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Neutering, from the Latin neuter (neither), is the removal of an animal's reproductive organ, either all of it or a considerably large part of it. It is the most drastic surgical procedure with sterilizing purposes. The process is also referred to as castration for males and as spaying for females. Colloquially, it is often referred to as fixing. In male horses, the process is referred to as gelding.

Unlike in humans, neutering is the most common sterilizing method in animals. While many agree on the advantages of neutering as a method of birth control, the necessity and humanity of this method (as opposed to alternative methods of birth control) and the political agendas within the debate are a subject of some controversy. In the USA, most humane societies, animal shelters and rescue groups (not to mention numerous commercial entities) urge pet owners to have their pets "spayed or neutered" to prevent the births of unwanted litters, contributing to the overpopulation of animals. In Europe, the procedure is less commonly performed, especially in dogs.

Health and behavioral effectsEdit


In addition to being a birth control method, neutering has health benefits. Hormone-associated diseases such as benign prostatic hypertrophy are prevented. Female cats and dogs are seven times more likely to develop mammary tumors if they are not spayed before their first heat cycle.[1] A dangerous common uterine infection known as pyometra is also prevented. Uterine, ovarian, and testicular cancer are also prevented for obvious reasons, although these types of cancer are uncommon to begin with.

The procedure may end or curb such behaviors as roaming in search of a mate and sexual mounting, especially when performed in animals that have not yet reached puberty. Depending on their environment, dogs which are less prone to escaping from their yard and/or roaming are also less likely to be lost, stolen, or hit by a car.



  • As with any surgical procedure, immediate complications of neutering include the usual anesthetic and surgical complications, such as bleeding and infection. These risks are relatively low in routine spaying and neutering; however, they may be increased for some animals due to other pre-existing health factors.
  • Neutered dogs and cats of both genders may have an increased risk of obesity. Theories for this include reduced metabolism, reduced activity, and eating more due to altered feeding behavior.[2].
  • Neutered dogs of both genders are at a twofold excess risk to develop osteosarcoma as compared to intact dogs[3],[4][5] as well as an increased risk of hemangiosarcoma[6][7] and urinary tract cancer.[8]
  • Neutered dogs of both genders have an increased risk of adverse reactions to vaccinations.[9]
  • Neutered dogs have also been known to develop hormone-responsive alopecia (hair loss).[10]

Specific to MalesEdit

  • In addition, neutered male dogs are at higher risk than intact males of developing moderate to severe geriatric cognitive impairment (geriatric cognitive impairment includes 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).[13]

Specific to FemalesEdit


Obviously, most animals lose their libido due to the hormonal changes involved with both genders, and females no longer experience heat cycles, which are sometimes considered a major nuisance factor, especially in female cats. Minor personality changes may occur in the animal. Neutering is often recommended in cases of undesirable behavior in dogs, although studies suggest that while roaming, urine marking, and mounting are reduced in neutered males, it has little effect on aggression and other important behavioral issues.[19] Intact male cats are more prone to urine spraying, while many common behavioral causes of urine marking remain in castrated cats.


Females (spaying)Edit

In female animals, spaying involves abdominal surgery to remove the ovaries and uterus (ovario-hysterectomy). Alternatively, it is also possible to remove the ovaries and leave the uterus inside (ovariectomy), which is mainly done in cats and young female dogs. Spaying is commonly practiced on household pets such as cats and dogs as a method of birth control, but is rarely performed on livestock.

The surgery is usually performed through a ventral (belly) midline incision below the umbilicus (belly button). 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.

File:Spay 1.JPG

There is a ligament that attaches the ovaries to the kidneys which may need to be broken so the ovaries can be identified. The ovarian arteries are then ligated twice (tied-off) with resorbable suture material and then the arteries transected (cut). 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 3 layer closure. The linea alba (muscle layer) and then the subcutaneous layer (fat under skin) are closed with resorbable suture material. The skin is then stapled, sutured, or glued closed.

See also oophorectomy and hysterectomy.

Males (castration)Edit

In male animals, castration involves the removal of the testes, and is commonly practiced on both household pets (for birth control) and on livestock (for birth control, as well as to improve commercial value).

For more information, see castration and gelding (specific to horses).

