Entire (animal)


Neutering, from the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became the ...

''neuter'' ('of neither sex'), is the removal of an animal's
reproductive organ A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction Sexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process by which new in ...
, either all of it or a considerably large part. "Neutering" is often used incorrectly to refer only to male animals, but the term actually applies to both sexes. The male-specific term is castration, while spaying is usually reserved for female animals. Colloquially, both terms are often referred to as fixing. In male horses, castrating is referred to as ''
gelding A gelding is a castrated horse The horse (''Equus ferus caballus'') is a domesticated odd-toed ungulate mammal. It belongs to the taxonomic family Equidae and is one of two Extant taxon, extant subspecies of wild horse, ''Equus ferus''. The hor ...
''. An animal that has not been neutered is sometimes referred to as ''
entire *In philately, see Cover (philately), Cover *In mathematics, see Entire function *In animal fancy and animal husbandry, entire (animal), entire indicates that an animal has not been desexed, that is, spayed or neutered *In botany, an edge (such as o ...
'' or ''intact''. Neutering is the most common method for animal sterilization.
Humane societiesHumanity is a virtue linked with basic ethics of altruism derived from the human condition. It also symbolises human love and compassion towards each other. Humanity differs from mere justice in that there is a level of altruism towards individuals ...
animal shelter Indoor dog kennels at a shelter Image:Black cat Animal Rescue GalawebDesign.jpg, A cat at an animal shelter An animal shelter or pound is a place where stray, lost, abandoned or surrendered animals – mostly dogs and cats – are housed. The wo ...
s, and
rescue group An animal rescue group or animal rescue organization is dedicated to pet adoption. These groups take unwanted, abandoned, abused, or feral, stray pets and attempt to find suitable homes for them. Many rescue groups are created by and run by Volun ...
s urge pet owners to have their pets neutered to prevent the births of unwanted
litters Litter consists of waste products that have been discarded incorrectly, without consent, at an unsuitable location. Litter can also be used as a verb; to litter means to drop and leave objects, often man-made, such as aluminum can upAluminum foo ...
, which contribute to the overpopulation of unwanted animals in the rescue system. Many countries require that all adopted cats and dogs be sterilized before going to their new homes.

Methods of sterilization

Females (spaying)

In female animals, spaying (more technically termed ovo-
hysterectomy Hysterectomy is the surgical removal of the uterus. It may also involve removal of the cervix, ovaries ( oophorectomy), Fallopian tubes ( salpingectomy), and other surrounding structures. Usually performed by a gynecologist, a hysterectomy ma ...

or ovariohysterectomy) involves abdominal surgery to remove the
ovaries The ovary is an organ found in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube The Fallopian tubes, also known as uterine tubes, salpinges (singular salpinx), or oviducts, are tubes tha ...

uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Ro ...

(in humans, this is called a hystero-
oophorectomy Oophorectomy (; from Greek , , 'egg-bearing' and , , 'a cutting out of') is the surgical Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical or dental specia ...
). Another option is to remove only the ovaries (oophorectomy or ovariectomy), which is mainly done in
cat The cat (''Felis catus'') is a domestic species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined a ...
s and young
dog The domestic dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated form of wolf. The dog descended from an ancient, extinct wolf, with the modern grey wolf being the dog's nearest living relative. The dog was the first ...

s. Another, less commonly performed method is an "ovary-sparing spay" in which the uterus is removed but one (or both) ovaries are left. Traditional spaying (removal of uterus and ovaries) is performed commonly on household pets (such as cats and dogs) as a method of birth control. It is performed less commonly on
livestock Livestock are the domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable ...
, as a method of birth control or for other reasons. In
mare A mare is an adult female Female (symbol: ♀) is the sex of an organism, or a part of an organism, that produces non-mobile ovum, ova (egg cells). Barring rare medical conditions, most female mammals, including female humans, have two X ch ...

