Difference between oyster shell and oyster shell grit.

[ChickenCanoe]

People around here use oyster shell as grit as well. The stuff is rock hard for a long time.

And they would be wrong to do so. Oyster shell may feel hard to the touch but in the wet acidic environment of the proventriculus, it turns to mush and is quickly pulverized in the gizzard. Appropriate sized insoluble grit like granite or flint, on the other hand, lodges in the gizzard aiding in grinding food for a long time till the grinding and acidity eventually dissolve it. Oyster shell doesn't last more than a day in the digestive tract but true grit will remain in the gizzard a week or more depending on the size.
If chickens had to rely on oyster shell for grit, they would be consuming way too much calcium while trying to get something to help them grind/digest feedstuffs.

My hens are Bantams and I have read that oyster shell come in pretty big pieces and worry if the hens will be able to eat it when they want.

IMO, if an adult chicken can swallow a mouse, they can easily swallow any size bit of crushed OS.

 

[Birdsong 82]

Actually my hens Will pick around the Oystershell when I add it to their food. It should not be used as grit though because it is a softer shell and does not work the same. It feels hard but not once it hits their stomach. If you do want to give them oyster shell though there are lots of brands of feed that have it added in and it’s a lot smaller so my eat it without realizing it. Or you could grind it in a food processor. Most people don’t have any problem with their chickens eating it but I guess mine are just .... Well special. LOL

 

[ChickenCanoe]

Why would you add oyster shell to a complete feed?
Layer feed is about 4% calcium and about right for most hens in production.
Oyster shell is 98% calcium carbonate and CaCO3 is 40% elemental calcium. Even if your hens are able to eat around the chunks, just the dust would boost the calcium content of the feed to the point that you are forcing the hens to consume an unhealthy amount of calcium.

If you are feeding something other than layer feed like All Flock or Grower, you still shouldn't mix it since you don't know what the end result is in regards to total calcium percentage.

Feed manufacturers may add oyster shell to feed or they may use some other source of calcium but the feed is still assayed to guarantee the appropriate nutrient levels for the age of bird eating it and as listed on the guaranteed analysis tag.

There isn't a great deal of advantage using one source of calcium over another in feed formulation. Once passed through the hammermill and mixed, the oyster shell would be so finely ground as to have no advantage over any other Ca source.

The advantage of using crushed oyster shell free choice, in a separate container, is that the hens with high egg laying can choose to eat it when they feel the need to supplement the 4% in the feed. And the large particles spend more time in the upper digestive tract rather than that in feed and thereby makes contact with the calcium absorption sites in the small intestine at night when the egg is in the shell gland.