View source for Neutering

{{short description|Removal of an animal's reproductive organ}}
{{Use dmy dates|date=August 2019}}
'''Neutering''', from the [[Latin]] {{lang|la|neuter}} ('of neither sex'),<ref>{{cite web|url=http://www.archives.nd.edu/cgi-bin/lookup.pl?stem=neuter&ending=|title=Latin Word Lookup|website=www.archives.nd.edu}}</ref> is the removal of a non-human animal's [[sex organ|reproductive organ]], either all of it or a considerably large part. The male-specific term is '''castration''', while '''spaying''' is usually reserved for female animals. Colloquially, both terms are often referred to as '''fixing'''.<ref>[http://www.merriam-webster.com/dictionary/fix "Fix"] {{webarchive|url=https://web.archive.org/web/20140121130630/http://www.merriam-webster.com/dictionary/fix |date=21 January 2014 }} at Merriam-Webster.com</ref> In male horses, castrating is referred to as [[gelding]]. An animal that has not been neutered is sometimes referred to as '''entire''' or '''intact'''. Often the term ''neuter[ing]'' is used to specifically mean castration, e.g. in phrases like "spay and neuter".

Neutering is the most common method for animal [[Sterilization (medicine)|sterilization]]. [[humane society|Humane societies]], [[animal shelter]]s, and [[rescue group]]s urge pet owners to have their pets neutered to prevent the births of unwanted [[Litter (zoology)|litters]], which contribute to the [[Overpopulation of domestic pets|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==
{{anchor|Methods}}
===Females (spaying)===
{{see also|Pediatric spaying}}
[[File:Spay 1.JPG|thumb|Feline uterus]]
[[File:Female dog spay incision.jpg|thumb|Closed spaying incision on a female dog, taken 24 hours after surgery]]
Spaying is the surgical removal of the ovaries and sometimes uterus in female animals. It is commonly performed as a method of birth control and [[behavior modification]].<ref name="pmid8226251">{{Cite journal
| author = Hooper R. N.
| author2 = Taylor T. S.
| author3 = Varner D. D.
| author4 = Blanchard T. L.
| title = Effects of bilateral ovariectomy via colpotomy in mares: 23 cases (1984–1990)
| journal = Journal of the American Veterinary Medical Association
| volume = 203
| issue = 7
| pages = 1043–6
|date=October 1993
| doi = 10.2460/javma.1993.203.07.1043
| pmid = 8226251
}}</ref>

In non-human animals, the technical term is an '''ovo-[[hysterectomy]]''' or '''ovariohysterectomy'''; while in humans, this is called a hystero-[[oophorectomy]]. One form of spaying is to remove only the ovaries (oophorectomy or ovariectomy), which is mainly done in [[cat]]s and young [[dog]]s as well as in laparoscopic procedures. Another, less commonly performed method is an "ovary-sparing spay"<ref>{{cite web|url=http://www.parsemusfoundation.org/ovary-sparing-spay/|title=Ovary-Sparing Spay – Parsemus Foundation|url-status=live|archive-url=https://web.archive.org/web/20151008060139/http://www.parsemusfoundation.org/ovary-sparing-spay/|archive-date=8 October 2015}}</ref> in which the uterus is removed but one (or both) ovaries are left. A '''complete ovariohysterectomy''' may involve removal of the ovaries, uterus, [[oviduct]]s, and [[uterine horns]].

[[File:Cat spay scar.jpg|thumb|Surgical incision site of a female cat]]
The surgery can be performed using [[Open surgery|a traditional open approach]] or by [[Laparoscopic surgery|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 [[Navel|umbilicus]]. 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]] 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]] (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 (abdomen)|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.<ref>{{cite journal |last1=Bartier |first1=Amanda L. |last2=Atilla |first2=Aylin |last3=Archer |first3=Rebecca |last4=Kwong |first4=Grace P. S. |title=Optimal Suture Bite Size for Closure of Feline Linea Alba—A Cadaveric Study |journal=Frontiers in Veterinary Science |date=10 December 2019 |volume=6 |article-number=441 |doi=10.3389/fvets.2019.00441|pmid=31921902 |pmc=6914685 |doi-access=free }}</ref>

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 {{convert|5|and|10|mm}} 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. 

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).

Removing the ovaries in female dogs removes the production of [[progesterone]], which is a natural calming [[hormone]] and a [[serotonin]] uplifter. Spaying may therefore escalate any observable aggressive behaviour, either to humans or other dogs.<ref name="Polsky" /><ref name="Blackshaw" /><ref name="Wright" /><ref name="Crowell" />

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)===
{{Main|Castration#Other animals}}
{{See also|Gelding}}
[[File:Neutering incision on a dog.jpg|thumb|Closed castration incision on a male dog, taken 12 hours after surgery]]
In male animals, [[castration]] involves the removal of the [[testes]] (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[ing]'' is used to specifically mean castration, e.g. in phrases like "spay and neuter".


===Sterilization alternatives===

====Hormone-Sparing Surgery====
[[Vasectomy]]: In a more delicate procedure than castration, the [[Vas deferens|vasa deferentia]] – ducts that run from the testes to the [[penis]] – are cut then tied or sealed, to prevent [[sperm]] from entering into the [[urethra]]. Failure rates are insignificantly small. [[Animal breeding|Breeders]] routinely have this procedure carried out on male [[ferret]]s and [[sheep]] 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 [[Animal show|show animals]], to cosmetically preserve their appearance (though depending upon the [[Animal fancy|fancier organization]], the procedure may invalidate the animal's candidacy for certain awards, or relegate it to a non-[[Pedigree (animal)|pedigree]], generic "household pet" competition division, just as with full castration).

[[Tubal ligation]]: Snipping and tying of [[oviduct]]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]] unchanged. Both sexes will retain their normal reproductive behavior, and other than birth control, none of the advantages and disadvantages listed below 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.

