What happens if dogs from the same litter are bred together?

Inbreeding produces puppies with possible congenital defects, increasing genetic disease, malformation, poor development, and early death. To avoid mismating within a litter, fit the female with a dog diaper during heat.

If you have no breeding plan, spay/neuter promptly; spaying cuts pyometra and mastitis risk and lengthens life, while neutering prevents prostate disease and roaming or marking behaviors.