Why do dogs testical come out?

This happens quite often where one or both testicles do not descend. Normally your dog does have both testicles but one is retained up inside of the abdomen. It can be genetic so do not breed a dog that this happens to. Do neuter your dog as soon as your Veterinarian says it is ok to do so. It is important as the testicle that is still retained up inside of the abdomen will most likely become cancerous in time. Please have your Veterinarian check your dog over first for his opinion.