=====Injectable=====
* Male dogs – Two intratesticular injectable formulations are known to sterilize male dogs. [[Zeuterin]] was approved by the United States [[Food and Drug Administration]] (FDA) for permanent sterilization of male dogs ages three months and older by causing [[necrosis]] of the testicle.<ref>{{Cite web|url=https://www.acc-d.org/available-products/zeuterin-esterilsol|title=Zeuterin|date=5 January 2019|website=www.acc-d.org|access-date=5 January 2019}}</ref> 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.<ref>{{Cite journal|last=Leoci|first=Raffaella|date=14 October 2014|title=Alcohol diluent provides the optimal formulation for calcium chloride non-surgical sterilization in dogs|journal=Acta Veterinaria Scandinavica|volume=56|issue=1 |article-number=62|doi=10.1186/s13028-014-0062-2|pmid=25317658|pmc=4195956 |doi-access=free }}</ref>
* Male cats – Calcium chloride formulations have also been studied in male cats.<ref>{{Cite journal|last=Jana|first=Kuladip|date=2011|title=Clinical Evaluation of Non-surgical Sterilization of Male Cats with Single Intra-testicular Injection of Calcium Chloride|journal=BMC Vet Res|volume=7|page=39|pmc=3152893|pmid=21774835|doi=10.1186/1746-6148-7-39 |doi-access=free }}</ref> 
* Male rats – [[Adjudin]] ([[Analog (chemistry)|analogue]] of indazole-carboxylic acid), induces reversible germ cell loss from the [[Seminiferous tubules|seminiferous epithelium]] by disrupting cell adhesion function between [[Sertoli cell|nurse cells]] and [[Spermatogonium|immature sperm cells]], preventing [[Spermatogenesis|maturation]].
* 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<ref>{{Cite journal| first1= Martin M. |last1= Matzuk |first2= Michael R. |last2= McKeown|first3= Panagis |last3= Filippakopoulos |first4= Qinglei |last4= Li |first5= Lang |last5= Ma |first6= Julio E. |last6= Agno |first7= Madeleine E. |last7= Lemieux |first8= Sarah |last8= Picaud |first9= Richard N. |last9= Yu |first10= Jun |last10= Qi |first11= Stefan |last11= Knapp |first12= James E. |last12= Bradner | title=Small-Molecule Inhibition of BRDT for Male Contraception | journal=Cell | date=2012-08-17 | volume=150 | issue=4 | pages=673–684 | url= | doi=10.1016/j.cell.2012.06.045 | pmid=22901802 | pmc=3420011}}</ref>
* Male sheep and pigs – Wireless Microvalve.<ref>{{Cite journal |last1= Jones |first1= Inke |first2= Lucas |last2= Ricciardi |first3= Leonard |last3= Hall |first4= Hedley |last4= Hansen |first5= Vijay |last5= Varadan |first6= Chris |last6= Bertram |first7= Simon |last7= Maddocks |first8= Stefan |last8= Enderling |first9= David |last9= Saint |first10= Said |last10= Al-Sarawi |author-link11= Derek Abbott |first11= Derek |last11= Abbott |url= http://www.eleceng.adelaide.edu.au/personal/dabbott/publications/SMS_jones2008.pdf |title= Wireless RF communication in biomedical applications |journal= Smart Materials and Structures |volume= 17 |issue= 1 |date= 17 January 2008 |pages= 8–9 |doi= 10.1088/0964-1726/17/1/015050 |access-date= 2008-06-25 |url-status= live |archive-url= http://archive.wikiwix.com/cache/20110825090935/http://www.eleceng.adelaide.edu.au/personal/dabbott/publications/SMS_jones2008.pdf |archive-date= 25 August 2011 |bibcode= 2008SMaS...17a5050J |s2cid= 31682313 }}</ref> A proposed non-chemical, reversible sterilization method using a [[Piezoelectricity|piezoelectric]] [[polymer]] 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]] that occurs just after the [[epididymis]], the implantation can be carried out by use of a hypodermic needle.
* Female mammals – Vaccine of antigens (derived from purified [[porcine zona pellucida]]) encapsulated in liposomes (cholesterol and lecithin) with an adjuvant, latest US patent [https://web.archive.org/web/20061027161320/http://www.pharmcast.com/Patents/Yr2001/June2001/061201/RE37224_Fertilization061201.htm RE37,224] (as of 2006-06-06), CA patent [https://web.archive.org/web/20071029225337/http://patents1.ic.gc.ca/details?patent_number=2137363 2137263] (issued 1999-06-15). Product commercially known as SpayVac,<ref>[https://web.archive.org/web/20031214053009/http://www.spayvac.org/ SpayVac]. Retrieved on early 2003.</ref> a single injection causes a treated female mammal to produce antibodies that bind to [[Zona Pellucida|ZP3]] on the surface of her ovum, blocking sperm from fertilizing it for periods from 22 months up to 7 years (depending on the animal<ref>{{cite conference |url=https://www.aphis.usda.gov/wildlife_damage/nwrc/publications/06pubs/miller062.pdf |title=Long-term Efficacy of Three Contraceptive Approaches for Population Control of Wild Horses |first1=Gary |last1=Killian |first2=Nancy K. |last2=Diehl |first3=Lowell |last3=Miller |first4=Jack |last4=Rhyan |first5=David |last5=Thain |date=2007 |conference=22nd Vertebrate Pest Conference |editor1-last=Timm |editor1-first=R. M. |editor2-last=O'Brien |editor2-first=J. M. |book-title=Proceedings, Twenty-Second Vertebrate Pest Conference |publisher=University of California, Davis |pages=67–71 |archive-url=https://web.archive.org/web/20170213013356/https://www.aphis.usda.gov/wildlife_damage/nwrc/publications/06pubs/miller062.pdf |archive-date=13 February 2017  }}</ref><ref>{{cite web| last1=DeNicola | first1=Anthony | first2= Lowell A. |last2= Miller | first3= James P. |last3= Gionfriddo | first4= Kathleen A. |last4= Fagerstone  | publisher=Northeast Association of Fish and Wildlife Agencies | url=http://www.neafwa.org/html/wildlifeabs.shtml#d | title=Status of Present Day Infertility Technology | date=2007-03-16 | access-date=2007-03-16 |archive-url = https://web.archive.org/web/20070829131847/http://www.neafwa.org/html/wildlifeabs.shtml#d |archive-date = 29 August 2007}}</ref>). This will not prevent the animal from going into heat (ovulating) and other than birth control, none of the  advantages or disadvantages mentioned below apply.

