The AVMA recommends with regards to spaying/neutering “pets should be considered individually, with the understanding that for these pets, population control is a less important concern than is health of each animal.” However, it has been my experience that few veterinarians are evaluating animals as individuals when considering a spay/neuter surgery.
Ovariohysterectomy is a surgical procedure where the uterus and ovaries are removed from the body and orchietomy consists of surgically removing the testes. The sexual organs have functions that impact the whole of the animal, not just the capability to reproduce. In reviewing a multitude of studies on the subject it becomes obvious that there are numerous negative consequences observed in spayed/neutered companion animals.
We know that the sex hormones play a role in promoting closure of the growth plates at puberty and are critical for achieving peak bone density. It is well documented that when spaying/neutering is performed before puberty dogs growth plates will be delayed in closing resulting in longer limbs, lighter bone structure, and narrow chests and skulls. The resulting abnormal growth and body proportions have been implicated in an increased incidence of cruciate ligament tears and hip dysplasia. The prevalence of cruciate ligament rupture was 3.48% in a review of 3218 dogs’ records at one veterinary clinic from a 2-year period. Spayed/neutered dogs had a significantly higher prevalence than intact dogs. One study showed that dogs that were neutered at 6 months were 1.5 times as likely to develop chronic hip dysplasia, compared with intact dogs. Spayed/neutered dogs were found to have a 3.1 fold higher risk of patellar luxation than intact dogs.
Cancer is currently the number one disease related killer of dogs. Studies have shown a higher rate of some types of cancer in spayed/neutered dogs. Spayed females have a 5 times greater risk of developing hemangiosarcoma (one of the three most common types of cancers in dogs) and neutered males have a 2.4 times greater risk than their intact counterparts. Dogs of both genders had a doubled risk of developing bone cancer if they were spayed/neutered before one year of age. A study done on Rottweiller’s reported that dog’s spayed/neutered before one year of age had a 25% chance to develop bone cancer in their life. Both hemangiosarcoma and osteosarcoma (bone cancer) have a very poor prognosis. Spayed/neutered dogs have double the risk to develop urinary tract cancers. The likelihood of a female dog or cat developing mammary cancer is common with a reported incidence of 3.4% and 2.5%. In dogs that are spayed before the first estrus, the statistics show a 0.50% risk, if spayed after 1 estrus cycle the risk rises to 8% and is reported to be 26% in intact females. Approximately 50% of mammary tumors are malignant in dogs. However, when caught early the prognosis is quite good. Intact dogs and cats have a seven times greater risk of mammary cancer their spayed counterparts. Nearly 90% of mammary tumors in cats are malignant.
It is commonly believed that neutering a male dog will prevent prostate cancer. A study on this subject at the College of Veterinary Medicine at Michigan State University concluded that “castration at any age showed no sparing effect on the risk of development of prostate cancer in the dog”. Two other studies, one from America and another from Europe found that neutered dogs have a four times higher risk of prostate cancer that intact dogs. Neutering does however eliminate the risk of testicular cancer completely, which occurs at a rate of about 7% in dogs and even less in cats. Testicular cancer has a low rate of metastasis and is an uncommon cause of death in both intact cats and dogs.
Ovarian hormones are critical for maintaining genital tissue structure and contractility. As such, spayed female dogs are at much higher risk of developing urinary incontinence. This is such a common occurrence that there is now a term for this condition: spay incontinence. It occurs in as many as 20% of spayed dogs. Intact females have a reported 0.3% chance of development. Neutered males have an increased chance of developing urethral sphincter incontinence. Females are also at an increased risk of recessed vulva, vaginal dermatitis and vaginitis, especially when spayed before puberty. Recurring urinary tract infections are 3-4 times more likely in spayed females. Although urinary incontinence does not appear to have any long-term effects on health it is not an insignificant problem. Uncontrolled elimination is likely to get a dog banished to the outdoors or contribute to the decision to relinquish the animal to a shelter. A study of 4,111 cats concluded that spaying/neutering was a risk for the development of feline urological syndrome.
Pyometra is a disorder of the uterus in intact female dogs and cats. Incidence in intact dogs is high at approximately 24% by 10 years of age. It is relatively uncommon in cats.
A study with Golden Retrievers found that the development of hypothyroidism occurred at three times higher rates in spayed/neutered dogs and another study noted spaying/neutering to be the most significant risk factor for the development of this disease.
The high prevalence of aberrant adrenocortical disease and hyperadrenocorticism in pet ferrets in the North America is associated with the practice of spaying and neutering at an early age. Early spay/neuter is known to be associated with increased luteinizing hormone (LH) and follicle stimulating hormone (FSH) in ferrets and other species. LH and FSH concentrations in spayed and neutered dogs are 10-fold above those of intact animals. Early spay/neuter plays a part in the adrenal glands ramping up their production of hormones. This additional production of hormones from the adrenal glands is a likely contributor to the development of atypical cushings disease in dogs.