s, these other reasons include
behavior modification Behavior modification is a treatment approach that replaces undesirable behaviors with more desirable ones by using the principles of operant conditioning. Based on methodological behaviorism, overt behavior is modified with consequences, including ...
. A complete ovariohysterectomy may involve removal of the ovaries, uterus,
oviduct The passageway from the ovaries The ovary is an organ found in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube The Fallopian tubes, also known as uterine tubes, salpinges (singular salp ...
s, and
uterine horns The uterine horns are the points where the uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around ...
. The surgery can be performed using a traditional open approach or by laparoscopic "keyhole" surgery. Open surgery is more widely available, as laparoscopic surgical equipment costs are expensive. Traditional open surgery is usually performed through a ventral midline incision below the
. The incision size varies depending upon the surgeon and the size of the animal. The uterine horns are identified and the ovaries are found by following the horns to their ends. There is a ligament that attaches the ovaries to the body wall, which may need to be broken down so the ovaries can be identified. The ovarian arteries are then ligated with resorbable
suture material
suture material
and then the arteries transected. The uterine body (which is very short in litter-bearing species) and related arteries are also tied off just in front of the
cervix The cervix or cervix uteri (Latin, 'neck of the uterus') is the lower part of the uterus in the human female reproductive system. The cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape, which changes during pregna ...
(leaving the cervix as a natural barrier). The entire uterus and ovaries are then removed. The abdomen is checked for bleeding and then closed with a three-layer closure. The linea alba and then the subcutaneous layer are closed with resorbable suture material. The skin is then stapled, sutured, or glued closed. For suturing the feline linea alba, the most appropriate suture bite and stitch interval size was suggested to be 5 mm. Laparoscopic surgery is performed using a camera and instruments placed through small incisions (ports) in the body wall. The patient is under anaesthesia and lying on the back. The incisions are between and the number varies according to the equipment and technique used. The surgeon watches on a screen during the operation. The first port is made just behind the umbilicus and the camera is inserted. The abdomen is inflated with carbon dioxide gas to create a space in which to operate. A second port is introduced a few centimeters in front of the navel and a long grasping instrument called a Babcock forceps is inserted. The surgeon finds the ovary with the instrument and uses it to suspend the ovary from a needle placed through the abdominal wall. This lifts the ovary and uterus safely away from other organs. The surgeon then removes the grasping instrument and replaces it with an instrument that cauterizes and cuts tissue. This instrument uses electricity to heat the blood vessels to seal them and to cut them. No sutures are placed inside. The ovary is separated from the uterus and round ligament. The cautery instrument is removed and replaced by the grasping instrument, which is used to pull the ovary out through the small abdominal incision (port). This is repeated on the other side and the small holes are closed with a few sutures. Another method uses ligatures and even the uterus is removed. In female dogs only removing the ovaries and not the uterus is not state of the art because this way the risk of
pyometra Pyometra or pyometritis is a uterine infection. Though it is most commonly known as a disease of the unaltered female dog, it is also a notable human disease. It is also seen in female cattle Cattle, or cows (female) and bulls (male), are th ...

persists. The benefits of laparoscopic surgery are less pain, faster recovery, and smaller wounds to heal. A study has shown that patients are 70% more active in the first three days post-surgery compared to open surgery. The reason open surgery is more painful is that larger incisions are required, and the ovary needs to be pulled out of the body, which stretches and tears tissue in the abdomen (it is not uncommon for patients to react under anaesthesia by breathing faster at this point). Spaying in female dogs removes the production of
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens, and is the major ...

, which is a natural calming
hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior. Hormones are required for t ...

and a
serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vaso ...

uplifter. Spaying may therefore escalate any observable aggressive behaviour, either to humans or other dogs. The risk of infections, bleeding, ruptures, inflammation and reactions to the drugs given to the animal as part of the procedure are all possibilities that should be considered.

Males (castration)

In male animals,
castration Castration (also known as orchiectomy or orchidectomy) is any action, surgical, chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substan ...

involves the removal of the
testes Testicle or testis (plural testes) is the male reproductive gland or gonad in all animals, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primaril ...

(testicles), and is commonly practiced on both household pets (for birth control and behaviour modification) and on livestock (for birth control, as well as to improve commercial value). Often the term ''neuter' is used to specifically mean castration, e.g. in phrases like "spay and neuter".

