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Each situation is different and I'm not passing judgement on this case, but when we decide to keep livestock, we accept the responsibility to do the right thing as good animal husbandrymen. It is a difficult thing to do. I once hatched a chick with 3 legs. It appeared robust but couldn't walk and never would have so I put it down.
A lot more human infants would die without millions of dollars of medical equipment and lots of expertly trained staff in neo natal wards.
Survival of the fittest makes for vigorous generations to follow.
Frederick Painter Jeffrey, professor of poultry science at both Rutgers University and University of Massachusetts, Dean of the Stockbridge School of Agriculture, author of many poultry books including 'Chicken Diseases' advocated the "rigid culling of all snifflers, droopers, feather rufflers, poor eaters and pale-headed birds to be sure they don't reproduce their kind.
Keeping birds with genetic defects will reproduce birds with genetic defects.