When animals are spayed/neutered before puberty the endocrine, glandular and hormonal systems are not yet fully developed. The adrenal glands are the only other source for production of the sex hormones progesterone, estrogen and testosterone. Estrogen is needed to promote closure of the growth plates. Dogs that are spayed/neutered at early ages have delays in the closure of their growth plates. A study done on 32 mixed breed dogs showed that those neutered at both 7 weeks of age and seven months of age growth plate closure was delayed compared with intact dogs.
Both genders are at increased risk for obesity once spayed/neutered. The risk factor is tripled in males and doubled in females. An animal’s metabolic rate will drop after sterilization surgery. In other words they will need to consume less calories to maintain their weight. If they are free fed and are sedentary it only stands to reason that weight gain will occur. Whereas if food intake is regulated and exercise is provided weight gain will not occur. Cats also have an increased risk in developing diabetes after spaying/neutering.
The Canine Health Foundation reported a higher incidence of adverse vaccine reactions in neutered dogs. A large-scale study by the AVMA reported a 27 – 38% greater risk of adverse vaccine reactions in spayed/neutered dogs versus intact dogs. A cohort study of shelter dogs concluded that infectious diseases were more common in dogs that were sterilized at less than 24 weeks of age. This indicates that spaying/neutering has an effect on the immune system.
Within all the findings of studies on the prevalence of these health conditions it is worth mentioning that different breeds can show a higher or lower predisposition to certain conditions.
Physical health is not the only aspect that is affected by the removal of the reproductive organs. Studies have shown that there are also behavior differences. The most common problem reported in spayed female dogs was fearful behavior and in neutered males the most common problem was aggression, with the exception of inter male aggression, which was reduced. Early age spay/neuter results in increased incidence of noise phobias and mounting behavior in dogs. Neutered male dogs show an increased risk for progressive geriatric cognitive impairment. In male cats neutered at an early age there was an increase in hiding behavior and shyness around strangers.
There are few health benefits to surgically removing the reproductive organs, especially at young ages. Most obviously the testes, uterus and ovaries cannot become cancerous, if they have been removed. However, there is a very low incidence of these types of cancers in dogs.
So what is the pet owner to do? How can pregnancies be prevented without creating a negative impact on our animal’s health and behavior?
The first and most obvious choice is to leave our pets with all the body parts they were born with. If you have a female pet then keeping her away from any intact males for several weeks is quite manageable. It does become more complicated if you have both male and female intact pets of the same species in your home. Keeping animals securely separated during estrus is essential to prevent unwanted pregnancies. You may consider having a friend look after either the male or female during this time. Animals may become somewhat difficult to deal with as their instinct to mate can cause their usual good behavior to suddenly disappear!
Our pets are born with reproductive organs and they are also meant to mate and propagate their species. Leaving animals intact yet preventing them from breeding has its own issues. The drive to mate can cause mental stress when the animal is prevented from mating. In dogs, the prostate functions best when it is regularly activated from mating. Intact male dogs that are not allowed to breed have an increased likelihood to develop prostate problems. Female ferrets remain in estrus until they are bred. If they are not bred they can die from aplastic anemia. I suspect that there are additional negative health consequences in intact animals that are prevented from breeding. In human women there are increased risks for ovarian cancer and breast cancer for women who have never had children. The same risks could be present in different animal species.
For females consider a laparoscopic spay as it is less invasive and has a faster recovery time. In this procedure the organs are removed through a very small incision. This results in less trauma and pain for the patient, and fewer complications. However the pet owner will pay more for this procedure compared to a traditional spay.
Besides the traditional spay/neuter procedure animals can reap many benefits from organ sparing procedures commonly done on humans known as a vasectomy (males) and a tubal ligation (females). These procedures have the same goal of preventing pregnancy in both humans and animals while leaving the reproductive organs in the body. Unfortunately these procedures have not yet become mainstream and pet owners may have some difficulty locating a vet who is willing to do the procedure. However, don’t hesitate to discuss this option with your vet. Only when there is an obvious demand for this procedure will more vets start offering it.
Vasectomies and tubal ligations would be excellent options for animal shelters to use on young animals prior to adoption. Although this procedure will remove the ability to conceive it does not halt estrus or diminish the instinct to mate. The organs are still present to deliver the hormones to other parts of the body to promote good health. A traditional spay/neuter procedure can always be performed after the animal has reached maturity.
With domestication comes a compromise between the animal’s natural lifestyle and a lifestyle adapted to living in human society. If we continue to keep animals we are going to have to reconcile to the fact that our choices have very real effects on their health and well being. In my opinion a responsible and ethical pet owner needs to be aware of the consequences of their choices and place the animal’s health ahead of their own convenience.
It is wise to keep in mind that any scientific studies with animals are likely using animals that are not living a health promoting lifestyle in the first place. So the prevalence of cancer and other diseases could generally be minimized by a healthier lifestyle and optimal nutrition no matter what decision we make about our pets reproductive organs.