This way we can also refresh nest boxes as we go, if needed. Nothing beats consolidating chores!

We have all of our coops named, so it will be easy to label each compartment and know exactly which eggs came from which coops, especially when spring arrives and everyone is in full egg production mode. When we get it all put together and test it out, we’ll post about the pros and cons of our little “innovation”.