Surgical alternatives (vasectomy, tubal ligation, "gomerization")

Vasectomy Vasectomy is a surgical procedure for male Sterilization (medicine), sterilization or permanent contraception. During the procedure, the male vas deferens, vasa deferentia are cut and tied or sealed so as to prevent sperm from entering into the ure ...

: In a more delicate procedure than castration, the
vasa deferentia The vas deferens (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Ro ...

vasa deferentia
– ducts that run from the testes to the
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproducti ...

– are cut then tied or sealed, to prevent
sperm Sperm is the male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot sexual reproduction, reproduce sexuall ...

from entering into the
urethra The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine f ...

. Failure rates are insignificantly small.
Breeders A breeder is a person who selective breeding, selectively breeds carefully selected mating, mates, normally of the same breed to sexually reproduce offspring with specific, consistently replicable qualities and characteristics. This might be as a ...
routinely have this procedure carried out on male
ferret The ferret (''Mustela putorius furo'') is the domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group ...

s and
sheep Sheep (''Ovis aries'') are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order (biology), order Artiodactyla, the even-toed ungulates. Although the name ''sheep'' applies to many species ...

to manipulate the estrus cycles of in-contact females. It is uncommon in other animal species. Because a vasectomy is usually a more expensive procedure, among pet-keepers it is more often performed on show animals, to cosmetically preserve their appearance (though depending upon the fancier organization, the procedure may invalidate the animal's candidacy for certain awards, or relegate it to a non-
pedigree Pedigree may refer to: Breeding * Pedigree chart, a document to record ancestry, used by genealogists in study of human family lines, and in selective breeding of other animals ** Pedigree, a human genealogy (ancestry chart) ** Pedigree (animal) ...
, generic "household pet" competition division, just as with full castration).
Tubal ligation Tubal ligation (commonly known as having one's "tubes tied") is a surgical procedure for female sterilization in which the fallopian tube The Fallopian tubes, also known as uterine tubes, salpinges (singular salpinx), or oviducts, are tubes that ...
: Snipping and tying of
Fallopian tube The Fallopian tubes, also known as uterine tubes, salpinges (singular salpinx), or oviducts, are tubes that stretch from the ovaries The ovary is an organ found in the female reproductive system that produces an ovum. When released, this tra ...

Fallopian tube
s as a sterilization measure can be performed on female cats, dogs, and other species; it is essentially the female equivalent of vasectomy, but a more invasive procedure. Risk of unwanted pregnancies is insignificantly small. Only a few veterinarians perform the procedure. Like other forms of neutering, vasectomy and tubal ligation eliminate the ability to produce offspring. They differ from neutering in that they leave the animal's levels and patterns of
sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the ...
unchanged. Both sexes will retain their normal reproductive behavior, and other than birth control, none of the advantages and disadvantages listed above apply. This method is favored by some people who seek minimal infringement on the natural state of companion animals to achieve the desired reduction of unwanted births of cats and dogs. "" is breeders' informal term for surgical techniques by which male livestock, such as bulls, retain their full
libido Libido (; colloquial Colloquialism or colloquial language is the style (sociolinguistics), linguistic style used for casual communication. It is the most common functional style of speech, the idiom normally employed in conversation and other in ...
(and related effects like sex
pheromones exposes Nasonov's gland (white – at tip of abdomen) releasing pheromone to entice swarm into an empty hive A pheromone (from Ancient Greek ' "to bear" and hormone) is a secreted or excreted chemical factor that triggers a social response in mem ...
that would be lost through castration), but are rendered incapable of
copulation Sexual intercourse (or coitus or copulation) is sexual activity typically involving the insertion and thrusting of the penis A penis (plural ''penises'' or ''penes'' ) is the primary sexual organ that male Male (♂) is the sex of a ...
. This is done to stimulate and identify estrous females without the risk of transmitting
venereal diseases Sexually transmitted infections (STIs), also referred to as sexually transmitted diseases (STDs), are infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multipl ...
or causing a pregnancy by a male other than the one intended for
selective breeding This Chihuahua mix and Great Dane shows the wide range of dog breed sizes created using selective breeding. Selective breeding (also called artificial selection) is the process by which humans use animal breeding Animal breeding is a branch o ...
. Animals altered for this purpose are referred to as teasers (teaser bulls, etc.), or gomers. Several methods are used. Penile translocation surgically alters the penis to point far enough away from its normal direction that it cannot manage
vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the Vulval vestibule, vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucous membrane, ...

l penetration. Penile fixation permanently attaches the penis to the abdomen so that it cannot be lowered for penetration.
Penectomy Penectomy is penis removal through surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical or dental specialty that uses operative manual and instrumen ...
is the partial or complete removal of the
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproducti ...