Nonsurgical alternativesEdit


  • Male dogs - Neutersol (Zinc gluconate neutralized by arginine). Cytotoxic; produces infertility by chemical disruption of the testicle. It is no longer produced.
  • 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 and immature sperm cells, preventing maturation.
  • Male sheep and pigs - Wireless Microvalve.[20] Using a piezoelectric polymer that will deform when exposed to a specific electric field broadcast from a key fob (like a car alarm) the valve will 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 RE37,224 (as of 2006-06-06), CA patent 2137263 (issued 1999-06-15). Product commercially known as SpayVac,[21] a single injection causes a treated female mammal to produce antibodies that bind to 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[22][23]). 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.


  • Noninvasive vasectomy using ultrasound.[24]

Surgical alternatives Edit

Vasectomy: The snipping and tying of the vasa deferentia (plural of vas deferens). Failure rates are insignificantly small. This procedure is routinely carried out on male ferrets and sheep to manipulate the estrus cycles of in-contact females. It is uncommon in other animal species.

Tubal Ligation: Snipping and tying of fallopian tubes as a sterilization measure can be performed on female cats and dogs. Risk of unwanted pregnancies is insignificantly small. Only a few veterinarians will 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 above apply. This method is favored by some of the people who want to infringe on the natural state of companion animals as little as necessary to achieve the reduction of unwanted births of cats and dogs.

Penile translocation is sometimes performed in cattle to produce a "teaser bull", which retains its full libido, but is incapable of intromission. This is done to identify estrous cows without the risk of transmitting venereal diseases. [1]

Terminology for neutered animalsEdit

Male animalsEdit

Neutered males of given animal species sometimes have specific names:

Female animalsEdit

A specialized vocabulary in animal husbandry and fancy has arisen for spayed females of given animal species:

Religious views on neuteringEdit


Traditional interpretations of Orthodox Judaism forbids the castration of both humans and animals by Jews,[25] except in lifesaving situations.[26] In 2007, the Sephardic Chief Rabbi of Israel Rabbi Shlomo Amar issued a ruling stating that it is permissible to have companion animals spayed or neutered on the basis of the Jewish mandate to prevent cruelty to animals.[27]


While there are differing views in Islam with regard to neutering animals,[28] some Islamic association 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 'maslahat' (general good)[29] or "choos[ing] the lesser of two evils".[30]




  • TV celebrities Bob Barker and Drew Carey helped to popularize the spay-or-neuter drive by closing every episode of The Price Is Right with a request for people to help control the pet population by spaying or neutering their pets. In the movie Shrek 2, Donkey proposed that Puss in Boots be given the "Bob Barker Treatment", an indirect reference to neutering.


