They would only allow breeding from dogs in good health and in a reasonable age range for producing healthy offspring. (okcpetsmagazine.com)
So if the female animal's body is too much weakened by damage, there is a real threat to her chances of making healthy offspring. (scientificamerican.com)
Having a large selection in these genes improves the immune system and can make for healthier offspring in the long run. (livescience.com)