What is spay or neuter?
To start with, "spay" is for the female dog and "neuter" is for the male dog. This pretains to the removal of the reproductive orgams of the animal's body, either all of it or a large portion. The term can also be refered to as "fixing" an animal. Spaying or neutering your dog helps reduce the overpopulation of animals which is a huge issue, especially in the United States.
Most shelters or rescues require this to be done in order to "adopt" an animal.
At what age should my dog be spayed/neutered?
You may find that each country is different when it comes to this. It will also depend on if the dog is a pet, show dog, used for breeding, or is a special work dog with a physical job.
For your pet, in the United States, most shelters spay/neuter puppies as early as 6-14 weeks old. This is done at such an early age in order to control overpopulation. Other than that, most pups are spayed/neutered between 5-8 months old. Dogs should be spayed, other than the work dog/breeding exceptions, before they go into their first heat cycle.
