Why Is Supplemental Calcium Necessary for Egg Formation?

 

Most feeds that are available at your local feed store have the average amount of vitamins, minerals, protein, ect... required for chickens. However, the average amount is based on the assumption that your chickens will only eat the purchased feed, and nothing else. If that is the case, then you probably won't have any complications with thin-shelled eggs, or "ghost eggs." 

On the other hand, lets say that your chickens are eating grass, bugs, ect... or have access to table scraps. That means that their daily feed intake is not entirely from the purchased feed, but is reduced by the availability of other food options. Since purchased feed is formulated for the average amount of nutrients per chicken per day, any reduction in that intake will lead to one or many deficiencies in a flock. The most common, and most noticeable, deficiency that can arise is a calcium deficiency. 

Back before chickens were able to lay hundreds of eggs per year, they were just like most other birds, in that they laid their eggs in the spring for the purpose of hatching chicks. The hens would draw calcium from their own bones to reinforce the egg shells, but since egg production wasn't a huge "drain" on nutrients, the hens would recover and restore the calcium used to form the eggs. However, now that chickens lay eggs year round, continually drawing calcium from their bones will lead to brittle bones, which will then break; and ultimately, the hen would die from being so frail. 

Even with today's commercially formulated feeds, chickens can still become deficient in calcium, especially if allowed access to grass, ect... While the deficiency may not be as big as if there were no calcium present in the feed, the hen will still try to make up the difference by drawing calcium from her bones. Often, the hen's ability to make up the difference will only last so long before "ghost eggs" start showing up (a ghost egg is an egg without a shell, but is wrapped in the inner membrane of the egg, making it look ghost-like). While ghost eggs are still edible, the chances of getting to it before it gets broken are pretty slim:) Besides, eating eggs with a complete shell is more appetizing than one without a shell. 

How to combat calcium deficiency...

The simple answer is....feed more calcium! Sounds easy, right? Well, yes...and no. 

As you can see in the picture above, there is a 50lb bag of oyster shell. Oyster shell is taken from (you guessed it) oyster shells, which is then smashed into small bits, bagged, then shipped to feed stores. I prefer using oyster shell because of it's price per bag, compared to limestone. They both do an excellent job reinforcing egg shells, but the cheaper option works just as great as the more expensive option. Some of the smaller bags (5, 10 lb) that you can buy at D&B Supply aren't as good in my opinion, partly because the price per pound is greater than the 50lb bag, but also because the limestone/aragonite chunks are quite a bit bigger than the 50lb bags of oyster shell or limestone. The bigger the chunks, the less likely a chicken is going to voluntarily eat it, until she absolutely has to. 

How much to feed? 

The easy way is to put a separate feeder pan where the chickens can easily access it, and just fill it as needed. The chickens can "self-medicate" when it comes to calcium needs. If you prefer to have everything mixed together, I have found that an additional 1/2 lb of oyster shell per day (per 31 lbs of feed) does a pretty good job for all my 165 hens. (Note: the prepared feed that I use has 3-4% calcium present in it). Since animals are usually pretty good at "self medicating" when it comes to nutritional supplements, accidentally adding a little more oyster shell to the bird's feed won't hurt them, because they will only eat as much as necessary, leaving the rest behind. There are exceptions to what vitamins/minerals can be left out, such as selenium, which can be extremely poisonous if overfed. 

Keep in mind that the older a chicken is, the thinner her egg shell will be, which will require more calcium, but it still may not help, just because the chicken is old. I had a chicken once who just decided to lay ghost eggs for the rest of her life (not very long), regardless of how much calcium was available. She didn't stay around for much longer.

You can get oyster shell and limestone at D&B Supply for $11 and $14 per 50lb bag, or, you can probably find calcium supplements online, as with everything:)