  1. Morrison, Wallace B. (1998). Cancer in Dogs and Cats (1st ed.). Williams and Wilkins. ISBN 0-683-06105-4. 
  2. German AJ (2006). "The growing problem of obesity in dogs and cats". J. Nutr. 136 (7 Suppl): 1940S–1946S. PMID 16772464. 
  3. Priester, W. A. and McKay, F. W. (1980). "The occurrence of tumors in domestic animals". Natl Cancer Inst Monograph 54: 169. 
  4. Ru, B., Terracini, G. et al. (1998). "Host related risk factors for canine osteosarcoma". Vet J 156(1):31-9 156: 31. doi:10.1016/S1090-0233(98)80059-2. 
  5. Cooley, D. M., Beranek, B. C. et al. (2002). "Endogenous gonadal hormone exposure and bone sarcoma risk". Cancer Epidemiol Biomarkers Prev 11(11): 1434-40. PMID 12433723. 
  6. Prymak C, McKee LJ, Goldschmidt MH, Glickman LT. (1988). "Epidemiologic, clinical, pathologic, and prognostic characteristics of splenic hemangiosarcoma and splenic hematoma in dogs: 217 cases (1985)". J Am Vet Med Assoc. 193 (6): 706–712. 
  7. Ware WA, Hopper DL (1999). "Cardiac Tumors in Dogs". J Vet Intern Med. 13: 95–103. doi:10.1892/0891-6640(1999)013<0095:CTID>2.3.CO;2. 
  8. Sanborn, L.J. (2007). Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs.
  9. Moore GE, Guptill LF, Ward MP, Glickman NW, Faunt KF, Lewis HB, Glickman LT. (2005). "Adverse events diagnosed within three days of vaccine administration in dogs". J Am Vet Med Assoc. 227 (7): 1102–1108. doi:10.2460/javma.2005.227.1102. 
  10. Ettinger, Stephen J.;Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine(4th ed.). W.B. Saunders Company. ISBN 0-7216-6795-3. 
  11. Teske E, Nann EC, van Dijk EM, van Garderen E, Schalken JA (2002). "Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs". Mol Cell Endocrinol. 197 (1-2): 251–255. doi:10.1016/S0303-7207(02)00261-7. 
  12. Sorenmo KU, Goldschmidt M, Shofer F, Ferrocone J (2003). "Immunohistochemical characterization of canine prostatic carcinoma and correlation with castration status and castration time". Vet Comparative Oncology. 1 (1): 48–56. doi:10.1046/j.1476-5829.2003.00007.x. 
  13. Hart BL. (2001). "Effect of gonadectomy on subsequent development of age-related cognitive impairment in dogs". J Am Vet Med Assoc. 219 (1): 51–6. doi:10.2460/javma.2001.219.51. PMID 11439769. 
  14. Lekcharoensuk C, Osborne CA, Lulich JP (2001). "Epidemiologic study of risk factors for lower urinary tract diseases in cats". J. Am. Vet. Med. Assoc. 218 (9): 1429–35. doi:10.2460/javma.2001.218.1429. PMID 11345305. 
  15. Thrusfield MV, Holt PE, Muirhead RH. (1998). "Acquired urinary incontinence in bitches: its incidence and relationship to neutering practices". J Small Anim Pract. 39 (12): 559–566. doi:10.1111/j.1748-5827.1998.tb03709.x. 
  16. Arnold S, Arnold P, Hubler M, Casal M, Rŭsch P (1989). "Urinary incontinence in spayed bitches: prevalence and breed disposition". Europ J of Compan Anim Pract. 131 (5): 259–263. 
  17. Thrusfield Mv (1985). "Association between urinary incontinence and spaying in bitches". Vet Rec. 116: 695. 
  18. Panciera DL (1994). "Hypothyroidism in dogs: 66 cases (1987-1992)". J Amer Vet Med Assoc 204 (5): 761–767. 
  19. Neilson J., Eckstein R., Hart B (1997). "Effects on castration on problem behaviors in male dogs with reference to age and duration of behavior". JAVMA 211 (2): 180–182. 
  20. Jones, Inke; Lucas Ricciardi, Leonard Hall, Hedley Hansen, Vijay Varadan, Chris Bertram, Simon Maddocks, Stefan Enderling, David Saint, Said Al-Sarawi, Derek Abbott (2008-1-17). "Wireless RF communication in biomedical applications" (pdf). Smart Materials and Structures 17: 8–9. IOP Publishing Ltd. doi:10.1088/0964-1726/17/1/015050. Retrieved on 2008-06-25.</cite>  </li>
  21. SpayVac. Retrieved on early 2003. </li>
  22. <cite style="font-style:normal">Gary Killian, Nancy K. Diehl, Lowell Miller, Jack Rhyan, David Thain (2007). "Long-term Efficacy of Three Contraceptive Approaches for Population Control of Wild Horses". Cattlemen's Update: 48–63.</cite>  </li>
  23. DeNicola, Anthony; Lowell A. Miller, James P. Gionfriddo, Kathleen A. Fagerstone (2007-3-16). Status of Present Day Infertility Technology. Northeast Association of Fish and Wildlife Agencies. Retrieved on 2007-03-16. </li>
  24. <cite style="font-style:normal">Fried NM, Sinelnikov YD, Pant BB, Roberts WW, Solomon SB (December 2001). "Noninvasive vasectomy using a focused ultrasound clip: thermal measurements and simulations". Biomedical Engineering, IEEE Transactions on 48 (12): 1453–9. doi:10.1109/10.966604. PMID 11759926.</cite>  </li>
  25. What does Jewish law say about neutering male pets? </li>
  26. <cite class="book" style="font-style:normal" >Feinstein, Moshe. Igrot Moshe.</cite>  </li>
  27. CHAI - Why Spay/Neuter is Crucial </li>
  28. Islam Question and Answer - De-clawing a cat so that it won’t do any damage, and neutering/spaying cats </li>
  29. What some religions say about sterilisation. </li>
  30. Spaying/Neutering Information </li></ol>

External linksEdit

es:Castración is:Vönun nl:Castratie zh:絕育

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