Cindy and Walt make some excellent points. And Walt your post scared the dickens out of me! A closed flock for 30 years and now you get this pop up?? Ouch!
Having said that, both Cindy and Walt's post - but especially Walt's - add a great deal of merit to why I say that one should maintain a closed flock AND linebreed while keeping meticulous records. I know of no other way to identify the culprit that is the contributing factor to a problem that rears its ugly head. If you know who each parent is and keep track of each subsequent mating, you can go back and identify where the problem is originating.
This requires a lot more time and effort but I believe it's worth it in the long run. And even linebreeding isn't the best because I've seen where breeding one male to four or five full blood sisters can result is an oddity and then the only recourse is to get rid of the entire line of females if the male is ruled out as the problem maker. Single mating or in other words 1 on 1 is probably the best but I have neither the time, space, or energy to do that.
God Bless,
I like to think that I am a serious breeder and serious breeders need to keep track of their birds and keep very good records. I toe punch all my chickens and waterfowl, so even if they lose their metal bands, I will still know who their parents are. Since our chickens have been made by crossing breeds somewhere down the line, things can pop out from time to time. This is not unusual in most flocks. I have enough birds so that I can be ruthless in culling. I can't afford to tolerate any kind of DQ popping up, so when it does I cull hard.....but I know where it came from, so I only need to cull the birds involved. If you consider the benefits, I don't think it is time consuming. I am willing to spend some time in the beginning to make the end easier. You can use one male with multiple females if you trap nest the females.
Walt