Nonsurgical alternatives


* Male dogs – Two intratesticular injectable formulations are known to sterilize male dogs. Zeuterin was approved by the United States Food & Drug Administration for permanent sterilization of male dogs ages three months and older by causing necrosis of the testicle. It is not currently available commercially. Calcium chloride dissolved in a variety of diluents have also been studied, with the majority of research and most promising results using calcium chloride dissolved in ethyl alcohol. Calcium chloride formulations can be purchased for use in animals from compounding pharmacies, but the use of calcium chloride for sterilization of males is not approved by the FDA or any other international regulatory agency. *Male cats – Calcium chloride formulations have also been studied in male cats. *Male rats – Adjudin ( analogue of indazole-carboxylic acid), induces reversible germ cell loss from the seminiferous epithelium by disrupting cell adhesion function between
nurse cells Nursing is a profession within the health care sector focused on the care of individuals, families, and communities so they may attain, maintain, or recover optimal health and quality of life (healthcare), quality of life. Nurses may be differ ...
and immature sperm cells, preventing . * Male mice – injection of a solution of the JQ1 molecule to bind to a pocket of BRDT necessary for chromatin remodeling, which gives the proteins that regulate how genes act access to the genetic material * Male sheep and pigs – Wireless Microvalve. A proposed non-chemical, reversible sterilization method using a
piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical st ...

polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, repeating subunits. Due to their ...

that will deform when exposed to a specific electric field broadcast from an emitter. The valve will then open or close, preventing the passage of sperm, but not seminal fluid. Located in a section of the
vas deferens The vas deferens, or ductus deferens, is part of the male reproductive system The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the ...

vas deferens
that occurs just after the
epididymis The epididymis (; plural: epididymides or ) is a tube that connects a testicle to a vas deferens in the male reproductive system. It is present in all male reptiles, birds, and mammals. It is a single, narrow, tightly-coiled tube in adult humans, ...

, the implantation can be carried out by use of a hypodermic needle. * Female mammals – Vaccine of antigens (derived from purified
porcine zona pellucidaPorcine zona pellucida is a form of zona pellucida The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a glycoprotein Glycoproteins are protein Proteins are large biomolecules or macromolecules that are comprised ...
) encapsulated in liposomes (cholesterol and lecithin) with an adjuvant, latest US paten
(as of 2006-06-06), CA paten
(issued 1999-06-15). Product commercially known as SpayVac, a single injection causes a treated female mammal to produce antibodies that bind to on the surface of her ovum, blocking sperm from fertilizing it for periods from 22 months up to 7 years (depending on the animal). This will not prevent the animal from going into heat (ovulating) and other than birth control, none of the above-mentioned advantages or disadvantages apply.


* Male mice – reversible regulation of the KATNAL1 gene in the Sertoli cell microtubule dynamics of the testes. * Female mammals – orally administered phosphodiesterase 3 inhibitor ORG 9935 daily before and during ovulation, which blocks the resumption of meiosis resulting in ovulation of a non-fertilizable, immature oocyte without rupturing the follicle.

Early-age neutering

Early-age neutering, also known as pediatric spaying or prepubertal gonadectomy, is the removal of the ovaries or testes before the onset of
puberty Puberty is the process of physical changes through which a child Biologically, a child (plural children) is a human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opp ...

