The term "grit" covers a lot of ground.
It can mean 'crop stones', the pebbles the bird uses to grind food in its crop, or gizzard. These stones are not metabilised by the bird, but rather remain in the crop.
Grit also applies to oyster shell, which is a source of calcium and which the hen DOES absorb for the calcium so dear to the manufacture of strong eggshells.
I don't know about Layena, but all the layer feed I'm familiar with has the needed grit element included.
Here's the Purina promo copy for Layena:
Purina Mills
Layena SunFresh Recipe
Once your laying birds reach 18 weeks of age, they will need Purina Mills Layena SunFresh Recipe to support egg laying. Natural and wholesome like the Start & Grow products, Layena contains high calcium levels to support strong eggshell formation while maintaining a healthy skeleton. In addition, Layena is fortified with manganese to enhance shell quality. High levels of xanthophyll from marigolds result in rich, yellow yolks, while the enhanced concentration of vitamin E provides for more robust immune protection. Purina Mills Layena SunFresh Recipe contains all the quality nutrients laying hens need to produce lots of strong-shelled, healthy, golden-yolked eggs.
Sounds pretty good!
The complete breakdown is found here:
http://www.poultrynutrition.com/OURPRODUCTS/Products/Layena/default.aspx
Grit itself is sort of a minor worry, really. For hens, oyster shell grit offers calcium for egg shells. Its not really there for grinding food in the crop, if that is your worry. With the Layena, it seems the eggs shell calcium need is covered in the feed.
As for crop stone, if your birds have access to the out doors at all, they will get the grinding grit they need on their own. If not, I suspect they will do fine on the Layena alone.
I wonder how the commercial egg folks handle this issue. Im sure the feed they use is eminently digestible without needing much crop grinding. But, what do they when it comes to egg shells? Even battery egg layers have to make a shell on their eggs. Do they feed oyster shell grit or a substitute separately, or as an in-feed component?