====Other====
* Male mice – reversible regulation of the KATNAL1 gene in the Sertoli cell microtubule dynamics of the testes.<ref>{{Cite journal |first1= Lee B. |last1= Smith |first2= L. |last2= Milne |first3= N. |last3= Nelson |first4= S. |last4= Eddie |first5= P. |last5= Brown |first6= N. |last6= Atanassova |first7= M. K. |last7= O'Bryan |first8= L. |last8= O'Donnell |first9= D. |last9= Rhodes |first10= S. |last10= Wells |first11= D. |last11= Napper |first12= P. |last12= Nolan |first13= Z. |last13= Lalanne |first14= M. |last14= Cheeseman |first15= J. |last15= Peters |title= KATNAL1 Regulation of Sertoli Cell Microtubule Dynamics is Essential for Spermiogenesis and Male Fertility |date= May 2012 |url= http://www.eurekalert.org/pub_releases/2012-05/uoe-gdp052412.php |journal= PLOS Genetics |doi= 10.1371/journal.pgen.1002697 |volume= 8 |issue= 5 |article-number= e1002697 |pmid= 22654668 |pmc= 3359976 |url-status= live |archive-url= http://archive.wikiwix.com/cache/20120526133105/http://www.eurekalert.org/pub_releases/2012-05/uoe-gdp052412.php |archive-date= 26 May 2012 |doi-access= free }}</ref>
* 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.<ref>{{Cite journal| first1= Jeffrey T. |last1= Jensen |first2= Mary B. |last2= Zelinski |first3= Jessica E. |last3= Stanley |first4= John W. |last4= Fanton| first5=  Richard L. |last5= Stouffer | title=The phosphodiesterase 3 inhibitor ORG 9935 inhibits oocyte maturation in the naturally selected dominant follicle in Rhesus macaques | journal=Contraception |date=April 2008 | pages=303–7 | volume=77 | issue=4 | doi=10.1016/j.contraception.2008.01.003 | pmc=2505347| pmid=18342656 }}</ref>


"'''{{vanchor|Gomerization|reason=Redirects here. So do other terms boldfaced in this section.}}'''" is breeders' informal term for surgical techniques by which male livestock, such as bulls, retain their full [[libido]] (and related effects like sex [[pheromones]] that would be lost through castration), but are rendered incapable of [[copulation (zoology)|copulation]]. This is done to stimulate and identify [[estrous]] females without the risk of transmitting [[Sexually transmitted disease|venereal diseases]] or causing a pregnancy by a male other than the one intended for [[selective breeding]]. 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]]l penetration. '''Penile fixation''' permanently attaches the penis to the abdomen so that it cannot be lowered for penetration. [[Penectomy]] is the partial or complete removal of the [[penis]].<ref>{{cite web|url=http://www.drostproject.org/en_bovrep/2-8/itemtop56.html|title=Penectomized Teaser Bull|publisher=The Drost Project|access-date=2011-08-24|url-status=live|archive-url=https://web.archive.org/web/20120331044336/http://www.drostproject.org/en_bovrep/2-8/itemtop56.html|archive-date=31 March 2012}}</ref>


==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]]. 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%.<ref name="Kustritz"/> The [[American Veterinary Medical Association]], American Animal Hospital Association and the [[Canadian Veterinary Medical Association]] support the procedure for population control, provided that the veterinarian uses their best knowledge when making the decision about the age at neutering.<ref>{{cite web|url=http://www.avma.org/issues/policy/animal_welfare/spay_neuter.asp|title=Early-Age (Prepubertal) Spay/Neuter of Dogs and Cats|archive-url=https://web.archive.org/web/20081216034618/http://www.avma.org/issues/policy/animal_welfare/spay_neuter.asp|archive-date=16 December 2008}}</ref><ref>[https://secure.aahanet.org/eweb/DynamicPage.aspx?site=resources&webcode=referenceDetail&postKey=1bc32a74-b97d-488f-8ae9-ec013839b1c7 Early Neutering of Companion Animals Position Statement] {{webarchive|url=https://web.archive.org/web/20100713113925/http://secure.aahanet.org/eweb/DynamicPage.aspx?site=resources&webcode=referenceDetail&postKey=1bc32a74-b97d-488f-8ae9-ec013839b1c7 |date=13 July 2010 }} American Animal Hospital Association</ref><ref name="CVMA">[http://canadianveterinarians.net/ShowText.aspx?ResourceID=414 Dog and Cat Spay/Castration] {{webarchive|url=http://archive.wikiwix.com/cache/20111011003000/http://canadianveterinarians.net/ShowText.aspx?ResourceID=414 |date=11 October 2011 }} at CanadianVeterinarians.net</ref> A task force recommends that cats are spayed–neutered prior to 5 months of age.<ref>{{cite journal |last1=Mechler |first1=Esther |last2=Bushby |first2=Philip A |title=Fix by Five – an ethical responsibility? |journal=Journal of Feline Medicine and Surgery |date=25 February 2020 |volume=22 |issue=3 |page=207 |doi=10.1177/1098612X20904655|pmid=32093578 |s2cid=211477735 |doi-access= |pmc=11132591 }}</ref><ref>{{cite web |title=Feline Fix by Five Months |url=https://www.felinefixbyfive.org/ |website=Feline Fix by Five Months |access-date=26 February 2020}}</ref>