. It is used mainly in animal sheltering and rescue where puppies and kittens can be neutered before being adopted out, eliminating non-compliance with sterilization agreement, which is typically above 40%. The
American Veterinary Medical Association The American Veterinary Medical Association (AVMA), founded in 1863, is a not-for-profit association representing more than 91,000 U.S. veterinarian A veterinarian (vet), also known as a veterinary surgeon or veterinary physician, is a profes ...
American Animal Hospital Association American Animal Hospital Association (AAHA) corporate logo.jpg The American Animal Hospital Association (AAHA) is a non-profit organization for companion animal veterinary hospitals. Established in 1933, the association is the only accrediting body ...
and the
Canadian Veterinary Medical AssociationThe Canadian Veterinary Medical Association (CVMA) (french: Association canadienne des médecins vétérinaires, ACMV), founded in 1876, provides leadership on national veterinary issues, advocates for animal welfare Animal welfare is the well-bei ...
support the procedure for population control, provided that the veterinarian uses his/her best knowledge when making the decision about the age at neutering.Dog and Cat Spay/Castration
at CanadianVeterinarians.net
A task force recommends that cats are spayed–neutered prior to 5 months of age. While the age-unrelated risks and benefits cited above also apply to early-age neutering, various studies have indicated that the procedure is safe and not associated with increased mortality or serious health and behavioral problems when compared to conventional age neutering. Anesthesia recovery in young animals is usually more rapid and there are fewer complications. One study found that in female dogs there is an increasing risk of urinary incontinence the earlier the procedure is carried out; the study recommended that female dogs be spayed no earlier than 3 to 4 months of age. A later study comparing female dogs spayed between 4 and 6 months and after 6 months showed no increased risk. One study showed the incidence of hip dysplasia increased to 6.7% for dogs neutered before 5.5 months compared to 4.7% for dogs neutered after 5.5 months, although the cases associated with early age neutering seems to be of a less severe form. There was no association between age of neutering and arthritis or long-bone fractures. Another study showed no correlation between age of neutering and musculoskeletal problems. A study of large breed dogs with cranial cruciate ligament rupture associated early-age neutering with the development of an excessive tibial plateau angle. Of particular note are two recent studies from Lynette Hart's lab at UC Davis. The first study from 2013, published in a well-known interdisciplinary peer-reviewed journal demonstrated "no cases of CCL (cruciate ligament tear) diagnosed in intact males or females, but in early-neutered males and females the occurrences were 5 percent and 8 percent, respectively. Almost 10 percent of early-neutered males were diagnosed with LSA (lymphosarcoma), 3 times more than intact males. The percentage of HSA (hemangiosarcoma) cases in late-neutered females (about 8 percent) was 4 times more than intact and early-neutered females. There were no cases of MCT (mast cell tumor) in intact females, but the occurrence was nearly 6 percent in late-neutered females". The second study from 2014 highlighted significant difference in closely related breeds (retrievers), suggesting that inter-breed variability is quite high and that sweeping legal measures and surgical mandates are not the best solutions to canine welfare and health. Specifically the study states: "In Labrador Retrievers, where about 5 percent of gonadally intact males and females had one or more joint disorders, neutering at 6 months doubled the incidence of one or more joint disorders in both sexes. In male and female Golden Retrievers, with the same 5 percent rate of joint disorders in intact dogs, neutering at 6 months increased the incidence of a joint disorder to 4–5 times that of intact dogs. The incidence of one or more cancers in female Labrador Retrievers increased slightly above the 3 percent level of intact females with neutering. In contrast, in female Golden Retrievers, with the same 3 percent rate of one or more cancers in intact females, neutering at all periods through 8 years of age increased the rate of at least one of the cancers by 3–4 times. In male Golden and Labrador Retrievers neutering had relatively minor effects in increasing the occurrence of cancers." In terms of behavior in dogs, separation anxiety, aggression, escape behavior and inappropriate elimination are reduced while noise phobia and sexual behavior was increased. In males with aggression issues, earlier neutering may increase barking. In cats, feline asthma, asthma, gingivitis, and hyperactivity were decreased, while shyness was increased. In male cats, occurrence of abscesses, aggression toward veterinarians, sexual behaviors, and urine spraying was decreased, while hiding was increased.

