Bones, Shells and Hen Health

People keep backyard hens for any number of reasons…..for companionship, for comic relief, to fertilize the garden, eat bugs, teach kids about the circle of life or to eat table scraps.  But the main reason that most people have hens around is because they do all these things AND produce eggs.  Eggs are the lynch-pin that makes henning so popular.  You (and your kids) can see how the food the hen eats today becomes your breakfast tomorrow.  It is fascinating and awe inspiring….old broccoli into an omelette… a bout a silk purse from a sows ear!

There is an aspect to egg production that puts the health of your hens at risk, however.  Each egg is presented to you in its own handy carrying case….the shell.  An egg-shell is made up of calcium carbonate.  It contains the entire

Hens in lay have “trabecular bone” that allows for the rapid storage and release of calcium when the hen is in lay. If the trabecular bone is depleted, the cortical bone (part that gives strength) will start to be used, resulting in weakness and pain for the hen.

amount of calcium the chicken can carry in her bloodstream.  This means that if a hen doesn’t eat any calcium, she will deplete her calcium stores very, very quickly.

A chicken’s bones are made of calcium phosphate.  In the currency of egg production, consider this the “bank”.  Hens eat feed that contains calcium….it’s her “income”….she deposits egg-shell….this is her “expenses”.  The bones act as a storage site (important, since she eats during the day, and deposits egg shell overnight).  Simple, right?

Sorta.   Getting enough calcium into a hen every day is tricky….the ration needs to be balanced for both calcium and phosphorus, and hens do NOT like eating a ration that contains more than 4% calcium (the amount needed if a hen is to lay an egg each day)… is very salty, and hens will back off feed when the calcium level is high in the diet, until they get used to it.  Giving oyster shell as a free-choice supplement is not enough if you have a modern laying hen breed.  Hens eat oyster shells, and they stay in the gizzard as the acid there dissolves them

The black stuff inside the gizzard is limestone…another source of calcium. It stays in the gizzard until it shrinks to less than 3mm in size, then it goes through the gut. This gizzard is quite full, but the large particles won’t provide enough calcium for the hen, if they are the sole source.

slowly….thus it is a constant drip of calcium for the hen.  Helpful, but if it is the only source of calcium, the physical limits of the gizzard, and the slow release of the calcium means the hen won’t get enough.

To further complicate things, the bones are made of calcium phosphate….therefore phosphorus is also very important for bone health (and indirectly, shell quality).  The problem is, the phosphorus level needs to be in the proper ratio with the calcium…..too much phosphorus is dangerous to the hen, and she must get rid of it through her kidneys, and will (strangely) result in the same condition as insufficient phosphorus.  In a backyard, feeding minerals becomes more art than science.  Feed sunflower seeds, edamame, flax seeds and oat bran (foods high in phosphorus), but not TOO much…..and there is no target amount to feed… depends on the amount of calcium the hens consume…..the ratio of calcium to phosphorus is the important number.

To further complicate things, if you have a modern type laying hen, her physiology is set to lay an egg a day (pretty much).  She will do this, regardless of the state of her bones, or the balance of her calcium intake vs output.  The result is poorly shelled eggs, weak bones, egg bound hens or chickens that are too weak to survive well.  Heritage breeds are not as physiologically driven to lay eggs, and will just stop laying if the mineral balance is poor.

The answer is to feed hens a ration that is balanced with a lot of calcium in it, and appropriate amounts of phosphorus added.  Feed treats and scratch as just that….treats and amusement.  Don’t try to balance your hens rations piecemeal….it is all but impossible, and the hens will suffer.  Another way to approach the problem is to use heritage breeds, which will go out of lay  much more easily, and spare themselves the effects of calcium depletion.  You will get fewer eggs, but also less problems.

