Pet sterilization has its supporters and opponents, but most experts agree that the average companion dog should be spayed (female) or neutered (male). "Neuter" is a common term for castration in a dog.

There are three main reasons why to Neuter/Spay your dog

1. To prevent unwanted reproduction (that means no accidental pregnancies), and in this way combating pet overpopulation (millions of unwanted dogs have difficulty in finding new proper homes).
2. To prevent the occurrence of life-threatening health conditions associated with the reproductive system, including cancer and testicular diseases.
3. To reduce possibility of developing behavioral issues that are related to gender-specific hormones (marking, aggression) - if dogs are spayed or neutered by six months of age.
   

Dog sterilization is  a routine procedure and complications are very uncommon.

When should a dog definitely be neutered/spayed

• Dog has behavioral issues or health problems.

• Dog is mixed-breed.
• Spay/Neuter is required by law.

It is acceptable not to spay or neuter a dog if the dog is purebred and healthy and shall be used for professional breeding or if a dog is in so poor health condition that spaying or neutering can risk dog's health.

Some still believe that neutering/spaying their dog will cause that the dog will become fat and lazy and that his personality will change. Some of the opponents of spaying/neutering justify their decision not to sterilize their pet on the statement that animals have right to sex and that they want to see the miracle of birth.  However, these are not arguments but rather myths about negative effects of spaying and neutering.

As the owner of your dog, you have the right to decide whether or not to have your dog sterilized. However, responsible dog owners will choose the option that is best for the dog, the community, and the overall pet population. If you decide not to have your dog sterilized, remember that unsterilized animals require extra supervision to prevent escape attempts and unplanned pregnancies.

Related Articles and Sources:
Spay or neuter surgery: Myths, facts, and drawbacks on Canismajor.com
Risks and Benefits Associated with Spay / Neuter