how long does grit last in a crop?

That's a good question....

It probably depends on the grit and what the chicken is eating. If the grit is made from a harder rock or softer one, it would wear out faster, likewise depending on if the food eaten is harder or softer. Most people just leave it in the pen free choice for the birds, they know when they need more. Chicks tend to go crazy with it when I first give it to them, and fill up on it thinking it is food, so I start them by only allowing them to have the grit dish an hour at a time with a meal, or you could sprinkle a little grit in their food the way you would sprinkle salt and pepper on your own food. Then as they get used to using it, it can be left longer and longer until they have it full time.

Quote Areial301.

grit stays in a crop the same amount of time that food stays in a crop, about 6-8 hours.   i would imaging it stays in the gizzard somewhat longer. grit in the crop will do nothing, it is a holding area.  grit in the gizzard is where the grinding action occurs.

Next time you process a chicken gizzard, slice it open and take a look at the inside.  You may well find grit inside, and if you rinse it and massage the inside you probably will work grit out of it.

The crop stores the food a chicken gobbles down, and the real grinding of food happens inside the gizzard.  The grit gets trapped in the folds of muscle inside the gizzard, and as food (grain) works it's way into the gizzard from the crop, it is ground up into a form that the chicken's intestines can break down further and digest. 

Birds have a completely different metabolism and digestive system from mammals, and it is fascinating and important to understand how their metabolism functions, so that you can provide them with the proper nutrition, understand what makes an unsanitary coop and what to do about it, as well as being able to look at the poop you are cleaning out of the coop every day and know if your birds are healthy or not. 

In general, if the chooks have access to grit they will eat enough to keep their gizzards well equipped for grinding.  In my covered run the floor is sand over gravel, and the chooks eat out there.  I'm pretty sure that any excess sand they may eat passes harmlessly through their system.

Great question that does not have a simple answer, and I'm glad you asked!

When a chicken eats they hold their food in the crop and it works into the gizzard for grinding, so it is possible to have a mass in the crop right after they eat.  The problem comes in if they don't have enough grit to grind the food in the gizzard.  If there is not enough grit, the particles of food can become trapped in the folds of the gizzard instead of the grit, and when it spoils it causes problems.

The biggest advantage to my run is that it stays perfectly dry.  I never get a muddy stinky run, and whatever the chooks leave in the sand is dessicated completely.  I also add a small amount of Feed Grade DE to the run to help with the dessication and for dustbathing.  That helps ensure that their feathers remain dry, and dry feathers are what keep a chook warm.

I compacted the gravel bed pretty tightly, then laid in 1/2 of a yard of sand, packed and watered it down, then added another half yard on top of that, and packed it too.  I have since added 3 more bags of tubesand because of continued settling.  The girls scratch up an occasional rock, but they have yet to dig that deeply.  They scratch out a shallow bowl in the sand then grovel in it.  So far it has worked just great, and the chooks have been out there since February.

: how long does grit last in a crop?so when you're holding your chicken shortly after she's eaten and you feel a full "ball" of food right at the chest (or under the neck).....is that the crop your feeling or the gizzard
The ball is a full crop, the gizzard is where the food is digested and where grit is needed, I have  butchered chickens that have gravel in thier gizzard that is the size of a pea and my chickens get all the grit they need from the ground of course I live in the ozarks where the soil is rocky if you live in a area where the soil has few rocks you would need grit in some form.