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.<ref name="spaincat">{{cite journal|title=Long-term risks and benefits of early-age gonadectomy in cats|first1=C. Victor|last1=Spain|first2=Janet M.|last2=Scarlett|first3=Katherine A.|last3=Houpt|date=1 February 2004|journal=Journal of the American Veterinary Medical Association|volume=224|issue=3|pages=372–379|doi=10.2460/javma.2004.224.372|pmid=14765796}}</ref><ref name="spaindog">{{cite journal|last1=Spain|first1=CV|last2=Scarlett|first2=JM|last3=Houpt|first3=KA|title=Long-term risks and benefits of early-age gonadectomy in dogs|journal=Journal of the American Veterinary Medical Association|date=1 February 2004|volume=224|issue=3|pages=380–7|doi=10.2460/javma.2004.224.380|pmid=14765797|s2cid=11696126|doi-access=free}}</ref><ref>{{Cite journal|pmid=11110455 |date=2000 |first1= L. M. |last1=Howe |first2=M. R. |last2=Slater |first3=H. W.|last3=Boothe  |first4=H. P. |last4=Hobson |first5=T. W. |last5=Fossum |first6=A. C. |last6=Spann |first7=W. S. |last7=Wilkie |title=Long-term outcome of gonadectomy performed at an early age or traditional age in cats |volume=217 |issue=11 |pages=1661–5 |journal=Journal of the American Veterinary Medical Association |doi=10.2460/javma.2000.217.1661 |s2cid=15153373 |doi-access=free }}</ref><ref name="howedog">{{Cite journal|pmid=11195826 |date=2001 |last1=Howe |first1=Lisa M. |first2= Margaret R. |last2= Slater |first3= Harry W. |last3= Boothe |first4= H. Phil |last4= Hobson |first5= Jennifer L. |last5= Holcom |first6= Angela C. |last6= Spann |title= Long-term outcome of gonadectomy performed at an early age or traditional age in dogs |volume=218 |issue=2 |pages=217–21 |journal=Journal of the American Veterinary Medical Association |doi=10.2460/javma.2001.218.217|citeseerx=10.1.1.204.173 }}</ref><ref name="howe">{{Cite journal|pmid=9215412 |date=1997 |author1=Howe |title=Short-term results and complications of prepubertal gonadectomy in cats and dogs |volume=211 |issue=1 |pages=57–62 |journal=Journal of the American Veterinary Medical Association|doi=10.2460/javma.1997.211.01.57 }}</ref> Anesthesia recovery in young animals is usually more rapid and there are fewer complications.<ref name="howe"/><ref>{{Cite journal|doi=10.1053/svms.2002.34328 |title=Early spay-neuter: Clinical considerations |date=2002 |last1=Kustritz |first1=M. |journal=Clinical Techniques in Small Animal Practice |volume=17 |pages=124–8 |pmid=12476815 |issue=3|s2cid=41510596 }}</ref> 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.<ref name="spaindog"/> A later study comparing female dogs spayed between 4 and 6 months and after 6 months showed no increased risk.<ref>{{Cite journal | last1 = De Bleser | first1 = B. | last2 = Brodbelt | first2 = D. C. | last3 = Gregory | first3 = N. G. | last4 = Martinez | first4 = T. A. | title = The association between acquired urinary sphincter mechanism incompetence in bitches and early spaying: A case-control study | journal = The Veterinary Journal | volume = 187 | issue = 1 | pages = 42–47 | year = 2009 | pmid = 20004121 | doi = 10.1016/j.tvjl.2009.11.004| url = https://researchonline.rvc.ac.uk/id/eprint/5931/1/5931.pdf }}</ref>

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.<ref name="spaindog"/> Another study showed no correlation between age of neutering and musculoskeletal problems.<ref name="howedog"/> A study of large breed dogs with [[cranial cruciate ligament]] rupture associated early-age neutering with the development of an excessive tibial plateau angle.<ref>{{Cite journal|pmid=18052804 |doi=10.2460/javma.231.11.1688 |date=2007 |author1=Duerr |first2=C. G. |first3=R. S. |first4=R. D. |first5=E. L. |first6=R. H. |title=Risk factors for excessive tibial plateau angle in large-breed dogs with cranial cruciate ligament disease |volume=231 |issue=11 |pages=1688–91 |journal=Journal of the American Veterinary Medical Association |last2=Duncan |last3=Savicky |last4=Park |last5=Egger |last6=Palmer|doi-access=free }}</ref>

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".<ref>{{cite journal|title=Neutering dogs |journal=PLOS ONE |volume=8 |issue=2 |article-number=e55937 |doi=10.1371/journal.pone.0055937 |pmid=23418479 |pmc=3572183 |year = 2013|last1 = Torres de la Riva|first1 = Gretel|last2=Hart |first2=Benjamin L. |last3=Farver |first3=Thomas B. |last4=Oberbauer |first4=Anita M. |last5=Messam |first5=Locksley L. McV. |last6=Willits |first6=Neil |last7=Hart |first7=Lynette A. |bibcode=2013PLoSO...855937T |doi-access=free }}</ref>

The second study from 2014<ref>{{cite journal |title=Long-Term Health Effects of Neutering Dogs: Comparison of Labrador Retrievers with Golden Retrievers |journal=PLOS ONE |volume=9 |issue=7 |article-number=e102241  |doi=10.1371/journal.pone.0102241 |pmid=25020045 |pmc=4096726 |year = 2014|last1 = Hart|first1 = Benjamin L.|last2=Hart |first2=Lynette A. |last3=Thigpen |first3=Abigail P. |last4=Willits |first4=Neil H. |bibcode=2014PLoSO...9j2241H |doi-access=free }}</ref> 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 in dogs|separation anxiety]], aggression, escape behavior and inappropriate elimination are reduced with neutering while noise phobia and sexual behavior has been shown to potentially increase.{{Citation needed|date=January 2025}} In males with aggression issues, earlier neutering may increase barking.<ref name="spaindog"/> 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.<ref name="spaincat"/>

==Health and behavioral effects==
{{procon|date=April 2017}}
{{see also|Castration#Medical consequences}}

