One of the most important nutrients needed for eggshell formation is calcium. Most of us understand that laying hens need calcium to make eggshells and realize that commercially produced layer feed contains some calcium, but it may not be clear why providing oyster shells, a second source of calcium, is beneficial to laying hens. So let’s take a deeper look into why oyster shell is used in laying hen diets.
I had the chance to speak with Dr. Gordon Ballam and Dr. Patrick Biggs, both seasoned poultry nutritionists at Purina Animal Nutrition, about this whole calcium thing and I’ve got the Cliff Notes version of the calcium story for you!
To make eggshells, laying hens require 4-5 grams of calcium per day, which is three times more dietary calcium than non-laying hens, according to Dr. Biggs.
Eggshells are composed of 94% calcium carbonate and hens cannot make calcium, so it must be supplied in their diet. The most common sources of calcium carbonate fed to laying hens are crushed limestone and oyster shell. Commercially prepared layer feeds ordinarily contain limestone, while oyster shell is usually offered to hens by chicken keepers as a supplement to the layer feed.
If laying hens don’t get calcium when they need it, they will steal from the calcium stash inside their cortical bones to produce eggshells. This calcium theft can cause brittle bones that fracture easily and in the most severe cases, the inability to stand (aka: caged-layer fatigue).
There are two types of calcium ordinarily fed to backyard laying hens: crushed limestone, which layer feed already contains, and oyster shell, which we ordinarily offer to them in a dispenser or dish near their feeder. Crushed limestone can be thought of as a fast-release source of calcium because it’s small and is absorbed easily and quickly. Oyster shell is more of a slow-release source of calcium because it is large and sits in the gizzard, getting ground up a little at a time before being absorbed by the hen. A form of slow-release calcium is important because eggshells are formed at night when the hen is asleep, not consuming calcium-containing feed.
The time it takes for most food particles to pass through a chicken is very short – about 90 minutes, according to Dr. Biggs. Bigger particles take longer to pass through a hen, which is why providing oyster shell during the day can help to provide more calcium at night. A slow-release calcium takes much longer to breakdown, providing calcium throughout the night.
The gizzard is a muscle in a chicken’s digestive tract responsible for grinding
fibrous food with the help of grit (sand/stones/oyster shells, etc.)
WE THOUGHT SHE WAS JUST SLEEPING AT NIGHT!Of the approximately 25 hours needed to create an egg, 18-20 of them are dedicated to shell formation, which occurs overnight while a hen sleeps. A hen can use and replace the calcium it carries in its bloodstream up to 100 times overnight! #mindblown
According to Dr. Biggs, Purina Animal Nutrition recently added Oyster Strong™ System to their layer feeds; this system includes oyster shell and other minerals & vitamins needed for a strong shell in addition to the limestone it always contained. The Oyster Strong™ System eliminates the need to offer hens a separate hopper of oyster shell (except in hot weather when hens eat less feed).
Learn why hens need even more oyster shell in hot weather HERE.
When I first noticed the new Purina Layena® bag design with the “Oyster Strong™ System,” logo, I thought to myself, “I love the blue, retro vibe; these will make such adorable tote bags!” Probably not the reaction the folks at Purina were hoping for, but...that’s how it went down. Now I understand what the Oyster Strong™ System does for my hens’ health and eggshells and I love that too.
The take-home message: if you feed your flock Purina® Layena® with Oyster Strong™, it contains all the calcium they need. If you don't feed your flock Layena®, be sure to offer them large pieces of oyster shell free-choice. Eggshells offered with oyster shell are fine, but are not a sufficient source of supplemental calcium by themselves.
They do make cute tote bags too, don't they? :)