It’s Almost Always Best To Spay And Neuter Pets

By far the most common surgeries performed on dogs are spay and neuter procedures — collectively called gonadectomies — that remove the reproductive organs to prevent unwanted pregnancies and pet overpopulation.


Dr. Teri Kidd was the first person to perform a spay and neuter procedure in the University of Illinois shelter medicine mobile surgical unit, acquired with funding from PetSmart Charities.

But while these surgeries are common, they are not without controversy. Misconceptions and concerns about these procedures abound. A big reason for the confusion is the overwhelming number of studies that have been done on gonadectomies. Intuitively, you might think that so much research on a subject would provide ultimate clarification, but instead the ocean of data has caused a lot of uncertainty.


Dr. G. Robert Weedon directs the shelter medicine program at the University of Illinois College of Veterinary Medicine in Urbana, which performs more than 4,000 low-cost spay and neuter surgeries each year at rural shelters in east central Illinois.


He says that many research studies have been misinterpreted or over-interpreted, causing confusion among both veterinarians and owners.

That is why Dr. Weedon and three fellow shelter medicine researchers from the University of Minnesota, the American Society for the Prevention of Cruelty to Animals and Mississippi State University recently published a review article* evaluating the relevant literature and drawing conclusions about gonadectomies, especially regarding the optimal age to perform this procedure.

Here is a sampling of the findings covered in Dr. Weedon’s article. Take care to note the incidence of each disease.

  • Mammary neoplasia (cancer of the mammary glands) is seven times more likely in unspayed female dogs than in those that have been spayed; the incidence of this cancer ranges from 3.4% to 13%. Optimal spay age to avoid mammary neoplasia in female dogs is less than 2.5 years. • Benign prostatic hypertrophy/hyperplasia (a non-cancerous, enlarged prostate) occurs in more than 50% of intact male dogs, with incidence increasing with age.
  • Four out of five studies show an increase in prostate cancer in neutered dogs; however, this cancer arises in only 0.2% to 0.6% of the population.
  • Testicular neoplasia, with an incidence of 0.9%, is only seen in intact male dogs.
  • Pyometra (inflamed or infected uterus) occurs in roughly 25% of intact female dogs.
  • Obesity is very common in spayed and neutered dogs, reported to be between 21.4% and 44.4%.
  • This list, which represents only a fraction of the data Dr. Weedon and his coauthors address in their review, helps illuminate the complexity of the science regarding sterilizing pets. The ideal age for a spay or neuter is not clear cut; veterinarians have to consider many factors when recommending timing for the procedure.


For example, waiting until a later age to spay or neuter a pet may increase the dog’s risk of certain types of cancer. Choosing not to spay or neuter a dog leaves the animal at a relatively high risk of pyometra in female dogs and benign prostatic hypertrophy/hyperplasia in male dogs.

On the other hand, currently published data suggests that in some breeds, spayed and neutered pets have an increased risk of other types of cancer, as well as of obesity.

Your veterinarian is responsible for evaluating the relative risks and communicating those risks accurately to you. For example, you may hear of a study that indicates that that spaying your female dog increases her likelihood of acquiring bladder stones; your veterinarian should discuss this risk with you, and let you know that bladder stones are reported in only one in 100 dogs.

And the connection between the gonadectomy and the disease may be coincidental rather than causal. In the case of bladder stones, Dr. Weedon emphasizes, “no clear cause-and-effect has been established between spays and an increased risk of bladder stones.” Some veterinarians speculate that the increased rate may be due to the fact that owners who have had their dogs spayed are more observant and more willing to seek veterinary care and treatment for bladder stones.


Dr. Weedon recommends spaying or neutering pets in almost every scenario, although the ideal age can change depending on the breed and health of your dog, as well as the circumstances in which the dog lives. Your veterinarian has the knowledge to help interpret the large amount of contradictory data, and the training to make the best recommendation for the age at which to sterilize your pet.