===Advantages===
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.<ref>{{cite journal |last1=Farhoody |first1=Parvene |title=Aggression toward Familiar People, Strangers, and Conspecifics in Gonadectomized and Intact Dogs |journal=Frontiers in Veterinary Science |date=26 February 2018 |volume=5 |article-number=18 |doi=10.3389/fvets.2018.00018 |pmid=29536014 |pmc=5834763 |doi-access=free }}</ref>  Sexual behavior in cats seems to make them especially undesirable to pet owners.<ref name="Kustritz">{{cite journal |title=Determining the Optimal age for Gonadectomy of Dogs and Cats | doi=10.2460/javma.231.11.1665 |date= 2007 |last1= Kustritz |first1= Margaret V. Root |journal= Journal of the American Veterinary Medical Association |volume= 231 |issue= 11 |pages= 1665–75 |pmid= 18052800| s2cid=4651194 | url=https://semanticscholar.org/paper/0d15d47bace395843f23fc8eef127dcbfc22bf82 |doi-access= free }}</ref>
* 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.<ref>{{cite web|last1=Poulton|first1=Gerry|title=Mammary Tumours in Dogs|url=http://www.vef.unizg.hr/org/kirurgija/wp-content/uploads/2010/04/CESA_January_2009.pdf.pdf|publisher=Irish Veterinary Journal|url-status=live|archive-url=https://web.archive.org/web/20150402120904/http://www.vef.unizg.hr/org/kirurgija/wp-content/uploads/2010/04/CESA_January_2009.pdf.pdf|archive-date=2 April 2015}}</ref>
* Neutering increases life expectancy in cats: one study found castrated male cats live 62% longer than intact males, while spayed female cats live 39% longer than intact females.<ref> [https://www.humanesociety.org/resources/why-you-should-spayneuter-your-pet The Humane Society of the United States]</ref> 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.{{Citation needed|date=February 2023}}
* 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.<ref>{{cite web |url=http://www.ivis.org/advances/concannon/gobello/ivis.pdf |title=Canine Pseudopregnancy: A Review |first=C. |last=Gobello |date=23 August 2001 |work=IVIS.org |publisher=International Veterinary Information Service |access-date=13 April 2010 |display-authors=etal |archive-url=https://web.archive.org/web/20110419121323/http://www.ivis.org/advances/concannon/gobello/ivis.pdf |archive-date=19 April 2011  }}</ref>
* [[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 female dog developing pyometra by age 10 is 25% across all breeds, but can be as high as 54% in some breeds.<ref>{{cite journal|title=Breed Risk of Pyometra in Insured Dogs in Sweden|journal=Journal of Veterinary Internal Medicine| doi=10.1111/j.1939-1676.2001.tb01587.x|volume=15|issue=6|pages=530–538|year=2001|last1=Egenvall|first1=Agneta|last2=Hagman|first2=Ragnvi|last3=Bonnett|first3=Brenda N.|last4=Hedhammar|first4=Ake|last5=Olson|first5=Pekka|last6=Lagerstedt|first6=Anne-Sofie|pmid=11817057|doi-access=}}</ref> 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%.<ref>{{cite journal|title=Results and complications of surgical treatment of pyometra: a review of 80 cases|journal=[[Journal of the American Animal Hospital Association]]|url=http://cel.webofknowledge.com/InboundService.do?product=CEL&SID=T2VUDVHmOxrj332hibj&UT=WOS%3AA1989AR48200015&SrcApp=Highwire&action=retrieve&Init=Yes&SrcAuth=Highwire&Func=Frame&customersID=Highwire&IsProductCode=Yes&mode=FullRecord|archive-url=https://archive.today/20150319014740/http://cel.webofknowledge.com/InboundService.do?product=CEL&SID=T2VUDVHmOxrj332hibj&UT=WOS:A1989AR48200015&SrcApp=Highwire&action=retrieve&Init=Yes&SrcAuth=Highwire&Func=Frame&customersID=Highwire&IsProductCode=Yes&mode=FullRecord|archive-date=2015-03-19}}</ref> 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.

