I found scads of people on blogs and websites with backyard hens telling various ways to prevent it...among them was to mow the lawn short in the spring so that chickens wouldn't eat long blades of grass!
Chickens have been eating grass since the beginning of time without the benefit of a lawnmower grooming the grass beforehand, so I'm thinking this is most definitely not a cause.
About all the websites and blogs cited the long grass blades as being the primary culprit to impacted and then soured crops. They also said giving ACV would make it worse~I'm thinking it wouldn't make it "worse" per se, but it could really irritate and cause pain to the cankers in the crop, esophagus and mouth of these birds.
Now..let's see what the avian specialists say about impacted and sour crops and the root cause...it may just surprise a few people on this forum, but it didn't surprise me in the least bit. As a nurse I see this all the time:
Once again...another wonderful reason why I don't give my flock meds of any kind and particularly antibiotics. Not only is it only crutching up a weak immune system, but antibiotics shouldn't be sold over the counter to nervous lay people who have no idea of their actions in the body. Imagine if those same levels of antibiotics were sold over the counter for humans and any parent who didn't really know what their kids had could buy them and treat their own children for any little sniffle they imagined was a potential pneumonia. Disaster.
Think they have worms....give them meds. Heard a sneeze? Give them meds. Think they have coccidiosis? Give them another med. Sour crop? By all means, don't give them grass and vinegar, it could only make it worse.
My prevention techniques all these years? Grass...and vinegar. Not freshly mowed grass...lush, long, spring grass that is so tender that the tips come off in small pieces when they take a bite.
There you have it..that's all I could find of any valid information on the malady.