Health and behavioral effects


Besides being a birth control method, and being convenient to many owners, castrating/spaying has the following health benefits: * Sexual dimorphism, Sexually dimorphic behaviors such as copulation, mounting and urine spraying are reduced due to the decrease in hormone levels brought about by neutering. In species other than dogs, certain forms of male aggression are also reduced. Sexual behavior in cats seems to make them especially undesirable to pet owners. * Early spaying significantly reduces the risk of development of mammary tumours in female dogs. The incidence of mammary tumours in un-spayed female dogs is 71% (of which approximately 50% will be malignant and 50% will be benign), but if a dog is spayed before its first heat cycle, the risk of developing a mammary tumour is reduced to 0.35%—a 99.5% reduction. The positive effects of spaying on reduction of later mammary tumours decreases with each heat the dog has (backing up the contention that the greatest benefit to reduce future mammary tumour development is to spay before the first heat), and there is no added benefit to spaying to reduce recurrence of a mammary tumour once it has been diagnosed. * Neutering increases life expectancy in cats: one study found castrated male cats live twice as long as intact males, while spayed female cats live 62% longer than intact females. Non-neutered cats in the U.S. are three times more likely to require treatment for an animal bite. Having a cat neutered confers health benefits, because castrated males cannot develop testicular cancer, spayed females cannot develop uterine, cervical or ovarian cancer, and both have a reduced risk of mammary cancer. * Without the ability to reproduce, a female necessarily has zero risk of pregnancy complications, such as Metrorrhagia, spotting and false pregnancy, the latter of which can occur in more than 50% of unspayed female dogs. * Pyometra, endometrial cancer, uterine cancer, ovarian cancer, and testicular cancer are prevented, as the susceptible organs are removed, though Pyometra#Stump pyometra, stump pyometra may still occur in spayed females. * Pyometra (or a pus filled womb) ('Pyo' = pus; 'metra' = uterus or womb) is a life-threatening condition that requires emergency veterinary treatment. The risk of a non-spayed bitch developing pyometra by age 10 is 25% across all breeds, but can be as high as 54% in some breeds. The treatment of choice for a closed-pyometra (where the cervix is closed and the pus cannot drain) is admission to hospital, commencement on intravenous fluids and appropriate antibiotics and, once stable enough for the anaesthetic and surgery, emergency removal of the infected pus-filled uterus. Medical management can be attempted if the animal's condition allows (for example in the case of an 'open' pyometra where the pus drains per-vaginum from the uterus via the open cervix) or dictates (where the animal is too old or otherwise unwell to withstand surgery), if the owner wishes to keep the dog entire to breed or if the owner is unable to afford the veterinary fees associated with surgery. Emergency removal of the infected uterus carries a much higher degree of risk of death than a routine 'spay' operation. The risk of death from in dogs undergoing surgical treatment for pyometra is up to 17%. Thus the risk of death in entire female dogs from a pyometra, even if given correct veterinary attention can be up to 9% by 10 years of age (17% of 54%). This risk is reduced to virtually zero if spayed.



