This hen that I had to kill is the only vent prolapse that we've had. I am sure that laying eggs on the larger spectrum compared to her pinch tailed relatives did contribute to the problem. But I've got other hens that lay larger sized eggs who are not pinched in the tail, that are several years old, and have no issues - so I do think that being pinched in the tail can cause a problem if all the right conditions are met. This one was only a little over a year when I had to kill her.
That's the thing with chickens - there are so many variables and you have to get the right combination of conditions together to see a good or bad outcome sometimes.
Like NanaKat, I examine birds prior to picking the breeders - even the males are looked at, including being wide all the way from shoulder to butt, if they are going to make the cut to be a breeder bird. Yes, their breed standard calls for this, because they are dual purpose birds meant to be decent layers and decent meat birds all in one body. But when you're looking at birds for production, I think it's important to look at the things that could cause problems in the long run either in pinched tails resulting in egg binding or prolapses if the right conditions align themselves, or in not having a skeletal system that is well built to handle the strain of being a meat bird. People who have a skeletal system that is mal-aligned are going to have more problems in the long run, because the stress on their bones/joints and muscles are not going to be normal. They are going to have abnormal stress placed on their body which will cause more pain and cause further bone and muscle issues because their body is trying to compensate for the abnormality. So in a pinched tail bird, which can be inherited, that could be more stress on the bird's body which in turn may not be as comfortable for them when you are pushing them to achieve certain goals. And it could also decrease their ability to carry a good amount of meat on their frame or cause problems related to laying if they lay normal sized eggs but those eggs are too large for their body to handle.
In seeing the number of people, including my non-serious breeding chicken friends, who experience issues in their small flocks, while at any given time I've got around 100 adult chicken hens in addition to turkeys and guineas, and yet my flock's illnesses/seemingly idiopathic abnormalities are rare, tells me that there is something to be said for selective breeding and certain husbandry methods. But it takes work and it can often mean killing birds, which many people aren't willing to do. I don't think that having pinched tailed birds for the average backyard chicken keeper is the most horrible thing in the world - plenty of chickens do just fine with pinched tails. But I think for someone who is breeding seriously, even for meat production, a pinched tail is something to be concerned with because there are issues that can come up with the birds and you may not get them to reach their full potential if you ignore pinched tails completely. And when you're trying to avoid the need to constantly get new blood into your flock, there may come a time when you breed yourself into a corner if you let certain flaws, especially musculoskeletal flaws, go completely unchecked. A bird's skeleton is its foundation and you want a sturdy foundation for them to be based off of for maximum performance and bird comfort.