To learn more about the risks and benefits of spay and neuter surgeries for your dog, contact your local veterinarian.

*Root Kustritz MV, Slater MR, Weedon GR, Bushby PA. Determining optimal age for gonadectomy in the dog: A critical review of the literature to guide decision making. Clinical Theriogenology 2017;9(2):167-211.

From the University of Illinois UrbanaChampaign College of Veterinary Medicine

Feline Leukemia Virus


Feline leukemia virus (FeLV) is an agent that spreads easily between cats and has potentially lethal effects, causing a variety of secondary diseases that range from secondary infections to cancer. Dr. Stanley Rubin, a veterinarian who specializes in internal medicine at the University of Illinois Veterinary Teaching Hospital in Urbana, says that FeLV is most common in outdoor male cats between the ages of one and six years old. However, kittens are at the greatest risk of infection because they do not have a fully developed immune system.

“The overall prevalence of FeLV has decreased as cat owners’ awareness of the infection has increased and steps have been taken to control the disease, such as removing cats that are FeLV positive and restricting cats to indoor lifestyles,” Dr. Rubin says. Careful monitoring and the routine use of FeLV vaccines may also be helpful.

FeLV is transmitted between cats by prolonged close contact with saliva and nasal secretions, or by sharing common water or food sources. Sometimes it can be transmitted through bites or from moms to kittens via milk, or before the kittens are born. The virus does not survive long outside a cat’s body, however. Dr. Rubin says there is no risk of cats transmitting FeLV to humans. “Numerous facts suggest that human infection is not possible,” Dr. Rubin assures.

Initially, the virus enters a cat’s bloodstream and starts to multiply. Sometimes the cat’s immune system is strong enough to fight off the infection at this stage. If not, the virus eventually travels to the bone marrow, which is where some of the body’s immune cells are produced. At this point, cats have a harder time fighting off the virus and may have FeLV for the rest of their lives. The infection can cause anemia (low number of red blood cells) and immunosuppression.

“Having a weakened immune system leaves the cat susceptible to secondary infections, also called opportunistic infections,” says Dr. Rubin. “They are more readily affected by bacteria, viruses, fungi and parasites.” As the disease progresses, it may lead to neurologic disorders, kidney failure, arthritis and abortion in pregnant cats. Because FeLV hijacks the cells’ replicating machinery, it is not surprising that this disease can ultimately lead to tumour growth. In fact, FeLV is the most common cause of cancer in cats, with the most common type of cancer being lymphoma. “A cat infected with FeLV may begin showing signs of lethargy, fever, weight loss, loss of appetite and depression,” Dr. Rubin says.

Since these signs could indicate a variety of diseases, veterinarians diagnose FeLV by collecting blood and performing tests to detect the presence of the virus in the cat. Depending on the clinical signs, the patient may be treated with blood transfusions, medications for opportunistic infections,

immunotherapy, chemotherapy or antiviral medications. “Vaccinations are available,” Dr. Rubin says, “but it is important to remember that they do not provide 100% protection against infection.” Vaccines are important in certain geographic locations where FeLV is more prevalent, such as areas that have a high density of roaming cats. Owners should consult their veterinarian to determine if a vaccine is necessary in their location. Preventive measures should also be taken to reduce the risk.

FeLV can be prevented by keeping cats indoors to avoid contact with outdoor cats. Survival times depend on how the infection progresses and manifests itself, the strength of the cat’s immune system and the type (or strain) of FeLV. Some cats are able to completely overcome the infection while others may suffer from recurrent bouts of infection only when their immune systems are suppressed, such as when they are weakened by another sickness.

Still others suffer from a persisting, also called progressive, form of the virus for the rest of their lives. Cats with progressive infections in multicat households can live up to three years with FeLV. However, survival rates increase when affected cats are kept indoors in single cat households with good veterinary care. To learn more about feline leukemia virus, consult your local veterinarian.

University of Illinois College of VeterinaryMedicine