Neutering (spay and neuter)

[eibuddy]

Neutering is the removal of an animal's reproductive organ, either all of it or a considerably large part. It is the most drastic surgical procedure with sterilizing purposes. The process 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.

Unlike in humans, neutering is the most common sterilizing method in animals. In the United States, 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.

Advantages

Besides being a birth control method, neutering[males]/spaying[females] has the following health benefits:

Prevention of mammary tumors: Female cats and dogs are seven times more likely to develop mammary tumors if they are not spayed before their first heat cycle. The risk is generally estimated at 25% over a lifetime in unspayed females, meaning that the risk is reduced to ca. 3.6% over a lifetime in females spayed before their first heat.
Pyometra is prevented, either due to the removal of the organ (when ovariohysterectomy is performed) and/or because of the lack of female sex hormones (oestrogen and progesterone) after spaying.
Uterine cancer, ovarian cancer and testicular cancer are prevented due to the removal of the susceptible organs. These cancers are uncommon in dogs and cats, with only a 1% risk of obtaining testicular or ovarian cancer. In female rabbits, however, the rate of uterine cancer may be as high as 80%.

Disadvantages

A cat under anesthesiaAs 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. 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 risk for sick dogs and cats were 1.33% and 1.40% respectively.
Neutered dogs and cats of both genders have an increased risk of obesity. Theories for this include reduced metabolism, reduced activity, and eating more due to altered feeding behavior.
Neutered dogs of both genders are at a twofold excess risk to develop osteosarcoma as compared to intact dogs, as well as an increased risk of hemangiosarcoma and urinary tract cancer.
Neutered dogs of both genders have a 27% to 38% increased risk of adverse reactions to vaccinations. The incidence of adverse reactions for neutered and intact dogs combined is 0.32%
Neutered dogs have also been known to develop hormone-responsive alopecia (hair loss).

Specific to Males

Neutered male dogs display a fourfold increased incidence of prostate cancer over intact males.
In a study of 29 intact male dogs and 47 castrated males aged 11–14, the neutered males were significantly more likely to progress from one geriatric cognitive impairment condition (out of the four conditions - disorientation in the house or outdoors, changes in social interactions with human family members, loss of house training, and changes in the sleep-wake cycle) to two or more conditions. Testosterone in intact males is thought to slow the progression of cognitive impairment, at least in dogs that already have mild impairment.
As compared to intact males, male neutered 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.

Specific to Females

Spayed female dogs can develop urinary incontinence. Studies report incidence rates of 4.9% to 20%.
Spayed female dogs are at an increased risk of hypothyroidism
Despite the risk of pyometra being greatly reduced in spayed females, Stump pyometra may still occur in this group.