===Disadvantages===
* 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.<ref>{{Cite journal|pmid=18466167 |date=2008 |author1=Brodbelt |first2=K. J. |first3=R. A. |first4=P. J. |first5=L. E. |first6=D. U. |first7=J. L. |title=The risk of death: the confidential enquiry into perioperative small animal fatalities |volume=35 |issue=5 |pages=365–73 |doi=10.1111/j.1467-2995.2008.00397.x |journal=Veterinary Anaesthesia and Analgesia |last2=Blissitt |last3=Hammond |last4=Neath |last5=Young |last6=Pfeiffer |last7=Wood|s2cid=22017193 |url=https://researchonline.rvc.ac.uk/id/eprint/1370/1/1370.pdf }}</ref>
* 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.<ref name="PMID18774325">{{cite journal | pmid = 18774325 | doi=10.1016/j.jfms.2008.07.002 | volume=11 | issue=2 | title=Prevalence and risk factors of obesity in an urban population of healthy cats |date=February 2009 | journal=Journal of Feline Medicine and Surgery | pages=135–40 | author=Colliard L. | author2=Paragon B. M. | author3=Lemuet B.| author4=Bénet J. J. | author5=Blanchard G.| s2cid=25617418 | doi-access=free | pmc=10832791 }}</ref> In cats, a decrease in sex hormone levels seems to be associated with an increase in food intake.<ref name="PMID17845247">{{cite journal | pmid = 17845247 | doi=10.1111/j.1439-0396.2006.00667.x | volume=91 | issue=9–10 | title=Oestradiol, but not genistein, inhibits the rise in food intake following gonadectomy in cats, but genistein is associated with an increase in lean body mass |date=October 2007 | journal=Journal of Animal Physiology and Animal Nutrition | pages=400–10 | author=Cave N. J. | author2=Backus R. C. | author3=Marks S. L.| author4=Klasing K. C.}}</ref> In dogs, the effects of neutering as a risk factor for obesity vary among breeds.<ref name="PMID15923551">{{cite journal | pmid = 15923551 | volume=156 | issue=22 | title=Prevalence of obesity in dogs examined by Australian veterinary practices and the risk factors involved |date=May 2005 | journal=Veterinary Record | pages=695–702 | author=McGreevy P. D. | author2=Thomson P. C. | author3=Pride C.| author4=Fawcett A. | author5=Grassi T.| author6=Jones B. | doi=10.1136/vr.156.22.695| s2cid=36725298 }}</ref>
* 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.<ref name=Priester>{{Cite journal|pmid=7254313 |date=1980 |author1=Priester |first2=F. W. |title=The Occurrence of Tumors in Domestic Animals |issue=54 |pages=1–210 |journal=National Cancer Institute Monograph |last2=McKay}}</ref><ref name=Ru>{{Cite journal|doi=10.1016/S1090-0233(98)80059-2 |title=Host related risk factors for canine osteosarcoma |date=1998 |last1=Ru |first1=G. |first2=B. |first3=L. |journal=The Veterinary Journal |volume=156 |pages=31–9 |pmid=9691849 |issue=1 |last2=Terracini |last3=Glickman}}</ref><ref name=Cooley>{{Cite journal|author=Cooley, D. M.|author2=Beranek, B. C.|date=1 November 2002|title=Endogenous gonadal hormone exposure and bone sarcoma risk|journal=Cancer Epidemiology, Biomarkers & Prevention|url=http://cebp.aacrjournals.org/cgi/content/full/11/11/1434|pmid=12433723|volume=11|issue=11|pages=1434–40|display-authors=etal|url-status=live|archive-url=https://web.archive.org/web/20030825175957/http://cebp.aacrjournals.org/cgi/content/full/11/11/1434|archive-date=25 August 2003}}</ref>
* 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.<ref name=Prymak>{{Cite journal |author=Prymak C. |author2=McKee L. J. |author3=Goldschmidt M. H.|author4=Glickman L. T. |date=1988 |title=Epidemiologic, clinical, pathologic, and prognostic characteristics of splenic hemangiosarcoma and splenic hematoma in dogs: 217 cases (1985) |journal= Journal of the American Veterinary Medical Association |volume=193 |issue=6 |pages=706–712 |doi=10.2460/javma.1988.193.06.706 |pmid=3192450}}</ref><ref name=Ware>{{Cite journal|doi=10.1892/0891-6640(1999)013<0095:CTID>2.3.CO;2 |pmid=10225598 |title=Cardiac Tumors in Dogs: 1982–1995 |date=1999 |last1=Ware |first1=Wendy A. |last2=Hopper |first2=David L. |journal=Journal of Veterinary Internal Medicine |volume=13 |issue=2 |pages=95–103 |doi-broken-date=23 September 2025 }}</ref>
* Spaying and castrating is associated with an increase in urinary tract cancers in dogs, however the risk is still less than 1%.<ref name=Sanborn>{{cite web |author=Sanborn, L. J. |title=Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs |url=http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf |date=14 May 2007 |access-date=13 April 2010 |url-status=live |archive-url=https://web.archive.org/web/20100107141430/http://www.naiaonline.org/pdfs/longtermhealtheffectsofspayneuterindogs.pdf |archive-date=7 January 2010  }}</ref>
* 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%.<ref name=Moore>{{Cite journal |author=Moore G. E. |author2=Guptill L. F. |author3=Ward M. P.|author4=Glickman N. W. |author5=Faunt K. F.|author6=Lewis H. B. |author7=Glickman L.T. |date=2005 |title=Adverse events diagnosed within three days of vaccine administration in dogs|journal= Journal of the American Veterinary Medical Association |volume=227 |issue=7 |pages=1102–1108 |doi=10.2460/javma.2005.227.1102 |pmid=16220670|s2cid=8625559 |doi-access=free }}</ref>
* Neutered dogs have been known to develop hormone-responsive [[alopecia]] (hair loss).<ref>{{Cite web|url=https://m.petmd.com/dog/conditions/endocrine/c_dg_hormone_responsive_dermatoses|title=Baldness and Hormone-Related Skin Disorders in Dogs|website=m.petmd.com|access-date=2019-12-28|archive-date=15 June 2016|archive-url=https://web.archive.org/web/20160615162844/https://m.petmd.com/dog/conditions/endocrine/c_dg_hormone_responsive_dermatoses}}</ref>
* 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.<ref>{{cite journal |last1=Slauterbeck |first1=J. R. |author2=Pankratz, K. |author3=Xu, K. T. |author4=Bozeman, S. C. |author5= Hardy, D. M.  |title=Canine Ovariohysterectomy and Orchiectomy Increases the Prevalence of ACL Injury |journal=Clinical Orthopaedics and Related Research |date=Dec 2004 |volume=429 |issue=429 |pages=301–5|doi=10.1097/01.blo.0000146469.08655.e2 |pmid=15577502 |s2cid=23047078 }}</ref>
* 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]].<ref>{{cite journal|last=Torres de la Riva|first=Gretel|title=Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers|doi=10.1371/journal.pone.0055937|pmid=23418479|pmc=3572183|journal=PLOS ONE|volume=8|issue=2|article-number=e55937|year=2013|bibcode=2013PLoSO...855937T|doi-access=free}}</ref>
* Castration and spaying can increase the risk of geriatric cognitive impairment.<ref name=Sanborn />
* About 2% of castrated [[male dogs]] eventually develop [[prostate cancer]], compared to less than 0.6% of intact males.<ref name=Teske>{{Cite journal|doi=10.1016/S0303-7207(02)00261-7 |title=Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs |date=2002 |last1=Teske |first1=E. |journal=Molecular and Cellular Endocrinology |volume=197 |pages=251–5 |pmid=12431819 |first2=E. C. |first3=E. M. |first4=E. |first5=J. A. |issue=1–2 |last2=Naan |last3=Van Dijk |last4=Van Garderen |last5=Schalken|s2cid=7080561 }}</ref><ref name=Sorenmo>{{Cite journal|doi=10.1046/j.1476-5829.2003.00007.x |title=Immunohistochemical characterization of canine prostatic carcinoma and correlation with castration status and castration time |date=2003 |last1=Sorenmo |first1=K. U. |first2=M. |first3=F. |first4=C. |first5=J. |journal=Veterinary and Comparative Oncology |volume=1 |pages=48–56 |pmid=19379330 |issue=1 |last2=Goldschmidt |last3=Shofer |last4=Goldkamp |last5=Ferracone}}</ref> The evidence is most conclusive for [[Bouvier des Flandres|Bouviers]].<ref name=Sanborn/>
* 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.<ref>{{Cite journal|pmid=11439769 |doi=10.2460/javma.2001.219.51 |date=2001 |author1=Hart |title=Effect of gonadectomy on subsequent development of age-related cognitive impairment in dogs |volume=219 |issue=1 |pages=51–6 |journal=Journal of the American Veterinary Medical Association|s2cid=17565731 |doi-access=free }}</ref>
* 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.<ref>{{Cite journal|pmid=11345305 |doi=10.2460/javma.2001.218.1429 |date=2001 |author1=Lekcharoensuk |first2=C. A. |first3=J. P. |title=Epidemiologic study of risk factors for lower urinary tract diseases in cats |volume=218 |issue=9 |pages=1429–35 |journal=Journal of the American Veterinary Medical Association |last2=Osborne |last3=Lulich|doi-access=free }}</ref>
* Neutering has been associated with an increased likelihood of urethral sphincter incontinence in male dogs.<ref>{{cite journal | last1 = Aaron | first1 = A. | last2 = Eggleton | first2 = K. | last3 = Power | first3 = C. | last4 = Holt | first4 = P. E. | title = Urethral sphincter mechanism incompetence in male dogs: a retrospective analysis of 54 cases | journal = Veterinary Record | volume = 139 | issue = 22 | pages= 542–6| year = 1996 | doi=10.1136/vr.139.22.542| pmid = 8961524 | s2cid = 5642622 }}</ref>
* 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.<ref name="Beauvais">{{Cite journal | last1 = Beauvais | first1 = W. | last2 = Cardwell | first2 = J. M. | last3 = Brodbelt | first3 = D. C. | doi = 10.1111/j.1748-5827.2011.01176.x | title = The effect of neutering on the risk of urinary incontinence in bitches - a systematic review | journal = Journal of Small Animal Practice | volume = 53 | issue = 4 | pages = 198–204 | year = 2012 | pmid =  22353203| url = https://animalstudiesrepository.org/cgi/viewcontent.cgi?article=1002&context=endoc }}</ref><ref>{{Cite web|url=https://www.merck-animal-health-usa.com/dp/49|title=Merck Animal Health USA|website=www.merck-animal-health-usa.com|access-date=2019-12-14}}</ref>
* Spayed female dogs are at an increased risk of [[hypothyroidism]].<ref name=Panciera>{{Cite journal |author=Panciera D. L. |date=1994 |title=Hypothyroidism in dogs: 66 cases (1987–1992) |journal= Journal of the American Veterinary Medical Association |volume=204 |issue=5 |pages=761–767|doi=10.2460/javma.1994.204.05.761 |pmid=8175472 }}</ref>

