Do we need a paradigm shift in canine neutering?
Sources: dvm360, Frontiers in Veterinary Medicine
The history of spay and neuter
In the 19th century, urbanization and increased pet ownership were catalysts for performing neuters. Owners found a pet’s heat cycle in their home to be inconvenient, so neuters were performed to eliminate this annoyance. In the 1950s, neutering became the solution to overpopulation of pets in New York City. By the 1960s, when compliance to neuter contracts was low, humane groups made neutering a requirement prior to pet adoption. In 1975, the Maryland Society for the Prevention of Cruelty to Animals recommended early neuter to get as many pets neutered before adoption as possible. Then in 1993, the American Veterinary Medical Association supported early neuter for the purpose of curbing overpopulation.
A standard of practice
Neutering young dogs between 6 and 9 months of age is now common practice. This practice in the US contrasts with many European countries, where neutering is quite uncommon. For example, in Norway, it’s illegal to neuter a pet unless there is a valid medical reason. With these opposing philosophies, veterinarians in the US have begun questioning the validity of the juvenile neuter approach. Practitioners are asking: What are the clinical effects of removing these hormones? How early is too early? Are there even benefits to spay and castration?
Spay and neuter benefits
Preventing mammary tumors is a well-known justification for spaying females before their first heat. Every vet student reads the classic paper, which reports only half a percent of female dogs developing mammary tumors if they are spayed prior to their first heat. In contrast, 26% develop tumors if they are spayed after their second heat. Removing these hormones has also been shown to decrease or eliminate the development of reproductive tract tumors and pyometra, which affects nearly 1 in 4 intact females by age 10. It also eliminates other things, such as bleeding in the house and unwanted pregnancies. Additionally, there is evidence that these pets may live longer.
Castration removes the risk of testicular cancer, which affects 27% of intact males. Removing cryptorchid testicles is particularly important, as they have a significantly higher risk of developing tumors. There is also a reduced risk of prostate hyperplasia, perianal tumors, and perineal hernias with castration. There is even indication that castration decreases unwanted behaviors, such as urine marking in the house, roaming (which can lead to injury and reduced lifespan via fights and getting hit by cars), and mounting.
Unintended consequences
Spay and castration have a handful of negative effects worth noting. To start, it is a surgical procedure, which carries an inherent 6% risk of complications, including incisional infections and anesthetic events.
Urinary Incontinence
It also increases the risk of urinary incontinence in females. Fewer than 1% of intact females develop incontinence, but 4% to 20% of spayed females are at risk. This risk goes up when spayed before 3 months of age.
Another concern is leaving a pet with immature genitalia. Immature, recessed vulvas can lead to urinary tract infections and perivulvar dermatitis. Spay and castration have also been reported to increase the risk for hypothyroidism and vaccine reactions. Further, spaying can predispose females to aggression toward family members. There may also be a faster progression of cognitive impairment in neutered pets, especially males. Finally, obesity, which has its own set of risks, is much more common in both spayed and castrated pets.
ACL Injuries
There are also orthopedic considerations for pets neutered at a young age. Early neuter has been shown to delay growth plate closure, resulting in taller pets. By altering bone growth, a pet’s conformation is affected and may predispose them to excessive tibial plateau angles. When the tibial plateau angle is excessive, there is a significantly greater risk of developing cranial cruciate ligament disease in 1 or both knees. Hip dysplasia has also been found to be more common in altered pets, especially when neutered before 6 months of age.
Cancer
In addition to the above medical concerns, there are also various cancers that have been shown to be more prevalent in neutered pets. Mast cell tumors, hemangiosarcoma, lymphoma, and osteosarcoma have been reported to occur more frequently in neutered pets.
A study of Rottweilers found that when spayed prior to 1 year of age, females had nearly 3 times the risk of developing osteosarcoma, and males had almost 4 times the risk. For neutered males, there is also about 4 times the risk of developing prostate cancers.
UC DAVIS Study
A new, 10-year study by researchers at the University of California, Davis, examined 35 dog breeds and found vulnerability from neutering, and the age at which they are neutered, varies greatly depending on the breed.
Some dog breeds have higher risk of developing certain cancers and joint disorders if neutered or spayed within their first year of life. Until now, studies had only assessed that risk in a few breeds. A new, 10-year study by researchers at the University of California, Davis, examined 35 dog breeds and found vulnerability from neutering varies greatly depending on the breed. The study was published in the journal Frontiers in Veterinary Science.
Previous studies have found that neutering or spaying female golden retrievers at any age increases the risk of one or more of the cancers from 5 percent to up to 15 percent.
When to spay and neuter
DISCUSS CHOICES WITH VETERINARIANS
Dog owners in the United States are overwhelmingly choosing to neuter their dogs, in large part to prevent pet overpopulation, euthanasia or reduce shelter intake. In the U.S., surgical neutering is usually carried out by six months of age.
This study suggests that dog owners should carefully consider when and if they should have their dog neutered.
"We think it's the decision of the pet owner, in consultation with their veterinarian, not society's expectations that should dictate when to neuter," said Benjamin Hart. "This is a paradigm shift for the most commonly performed operation in veterinary practice."
