Before I talk about that, I'm going to post a picture from my childhood. It's not a personal picture, but it's a picture of what the smog was like in Los Angeles in 1968 or so:
So what does this have to do with US chickens? Well, when you buy locally produced (local in this sense means "made in the USA") meat and produce, you're getting a benefit that you may not have thought about. The places that produce that food all have to work within the US regulations regarding pollution and impact on their local communities.
From the memory of my stinging eyes I can clearly see that the regulations have made a difference, and whenever you buy something made here, in the USA, you're supporting a business that is doing the right thing, or at least better, than the alternative.
I'm a supporter of Country Of Origin labeling for this reason. Where your food comes from counts. Support the countries that do the best job with your dollars. This applies to all of your food, and even to the country where your food is processed. The factory in china doesn't have to abide by the USA pollution rules, and while it may make the shareholders a few more dollars is it really worth it?
Personally I don't think so.