===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.<ref>{{Cite journal|author=Kobelt A. J.|author2=Hemsworth P. H.|author3=Barnett J. L.|author4=Coleman G. J. |title=A survey of dog ownership in suburban Australia-conditions and behaviour problems |journal=Applied Animal Behaviour Science |date=2003 |volume=82 |pages=137–148 |doi=10.1016/S0168-1591(03)00062-5|issue=2}}</ref><ref name="Casey">{{Cite journal|author=Casey R. A.|author2=Loftus B.|author3=Bolster C.|author4=Richards G. J.|author5=Blackwell E. J. |title=Human directed aggression in domestic dogs (Canis familiaris): Occurrence in different contexts and risk factors |journal=Applied Animal Behaviour Science |date=March 2014  | volume=152 |pages=52–63 |doi=10.1016/j.applanim.2013.12.003|hdl=10983/14199|hdl-access=free}}</ref> One study reported results of aggression towards familiar and strange people and other dogs reduced between 10 and 60 percent of cases,<ref>[http://www.associationofanimalbehaviorprofessionals.com/effects_of_neutering.html The Effects of Spaying and Neutering on Canine Behavior] {{webarchive|url=https://web.archive.org/web/20141022175541/http://www.associationofanimalbehaviorprofessionals.com/effects_of_neutering.html |date=22 October 2014 }} James O'Heare, Association of Animal Behavior Professionals</ref> while other studies reported increases in possessive aggression<ref>{{Cite journal|author=Guy N. C.|author2=Luescher U. A.|author3=Dohoo S. E.|author4=Spangler E.|author5=Miller J. B|author6=Dohoo I. R.|author7=Bate L. A. |title=A case series of biting dogs: characteristics of the dogs, their behaviour, and their victims |journal=Applied Animal Behaviour Science |date=2001 |volume=74 |pages=15–57 |doi=10.1016/S0168-1591(01)00155-1}}</ref> and aggression towards familiar and strange people,<ref name="Takeuchi">{{Cite journal|author=Takeuchi Y.|author2= Ogata N.|author3=Houpt J. A.|author4=Scarlett J. M. |title=Differences in background and outcome of three behavior problems of dogs |journal=Applied Animal Behaviour Science |date=2001 |volume=70 |pages=297–308 |doi=10.1016/S0168-1591(00)00156-8 |pmid=11179553 |issue=4}}</ref> and more studies reported there was no significant difference in aggression risk between neutered and non-neutered males.<ref name="Casey"/><ref>{{Cite journal|author=Neilson J.|author2=Eckstein R.|author3=Hart B. |title=Effects on castration on problem behaviors in male dogs with reference to age and duration of behavior |journal=Journal of the American Veterinary Medical Association |date=1997 |volume=211 |issue=2 |pages=180–182 |doi=10.2460/javma.1997.211.02.180 |pmid=9227747}}</ref> For females with existing aggression, many studies reported increases in aggressive behavior<ref name="Polsky">{{Cite journal|author=Polsky R. H. |title=Recognizing dominance aggression in dogs |journal=Veterinary Medicine |date=1996 |volume=91 |pages=196–201}}</ref><ref name="Blackshaw">{{Cite journal|author=Blackshaw, J.K. |title=An overview of types of aggressive behavior in dogs and methods of treatment |journal=Applied Animal Behaviour Science |date=1991 |volume=30 |pages=351–361 |doi=10.1016/0168-1591(91)90140-S|issue=3–4}}</ref><ref name="Wright">{{Cite journal|author=Wright J. C. |title=Canine aggression toward people. Bite scenarios and prevention |journal=Veterinary Clinics of North America: Small Animal Practice |date=1991 |volume=21 |issue=2 |pages=299–314 |pmid=2053252 |doi=10.1016/s0195-5616(91)50034-6}}</ref><ref name="Crowell">{{Cite journal|author=Crowell-Davis S. L. |title=Identifying and correcting human-directed dominance aggression of dogs |journal=Veterinary Medicine |date=1991 |volume=86 |pages=990–998}}</ref> and some found increased separation anxiety behavior.<ref name="Takeuchi"/><ref>{{Cite journal|author=Podberscek A. L.|author2=Serpell J. A. |title=The English Cocker Spaniel: preliminary findings on aggressive behaviour |journal=Applied Animal Behaviour Science |date=1996 |volume=47 |issue=1–2 |pages=75–89 |doi=10.1016/0168-1591(95)01012-2}}</ref> 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.<ref>Meuten D. J. ''Tumors in Domestic Animals''. 4th Edn. Iowa State Press, Blackwell Publishing Company, Ames, Iowa, p. 575</ref> Early age gonadectomy is associated with an increased incidence of noise phobias and {{clarify span|undesirable sexual behaviors|date=September 2013}}.<ref>{{cite journal | author = Spain C. V. | author2 = Scarlett J. M. | author3 = Houpt K. A. | date = 2004 | title = Long-term risks and benefits of early-age gonadectomy in dogs | journal = Journal of the American Veterinary Medical Association | volume = 224 | issue = 3| pages = 380–387 | doi = 10.2460/javma.2004.224.380 | pmid = 14765797 | s2cid = 11696126 | doi-access = free }}</ref>