Mike the Chicken Vet

14 responses to “Bones, Shells and Hen Health

  1. Can you feed ground up egg shells back to them as a source of calcium? Just curious.

    • Hi Mike;

      Yes, you can feed eggshells to hens…..the important thing is to be sure they are clean (feed mills will steam them to kill any bacteria ), and the risk is giving the hens a taste for the shells…..they might begin to try to find their own calcium treats in a neighbour’s nest.


  2. Thanks for the informative post. Can you give a rough idea of the ratio of calcium to phosphorus please?

    • Hi Julie;

      Although the ratio changes slightly as hens age, a 10:1 ratio of calcium to AVAILABLE phosphorus is a good rule of thumb. Don’t confuse crude phosphorus with available, though.


  3. Hey Mike,

    I have been dealing with two very interesting Chinese silkie chickens. I would love your opinion and have youtube videos. Do you have an email I can contact you on?


    • Hi Rayya;

      The best thing is always to get a sick animal evaluated by a vet. Even when a client calls with what sounds like a common ailment, I always try to see the birds before making a stab at treatment. You can also do a fecal float on a fresh dropping….it should show up similar to any cocci oocyst that you would find from a dog or cat.


  4. I have new baby chicks and one is screaming in pain and scratching its head a lot, not sure what is wrong with it, any ideas?

    • Hi Sandy;

      Chicks don’t usually vocalize with pain. They are very stoic animals, and the last thing prey animals want to do in the wild is call attention to themselves if they are injured or debilitated in any way. It is possible that the chick is distressed by its environment or missing something that is making him nervous. If it is an incessant “cheep-cheep-cheep” call, check to make sure that the temperature is good, and that he has the ability to see his flock-mates. As for the scratching his head, that could be itchiness, or possibly an infection. Nursing care is likely the best thing you can do for him….keep him warm, have food and water nearby, and keep him within sight of his flockmates.

      Good luck with him


  5. Hi Mike, A friend of ours Derek ( vet and a sailor friend) gave us your name when we first had chickens. A long time ago (2 yrs) we sent you pics of our chickens… lost feathers and bare… they have never regained their feathers. At the time you said they were “stressed” and we followed your instructions… (dark, rest times etc., fewer pellets, more cracked corn etc. ) We can’t let them run free or the foxes eat them. Each batch of chickens ends up the same… we feed them pellets for layers, (about 3/4 of their food) and cracked corn (for the rest of it) plus the veg from the garden, apples, and have expanded their outdoor area to about 10′ x 50′(odd shape but that’s about it)… put hay in, … I think it is the pellets (17%) that we are feeding layers… but there are 21 chickens and their egg production is about a dozen per day… Can you help? They look dreadful… all bare and pink. their wattles and combs are full and red and look healthy… just low on feathers

    • Hi Lynn;

      I’m sorry to hear that your hens haven’t recovered from the feather loss. The bad news is that the most likely cause is one or more of your hens has developed the habit of feather pulling. If you watch the flock carefully, you will likely be able to catch the culprit(s) in the act. I know of no reliable way to stop this behaviour once it is established….it usually starts from some kind of stress which translates in to aggression, which then becomes a learned behaviour that is difficult to break. Depending on the flock, you might be able to separate 1 or 2 of the aggressive hens and have the rest recover their feathers, but there is also the possibility that all the hens have learned to use this tactic to “get ahead”, and it may be a permanent condition with this flock. If you do introduce new hens, keep them away from this group unless you are sure you have the feather pickers removed from the group.


  6. Hi Mike
    I got your contact from
    Thanks for the blog, its very informative. I’m a rookie at this and have about four chicken. One of them recently started laying eggs and lost a lot of feather and after that started limping on one leg. Now she doesnt even bring the leg down and eggs arent regular as well. I was told to feed her layers mash and have just started doing that. Also started feeding them crushed egg shell mixed in the feed. Is there anything else I could do??


    • Hi Mohammed;

      I would also suggest giving some Vitamin D in the water. It can be bought at the drugstore for infants. Vitamin D helps improve calcium absorption, and it sounds like your hen has become very calcium deficient, and can use all the help she can get.


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