Neutering, from the Latinneuter (of neither sex), is the removal of an animal's reproductive organ, either all of it or a considerably large part. The term is often used in reference to males whereas spaying is often reserved for females. Colloquially, both terms are often referred to as fixing. While technically called castration for males, in male horses, the process is referred to as gelding.
There is some weak evidence that spaying reduces the risk of mammary tumor considerably in female dogs when done before 2.5 years, and even more so if done before the first estrous cycle. It is a very common disorder of female dogs, with a reported incidence of 3.4%. Of female dogs with mammary tumors, 50.9% have malignant tumors. Spaying female dogs more than two years before the removal of mammary tumors increases the dog's survival odds by 45%.
Without the ability to reproduce, a female necessarily has zero risk of pregnancy complications, such as spotting and false pregnancy, the latter of which can occur in more than 50% of unspayed female dogs.
As with any surgical procedure, immediate complications of neutering include the usual anesthetic and surgical complications, such as bleeding, infection, and death. 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. 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 neutering cats may increase the risk of obesity. 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 between 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 neutered dogs as compared to intact males.
Spaying and neutering 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 spayed and neutered dogs had a higher incidence of cranial cruciate ligament (CCL) rupture, a form of anterior cruciate ligament (ACL) injury.
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.
There is some weak evidence that spaying can increase the risk of urinary incontinence in dogs, especially when done before the age of three months. Up till 12 months of age, the risk decreases as the age at spaying increases.
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 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 undesirable sexual behaviors[clarify].
In female animals, spaying involves abdominal surgery to remove the ovaries and uterus (hystero-oophorectomy). Another option is to remove only the ovaries (oophorectomy), which is mainly done in cats and young dogs, and yet 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 & 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, as a method of birth control or for other reasons. In mares, these other reasons include behavior modification.
Traditional open surgery is usually performed through a ventral midline incision below the 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 3 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.
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 their back. The incisions are between 5mm and 10mm and the number varies according 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 inserted. The abdomen is inflated with carbon dioxide gas to create a space to operate in. 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.
The benefits of laparoscopic surgery are less pain, faster recovery, 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, which is a natural calming hormone and a serotonin uplifter. Spaying may therefore escalate any observable aggressive behaviour, either to humans or other dogs.
The risk of infections, bleeding, ruptures, inflammation and even reactions to the drugs given to the animal as part of the procedure are all possibilities that should be considered.
In male animals, castration involves the removal of the testes, 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).
Male animals – Injecting a solution of calcium chloride dihydrate (20% by weight of CaCl2 dissolved in ethanol – 95% ABV) into the testes of the animal results in nonsurgical castration. Within one month, necrosis of the testicular tissue causes sterilization.
Male dogs – Neutersol (Zinc gluconate neutralized by arginine). Cytotoxic; produces irreversible infertility by chemical disruption of the testicle. It is now produced as Esterilsol in Mexico.
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. Using a piezoelectricpolymer 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, 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). 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 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.
Vasectomy: The cutting and tying of the vasa deferentia. 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 people who seek minimal infringement on the natural state of companion animals to achieve the desired reduction of unwanted births of cats and dogs.
Penile translocation is sometimes performed[how?] in cattle to produce a "teaser bull", who retains his full libido, but is incapable of intromission. This is done to identify estrous cows without the risk of transmitting venereal diseases.
Early-age neutering (also known as pediatric spaying or prepubertal gonadectomy – 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%. 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 his/her best knowledge when making the decision about the age at neutering.
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 to 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. Female dogs neutered early are much more likely to develop cystitis although the risk does not appear to be chronic. Two studies showed an increased risk of canine parvovirus infection, which one of the study attributed to the increased susceptibility of young dogs rather than long term immune suppression.
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, 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.
While there are 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 SephardicChief 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.
AB 1634 – A California bill proposing mandatory spay-neuter laws.
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