Shelter Health

Spay/Neuter Glossary of Terms

Sterilization surgeries have been performed on animals for over a thousand years. In fact, according to the veterinary historian Smithcors, surgical procedures to sterilize male animals date back as far as 284 BC.

This article provides background information about the state of spay/neuter surgery today as well as a Glossary of Terms that defines the relevant terms of companion animal sterilization.

We are providing this information so that shelter and community leaders can have a better understanding of what is involved when discussing spay/neuter programs with veterinarians and other staff.

Spay/Neuter of Companion Animals
Common, But Not Simple Surgeries
Glossary of Terms

Spay/Neuter of Companion Animals

Sterilization procedures have been performed on companion animals for over 100 years. Today, these procedures are typically known as spay and neuter surgeries. In some countries sterilization surgeries are performed on companion animals for therapeutic reasons only. In the United States, spay/neuter procedures are an important component of any comprehensive community pet population plan to reduce the intake of unwanted animals into shelters. Spay/neuter surgeries ultimately decrease the euthanasia rate and increase the live release rate of animals. There are also medical benefits of sterilization surgery for the individual animal.

Spay and neuter surgeries are performed routinely in private veterinary hospitals, veterinary teaching hospitals, animal shelters, and high-quality high-volume spay/neuter clinics. They are considered the practice of veterinary medicine and cannot be performed by anyone other than a veterinarian. They may be performed in a stationary facility, mobile van or “MASH” style program.

While each state regulates the practice of veterinary medicine through a state board, the board does not tell veterinarians how to actually perform the procedure, A state board generally becomes involved only if conditions are substandard or there are complaints about the end result.

The quality of the surgery should never be judged on the length of the incision. The length of the incision is up to the surgeon’s discretion, and high quality sterilization surgeries can be performed through both short and long incisions. In fact, when a complication arises, a surgeon must extend the length of the incision. Incisions heal from side to side, not from end to end.

Common But Not Simple Surgeries

Veterinarians may argue about whether these procedures can be described as routine, but they will agree that they can be anything but simple. Although experienced surgeons perform hundreds of these procedures without problems, the serious nature of every surgery must not be forgotten.

A spay, which refers to sterilization of a female dog or cat (also known as ovariohysterectomy, see below) is major abdominal surgery that can be technically challenging for the surgeon, especially if the animal is obese, in heat, pregnant, has a pyometra or other hidden medical problems. Care should be taken of all patients to ensure the safety of the patient from the preoperative period through the surgical period to the post operative period.

A neuter refers to sterilization of a male dog or cat (although the term neuter technically means the sterilization of either a male or a female animal, today it is typically used to refer to the castration of a male animal, see below). A castration is a less invasive procedure than a spay, but can also be technically challenging for the surgeon if the testicles are not descended into the scrotum (see monorchid or cryptorchidism below). As with any surgical procedure, there are potential complications from both spays and neuters.

Glossary of Terms

This term refers to the surgical procedures that render an animal unable to reproduce naturally. 

This term refers to the complete removal of the testicles in a male rendering them sterile. Castration can be chemical or surgical.

This term refers to testicles that are not in the normal location in the scrotum. Cryptorchidism can be unilateral or bilateral:

  • A unilateral cryptorchid animal is a male animal that only has one testicle descended into the scrotum. (The other testicle may be in the abdomen, in the inguinal region, or in the pre-scrotal region).
  • A bilateral cryptorchid animal is one in which both testicles are retained, and therefore neither testicle is in the scrotum.

Monorchidism refers to a male animal who has only one testicle which may or may not be in the scrotum. Sterilization surgery for cryptorchid males is more complicated than standard castrations.

This term refers to the stage of the reproductive cycle when the animal is receptive to breeding. The term “in heat” is commonly used for dogs and cats in estrus. Dogs in estrus will usually display an enlarged vulva and bloody vaginal discharge, while cats in estrus will usually display only behavioral signs, such as loud and frequent vocalization, holding their tails erect, and wanting excessive petting at this time.

See alter. They are generally used interchangeably.

This generic term refers to the removal of the sex organs, which are also referred to as gonads, so it applies to both males (removal of testicles) and females (removal of ovaries).

