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Disadvantages
General
- 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 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.[8]
- 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.[9] In cats, a decrease in sex hormone levels seems to be associated with an increase in food intake.[10] In dogs, the effects of neutering as a risk factor for obesity vary between breeds.[11]
- 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.[12][13][14]
- 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.[15][16]
- Spaying and castrating is associated with an increase in urinary tract cancers in dogs, however the risk is still less than 1%.[17]
- 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%.[18]
- Neutered dogs have also been known to develop hormone-responsive alopecia (hair loss).[19]
- 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.[20]
- A study of golden retrievers found that castrated males were 3 times more likely than intact males to be diagnosed with lymphoma and 2 times more likely to have hip dysplasia.[21]
Specific to males
- About 2% of castrated male dogs eventually develop prostate cancer, compared to less than 0.6% of intact males.[22][23] The evidence is most conclusive for Bouviers.[17]
- 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.[24]
- As compared to intact males, castrated cats are at an increased risk for certain problems associated with feline lower urinary tract disease, including the presence of stones or a plug in the urethra and urethral blockage.[25]
- Neutering also has been associated with an increased likelihood of urethral sphincter incontinence in male dogs.[26]
Specific to females
Further information:
Canine reproduction § Altered Females
- 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.[27]
- Spayed female dogs are at an increased risk of hypothyroidism.[28]
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
other factors have more of an effect than neutering.
[29][30] One study reported results of aggression towards familiar and strange people and other dogs reduced between 10 and 60 percent of cases,
[31] while other studies reported increases in possessive aggression
[32] and aggression towards familiar and strange people,
[33] and more studies reported there was no significant difference in aggression risk between neutered and non-neutered males.
[30][34] For females with existing aggression, many studies reported increases in aggressive behavior
[35][36][37][38] and some found increased separation anxiety behavior.
[33][39] 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.
[40] Early age gonadectomy is associated with an increased incidence of noise phobias and undesirable sexual behaviors[
clarify].
[41]
https://en.wikipedia.org/wiki/Neutering
