Monthly Archives: July 2012

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…..talk 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)…..it 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…..it 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

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