==Terminology for neutered animals==
A specialized vocabulary is used in [[animal husbandry]] and [[animal fancy]] for neutered (castrated) animals:
{{glossary}}
{{term |1=barrow}}
{{defn |1=[[Pig]] castrated before maturity.<ref name="Romich 2013"/>}}
{{term |1=bullock}}
{{defn |1=Male castrated [[Working animal|draft animal]].<ref name = "Campbell 1990">{{cite book|last1=Campbell|first1=Joseph K.|title=Dibble sticks, donkeys, and diesels: machines in crop production|date=1990|publisher=International Rice Research Institute|location=Manila, Philippines|isbn=978-971-10-4185-4}}</ref>}}
{{term |1=[[capon]]}}
{{defn |1=Male castrated [[chicken]].<ref name="Romich 2013"/>}}
{{term |1=[[gelding]]}}
{{defn |1=Male castrated horse,<ref>{{cite book|last1=Hasheider|first1=P|last2=Johnson|first2=S|title=The Complete Illustrated Guide to Farming|date=2014|publisher=MBI Publishing Company|isbn=978-1-62788-137-1|page=85}}</ref> or donkey.}}
{{term |1=gib}}
{{defn |1=Male castrated [[cat]],<ref name="Vanhorn 2012">{{cite book|last1=Vanhorn|first1=B|last2=Clark|first2=R|page=123|title=Veterinary Assisting Fundamentals & Applications|date=2012|publisher=Cengage Learning|isbn=978-1-133-41704-0}}</ref> or [[ferret]].<ref name="Romich 2013">{{cite book|last1=Amundson Romich|first1=J|title=An Illustrated Guide to Veterinary Medical Terminology|chapter=Chapter 5: What's in a name|date=2013|pages=115–126|publisher=Cengage Learning|edition=4th|isbn=978-1-133-70945-9}}</ref>}}
{{term |1=havier}}
{{defn |1=Male castrated [[deer]].<ref>{{cite book|editor1-last=Peek|editor1-first=Hedley|editor2-last=Aflalo|editor2-first=Frederick George|title=The Encyclopaedia of Sport, Volume 1|date=1897|publisher=Lawrence and Bullen|location=London|page=573|url=https://books.google.com/books?id=sZE-AQAAMAAJ}}</ref>}}
{{term |1=lapin}}
{{defn |1=Male castrated [[rabbit]].<ref name="Romich 2013"/>}}
{{term |1=[[ox]]}}
{{defn |1=Male castrated [[Working animal|draft animal]].<ref name = "Campbell 1990"/>}}
{{term |1=spay}}
{{defn |1=Female neutered cat.<ref name="Vanhorn 2012"/>}}
{{term |1=poulard}}
{{defn |1=Female spayed chicken.<ref name="Romich 2013"/>}}
{{term |1=sprite}}
{{defn |1=Female neutered [[ferret]].<ref name="Romich 2013"/>}}
{{term |1=steer}}
{{defn |1=Male [[cattle]] castrated before maturity.<ref name="Romich 2013"/>}}
{{term |1=stag}}
{{defn |1=Male [[cattle]] or pig castrated after maturity.<ref name="Romich 2013"/>}}
{{term |1=wether}}
{{defn |1=Male castrated [[goat]] or [[sheep]].<ref name="Romich 2013"/>}}
{{glossary end}}

==Religious views==

===Islam===
There are differing views in [[Islam]] with regard to neutering animals, with some Islamic associations stating that when done to maintain the health and welfare of both the animals and the community, neutering is allowed on the basis of being in the interest of '[[maslaha]]' (general good)<ref>{{cite web|url=http://www.catwelfare.org/page/id/23#S19|title=What some religions say about sterilisation.|archive-url=https://web.archive.org/web/20080317003815/http://www.catwelfare.org/page/id/23#S19|archive-date=17 March 2008|access-date=8 March 2008}}</ref> or "choosing the lesser of two evils".<ref>http://www.spca.org.my/neuter.htm#5 {{webarchive|url=https://web.archive.org/web/20080113173847/http://www.spca.org.my/neuter.htm |date=13 January 2008 }} Spaying/Neutering Information</ref>

===Judaism===
[[Orthodox Judaism]] forbids the castration of both humans and non-human animals by Jews,<ref>{{cite web|url=http://www.jewishsf.com/content/2-0-/module/displaystory/story_id/11109/edition_id/213/format/html/displaystory.html|title=What does Jewish law say about neutering male pets?|url-status=live|archive-url=https://web.archive.org/web/20080314152757/http://www.jewishsf.com/content/2-0-/module/displaystory/story_id/11109/edition_id/213/format/html/displaystory.html|archive-date=14 March 2008}}</ref> except in lifesaving situations.<ref>{{Cite book|author=Feinstein, Moshe|title=Igrot Moshe|author-link=Moshe Feinstein}}</ref> 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.<ref>{{cite web|url=http://www.chai.org.il/en/companion/overpopulation_sn_crucial.htm|title=CHAI – Why Spay/Neuter is Crucial|website=www.chai.org.il|url-status=live|archive-url=https://web.archive.org/web/20080315003915/http://www.chai.org.il/en/companion/overpopulation_sn_crucial.htm|archive-date=15 March 2008}}</ref>

==See also==
* [[Animal population control]]
* [[Animal shelter]]
* [[Cruelty to animals]]
* [[Hysterectomy]]
* [[Oophorectomy]]
* [[Overpopulation in companion animals]]
* [[Wildlife contraceptive]]
* [[World Spay Day]]

==References==
{{Reflist}}

==External links==
{{Wiktionary}}
{{wiktionary|spaying}}
* [http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf DVM Article on health effects of spay/neuter: Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs]
* [http://avmajournals.avma.org/doi/pdf/10.2460/javma.231.11.1665 Determining the optimal age for gonadectomy of dogs and cats, AVMA (pdf)]
* [https://lbah.com/canine/spay-canine/ Canine Spay Photos and Description]

[[Category:Castration]]
[[Category:Veterinary castration]]
[[Category:Dog health]]
[[Category:Surgical removal procedures]]
[[Category:Cat health]]
[[Category:Animal welfare]]