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The term “neuter” is often reserved for male sterilization in common use, but the term neuter actually refers to sterilization of either sex. The specific term in males is castration. This is a commonly performed surgery which removes the testes of the male so that they do not have any sperm and have reduced testosterone as well. This operation reduces male behaviours like roaming, fighting, mounting, and territorial marking.

The surgery is normally carried out in the young animal, usually about six months of age before puberty, but if needed the operation can be done later in life. 

The surgery is a brief procedure done with general anesthesia so that the patient is unconscious, and cannot feel anything. Pain management is carried out starting before surgery begins and continues when the pet is discharged home. Pre-op bloodwork is frequently recommended prior to the anesthesia to ensure the pet is not harbouring any hidden organ function problems or silent infections. 

The procedure is the same in principle in dogs and cats, but the surgical technique varies between them.

In dogs, after anesthesia begins, the dog is placed on the back or side, and the area which has been prepped with antibacterial solutions is draped and clamps put on the skin to hold the drapes in place. A cut is made through the skin to the depth of the fibrous coating of the testis in the skin in the midline, and the testis is exteriorized (brought out of the skin) so that a good view is obtained of the stalk which joins the testis to the internal structures. 

Two distinct approaches exist—the open and the closed technique. In the closed technique the tissue surrounding the stalk is left intact and a ligature (stitch) is tied to cut off the blood vessel and spermatic cord together inside the sheath. Then the testis is removed, and the process repeated on the other side. In an open method, the tunic layer is cut and directly exposed blood vessel and spermatic cord are tied off.

Both techniques can be used with equal success, the decision of which way to do it is surgeon’s preference. In cats, the skin cut is made over the middle of each testis, rather than on the midline in front as in dogs. In cats, sometimes the cord joining the testis to the body is tied upon itself rather than using a suture to tie it off. 

Once the testes have been removed, in dogs the tissues under the skin are closed, and sometimes a layer of stitches is placed in the skin. 

Recovery from the anesthesia and procedure is usually quick and uneventful. Frequently the biggest problem is keeping Tom or Fido quiet enough during the healing phase! Animals seem to recover very quickly from these surgeries. Sometimes a tranquilizer or head cone is necessary to keep the pet from bothering the surgery site, this is most frequently a concern in dogs.

Complications are uncommon and include infection, surgery site breakdown with extrusion of fat or rarely, herniation of abdominal contents. As well, the area has lots of blood supply so sometimes bleeding occurs under the incision area, and may ooze out or produce bruising with attendant dark swelling. 

Though not commonly done in North America, a vasectomy can also be done. This operation ties the sperm cord closed so the dog cannot reproduce, but leaves the testes in the sac so that the testosterone levels remain as for an intact male dog. This means roaming, fighting, and assertive behaviour may be more likely observed.

It is a short procedure and the dog or cat recovers quickly, and it is tough to keep them quiet post-op, but this is important to maintain low stress on the incision area.

Sometimes tomcats and dogs are born with their testes still in the abdomen or in the canal leading from the abdomen to the scrotum. Animals with both testes retained are called cryptorchid, and those with one retained are termed monorchid. The operation to remove these retained testes is more complex. If both are retained in the abdomen, an abdomen incision is made. If one is in the sac and one in the abdomen, two incisions are made. Those testes sitting in the canal may require ultrasound be used to find out where they are because especially in an obese patient, they can be hard to find. The cost of this operation will be higher than a routine procedure. It is important to remove retained testes since they are more prone to becoming cancerous. Note that those animals with retained testes should not be bred since it is an inherited trait.