One of the best threads I've ever seen about impacted crops and backed up crops is this one: http://www.backyardchickens.com/t/242356/urgent-crop-problems/10 page 2, Posey's post that includes information from Prissy.
One thing I'd like to suggest, coming in so late and I haven't been able to read everything yet - forgive me for that - is figuring out the cause of the problem and then I'd suggest handling the problem itself as Posey/Prissy say to.
But the big thing is finding out the cause. Common causes are:
Grains or other non-crumbles/non-pellets given with the assumption that birds have enough grit on their own.
Suddenly feeding lots of greens.
A slowed digestive tract caused by some other issue (worms, stress, bacteria, dehydration, etc).
A sick digestive tract primarily (infection, etc)
A sick digestive tract secondarily (bird is sick with respiratory illnesses or has been medicated - a sure way to slow down digestive tracts)
Impaction with foreign object.
This is the best time to review your system:
Are your birds properly wormed. Do NOT depend on your eyes - if you see worms ever, they are severely infested. Worms do not come out - they stay inside while alive. Visable worms are those that couldn't compete with the legions of other worms that are in the digestive tract, or those that are stunned by wormers, etc. Worm twice a year minimum. By the way "wormers" are true anti-worm products like a chemical wormer. Worm-prevention aids are DE, pumpkin seeds, garlic.
Are you giving grit - no matter if your birds are inside or outside? Always provide an appropriate grit for the size of the bird. Chick grit for chicks. Chicken or pigeon grit or mineral grit for adults. The rocks you see might not be the hardness needed (granite) for breaking down food. Granite grit is ideal. Oyster shell is not grit. Backed up gizzards back up the crop.
Did you suddenly feed greens? Again - see grit.
Are your birds of good weight (meaning how they feel not on the scale - learn to understand a healthy breast bone's meat coverate - not too fat, not too thin - NOT like a store bought chicken). If they aren't, there might be worms or reduced immune system issues.
Did you suddenly change feeds? Always change feeds over a 10 day period - slowly. It takes weeks for the digest tract to adult to a new diet.
Are your birds sniffling? Draining digestive tracts change the pH of the gut, causing the system to work less efficiently.
Do your birds have parasites? Weak birds' crops won't empty.
Is there a foreign body? This is difficult to tell - but it happens. Sometimes this is when emptying the crop helps. You can sometimes feel objects through the crop wall.
Is there any indication that illness came before crop statis (a slow crop)? Anything that causes problems for the bird will cause the digestive tract to slow down.
These are some things to consider. If any of this is unclear, my inbox is backed up here, but I'd be glad to clarify. Just email me at firstname.lastname@example.org so I can come back here and clarify for everyone, please. :)
Nathalie (Ross) Norris
(p.s. Please do not reproduce any of my above ramblings without my expressed, written permission - thank you. Please feel free to link this post however - so that people can read this post in context of the whole conversation and know its origin )