* As with any surgical procedure, immediate complications of neutering include the usual Veterinary anesthesia, anesthetic and Veterinary surgery, surgical complications, such as bleeding, infection, and death. These risks are relatively low in routine neutering; however, they may be increased for some animals due to other pre-existing health factors. In one study the risk of anesthetic-related death (not limited to neutering procedures) was estimated at 0.05% for healthy dogs and 0.11% for healthy cats. The risks for sick animals were 1.33% for dogs and 1.40% for cats. * Spaying and castrating cats and dogs may increase the risk of obesity if nutritional intake is not reduced to reflect the lower metabolic requirements of neutered animals. In cats, a decrease in sex hormone levels seems to be associated with an increase in food intake. In dogs, the effects of neutering as a risk factor for obesity vary among breeds. * Neutered dogs of both sexes are at a twofold excess risk to develop osteosarcoma (bone cancer) as compared to intact dogs. The risk of osteosarcoma increases with increasing breed size and especially height. * Studies of cardiac tumors in dogs showed that there was a 5 times greater risk of hemangiosarcoma (cancer of blood vessel lining), one of the three most common cancers in dogs, in spayed females than intact females and a 2.4 times greater risk of hemangiosarcoma in castrated dogs as compared to intact males. * Spaying and castrating is associated with an increase in urinary tract cancers in dogs, however the risk is still less than 1%. * Neutered dogs of both sexes have a 27% to 38% increased risk of adverse reactions to vaccinations. However, the incidence of adverse reactions for neutered and intact dogs combined is only 0.32%. * Neutered dogs have also been known to develop hormone-responsive alopecia (hair loss). * A 2004 study found that neutered dogs had a higher incidence of cranial cruciate ligament (CCL) rupture, a form of anterior cruciate ligament (ACL) injury. * A study of golden retrievers found that castrated males were 3 times more likely than intact males to be diagnosed with lymphoma in animals, lymphoma and 2 times more likely to have Hip dysplasia (canine), hip dysplasia. * Castration and spaying can also increase the risk of geriatric cognitive impairment, as noted in Laura J. Sanborn's meta-analysis. * About 2% of castrated male dogs eventually develop prostate cancer, compared to less than 0.6% of intact males. The evidence is most conclusive for Bouvier des Flandres, Bouviers. * In a study of 29 intact male dogs and 47 castrated males aged 11–14, the neutered males were significantly more likely to progress from one geriatric cognitive impairment condition (out of the four conditions – disorientation in the house or outdoors, changes in social interactions with human family members, loss of house training, and changes in the sleep-wake cycle) to two or more conditions. Testosterone in intact males is thought to slow the progression of cognitive impairment, at least in dogs that already have mild impairment. * As compared to intact males, castrated cats are at an increased risk for certain problems associated with feline lower urinary tract disease. They are much more likely to suffer from feline cystitis which can escalate into a life-threatening urethral blockage. * Neutering also has been associated with an increased likelihood of urethral sphincter incontinence in male dogs. *There is evidence that spaying can increase the risk of urinary incontinence in dogs, especially when done before the age of three months. Up until 12 months of age, the risk decreases as the age at spaying increases. Urinary incontinence can affect up to one out of five spayed female dogs, and develops an average of 2.9 years after the dog has been spayed. * Spayed female dogs are at an increased risk of hypothyroidism.

Current research

Various studies of the effects neutering has overall on male and female dog aggression have been unable to arrive at a consensus. A possible reason for this according to two studies is changes to Dog aggression#Factors contributing to aggression, other factors have more of an effect than neutering. One study reported results of aggression towards familiar and strange people and other dogs reduced between 10 and 60 percent of cases, while other studies reported increases in possessive aggression and aggression towards familiar and strange people, and more studies reported there was no significant difference in aggression risk between neutered and non-neutered males. For females with existing aggression, many studies reported increases in aggressive behavior and some found increased separation anxiety behavior. A report from the American Kennel Club Canine Health Foundation reported significantly more behavioral problems in castrated dogs. The most commonly observed behavioral problem in spayed females was fearful behavior and the most common problem in males was aggression. Early age gonadectomy is associated with an increased incidence of noise phobias and .

Terminology for neutered animals

A specialized vocabulary is used in animal husbandry and animal fancy for neutered (castrated) animals:

Religious views


While there are madh'hab, differing views in Islam with regard to neutering animals, some Islamic associations have stated that when done to maintain the health and welfare of both the animals and the community, neutering is allowed on the basis of 'maslaha' (general good) or "choos[ing] the lesser of two evils".


Orthodox Judaism forbids the castration of both humans and non-human animals by Jews, except in lifesaving situations. In 2007, the Sephardi Jews, Sephardic Chief Rabbi of Israel Rabbi Shlomo Amar issued a ruling stating that it is permissible to have companion animals neutered on the basis of the Jewish mandate to prevent cruelty to animals.

See also

* Animal population control * Animal shelter * Cruelty to animals * Hysterectomy * Oophorectomy * Overpopulation in companion animals * Wildlife contraceptive *World Spay Day


External links

{{wiktionary, spaying
DVM Article on health effects of spay/neuter: Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs

Determining the optimal age for gonadectomy of dogs and cats, AVMA (pdf)

Canine Spay Photos and Description
Castration Veterinary castration Dog health Surgical removal procedures Cat health Animal welfare