I don't think deformed animals should be bred further or sold out, they should be culled as soon as you see the deformity. Keep the gene pool clean
Imperfect animals are not necessarily caused by genetics. There are any numbers of variables that can lead to any number of imperfections, however slight.
~~McKinsey~~
"Men have forgotten this truth," said the fox. "But you must not forget it. You become responsible, forever, for what you have tamed."
~The Little Prince; Antoine de Saint Exupery