Sponsored Post Safe eggs start with strong shells


Staff member
Premium member
8 Years
Jun 28, 2011
Tipperary, Ireland
For backyard chicken raisers, shell thickness helps keep bacteria out.


Sunny side up, over easy or hard boiled? Think about the last time you made eggs. Did the shell break in a crisp, perfect line or was the crack more of a crumble and shatter? If it was the first, your eggshells are strong and protective. If it was the second, your backyard hens could use a calcium boost.

Patrick Biggs, Ph.D., a flock nutritionist for Purina Animal Nutrition says strong shells are an important part of egg safety.

“When we raise backyard chickens, we are ultimately producing a consumable food product: farm fresh eggs,” he says. “As flock raisers, it’s our responsibility to produce eggs as safely as we can. One way to help keep eggs safe is by feeding hens for shell strength. Strong shells help keep bacteria out and eggs protected.”

Strong shells keep bacteria out

Shell strength is determined by two primary factors: thickness and pore size.

Let’s start by looking at the shell under a microscope. A strong eggshell is about 0.3 millimeters thick and has between 7,000 and 17,000 tiny pores[1]. These pores work to allow oxygen, carbon dioxide and moisture to pass through, but to keep bacteria out.

“Eggshells with larger pores or thinner shells have less protective power,” Biggs says. “A strong shell can help deflect bad bacteria, while bacteria can fit through the larger pores of a weak shell.”

The shell is then covered by a thin coating called the bloom, or cuticle, for added protection. Just inside the shell, the inner and outer membranes provide yet another layer of defense.

“These protective shields work together to keep the contents of an egg safe and healthy,” explains Biggs. “However, none of these barriers are effective unless you start with a strong eggshell; it’s the egg’s first line of defense.”

How to get strong eggshells

Realizing the importance of shell strength, many researchers have considered the connection between chicken layer feed and shell formation. The major player in the equation is calcium. Once laid, an eggshell includes 2 grams of calcium. To get this level and still maintain strong bones, a hen requires 4 grams of calcium – all of which must come from her layer feed.

The team at the Purina Animal Nutrition Center recently looked at two different calcium variables during on-farm trials: 1. Calcium in conjunction with other minerals; and 2. How quickly a chicken digests calcium.

The first finding showed that adding trace minerals, such as manganese, into layer feed can contribute to more than double the shell strength of diets without trace minerals.[2]

Next, the team looked at calcium digestion and slow-release versus fast-release calcium. It takes 20 hours for a hen to make an eggshell, with calcium needed the entire time. Therefore, both forms of calcium are required. Providing only a fast-release calcium source, like eggshells or foraged foods, can leave a calcium deficiency when a hen is sleeping.

“Layer feeds that include Oyster Strong® System take both learnings into account,” says Biggs. “The added calcium in Purina® Layena® and Purina® Layena® Plus Omega-3 have larger particle size to release calcium slowly and added trace minerals for extra shell strength. This provides essential calcium during the entire 20-hour egg formation process so you can collect safe, strong-shelled eggs each morning.”

To try a layer feed containing Oyster Strong® System and learn more about strong shells, sign-up for Purina’s new Feed Greatness™ Challenge at www.oysterstrong.com. To learn more about raising backyard chickens, go to www.purinamills.com/chicken-feed or connect with Purina Poultry on Facebook or Pinterest.

[1] “How thick is an eggshell? “University of California-Santa Barbara. http://www.eggnutritioncenter.org/blog/fun-fact-friday-an-egg-has-7000-17000-tiny-pores-on-its-shell/. 11 September 2017.

2 Purina Experiment – L84-PF44, 1984


Premium member
Mar 19, 2016
35.111165 -81.226586
My Coop
My Coop
Nice to know, despite the bit of sales propaganda. It is not an absolute necessity to have layer feed with calcium, calcium can easily be obtained from a supplementary source like ground oyster shell, perhaps with ground egg shell added in (giving them back their egg shells alone does not provide enough).

I know this for a fact because I'm giving my birds flock raiser which has no added calcium (less than 3%), and ground oyster + egg shell on the side and their egg's shells are easily thick enough. Besides, wild birds (including jungle fowl, the wild origin of the domestic chicken) have been doing just fine for thousands of years before we came along with our specially formulated feeds.

Lady of McCamley

8 Years
Mar 19, 2011
NW Oregon
I actually do see better egg quality when I use high quality layer feed rather than flock raiser and oyster shell or calcite grit.

I know many do that with good results, but I can tell the difference in shell appearance and quality.

I still provide free feed calcite grit or oyster shell, but I make a point to use the layer feed. I am happier with it.

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