I define vigor as anything in its genetic make up that predisposes a flock or individual chicken to survive and thrive as livestock. High hatchability, disease resistance, adaptations to different climates, freedom from physical defects, foraging skill, are all examples of things that help a flock survive and thrive as livestock. I have not personally hatched a single sport white Legbar, but multiple people that have and are/were trying to develop white breeding lines have reported low/zero hatch rates. Some even have made the effort to ship self white stock to other parts of the country so that they didn't have to do any close relation pairing or tried to cross the whites back to unrelated standard colored stock with out any better luck. A variety that fails to reproduce is not going to survive so it is "struggling with vigor". I hope that some people will have success in breeding the self white Legbars so that can be reversed. I know of other breeders that have developed white varieties from recessive white sports. I have never worked with any of those either, but know that they have succeeded with white varieties based on Recessive white, so I am not sure why the White Legbars are off to a rocky start, but vigor in the White Legbars is a major concern at this point.