Interested in theories regarding how to go about this. Since they all came from very few birds, just crossing different breeder's birds wouldn't seem to do it. We had good luck with vigor in our first line birds, but others clearly have had other experiences and some serious issues. Darwinism? If only the strong survive and we continue to breed the very small gene pool of only the strongest individuals, is that enough? Is there a viable amount of genetic material to breed forward without carefully selected new blood importation?With conscientious breeding, I think we can restore vitality to the 1st line.