Gravid Uterus
This term refers to a pregnant dog or cat uterus. Animals can safely be spayed during pregnancy, but the surgery performed during late pregnancy is more complicated than a standard spay, and requires surgical skill and supportive medical care as well (for example, the dog or cat should receive fluid therapy if sterilized during pregnancy).

High Quality High Volume Spay/neuter
HQHVSN programs are efficient surgical initiatives that meet or exceed current veterinary medical standards of care in providing accessible, targeted sterilization of large numbers of dogs and cats in order to reduce their overpopulation and subsequent euthanasia.

Monorchidism refers to a male animal who only has one testicle which may or may not be in the scrotum.

This term is commonly used to refer to the surgical alteration of a male to prevent reproduction, or castration, but technically it refers to the surgical alteration of either males or females to render the animal "neutered" or genderless.

This term refers to the procedure that is the same as castration, or removal of the testicles.

Ovarian remnant
When ovarian tissue is left in the body, this is called an ovarian remnant. This can not only lead to a pyometra (see below), but to the animal showing behavioral signs of heat in the future.

This term refers to the surgical removal of the ovaries only (and not the uterus) in a female so she cannot reproduce. This eliminates the production of estrogen and progesterone. This procedure is commonly done in Europe, but in the US, ovariohysterectomy is more commonly done.

(Author’s note: If a surgeon chooses to perform an ovariectomy instead of an ovariohysterectomy, although it will render the female sterile, it should technically not be referred to as a spay in order to avoid confusion with the common usage of the term. Complete removal of the ovaries but not the uterus in a juvenile animal should eliminate concerns about a pyometra developing in the remaining uterus, but this could be a problem in an animal that has had several heats before undergoing the procedure.)

This term refers to the surgical removal of the ovaries AND uterus in a female so she cannot reproduce. This procedure eliminates the production of the female hormones estrogen and progesterone. The removal of the ovaries alone would also render the animal incapable of natural reproduction, but both organs are most commonly removed in the United States.

Pediatric Spay/Neuter
Pediatric Spay/Neuter is endorsed by the AVMA and has been shown to be safe and effective. There are several terms being used synonymously for pediatric spay/neuter. It generally refers to any gonadectomy performed before the animal is 6 months of age, which was considered the traditional age. The minimum age for performing the procedure is generally considered to be 6 weeks. Some alternative terms for pediatric spay/neuter include:

  • Early Age Spay/neuter
  • Juvenile Spay/neuter
  • Prepuberal Spay/neuter
  • Prepubertal Spay/neuter
  • Prepubescent Spay/neuter

This term refers to an infection of the uterus in a female dog or cat. This bacterial infection can be severe and life threatening, and even mild pyometra cases must receive medical/surgical attention as soon as possible. A pyometra can develop secondary to the incomplete removal of all the ovarian tissue at the time of the spay.

A pyometra is considered a surgical emergency, and the sooner the infected uterus is removed the better the prognosis for the animal. Aggressive peri-operative care must be given to the patient with a pyometra, including antibiotics and fluid therapy. The spay of a patient with a pyometra is more complicated than a standard spay, and requires surgical expertise.

Scrotal Ablation
This term refers to the complete removal of the scrotum. In a standard neuter or castration, the testicles are removed from the scrotum and the scrotum remains intact. However, certain circumstances require the surgeon to remove the scrotum at the time of castration. This is a more complicated surgery, and requires surgical skill as well as cautery of the many vessels found in the scrotum.

Cases where a scrotal ablation may be necessary include any dog or cat with an injury to the scrotum or scrotal skin (such as a chemical burn in a shelter when a dog sits in a concrete run that was disinfected but not completely rinsed down), scrotal neoplasia or cancer (this is rare), or large older dogs with pendulous scrotum.

In the United States this term refers to an ovariohysterectomy, or complete removal of the ovaries and uterus in a female. A spay can be a “standard spay” which refers to the spay of a healthy young adult animal, or a spay can be a “complex spay” which refers to the more complicated sterilization of an pregnant animal, an animal in heat, an older animal, or an animal with a uterine disease such as a pyometra, etc.

Lila Miller, DVM, is Vice President of ASPCA Veterinary Outreach.

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