The majority of U.S. pets are altered to prevent their ability to reproduce, as well as to keep them from developing a host of associated health issues. These surgical procedures are called ovariohysterectomy, or “spay,” for females, and orchiectomy, or “neuter,” for males. Veterinarians recommend these procedures because they reduce the risk of highly prevalent reproductive cancers and other complications that can shorten a pet’s life span, and most rescue operations require them to decrease pet overpopulation. 

Many studies find that altered pets experience fewer reproductive issues and generally live longer than intact pets, but new research suggests pets who are altered too early can be at risk for other types of cancer or orthopedic problems. Understandably, you may be confused about when to alter your pet, but the Aloha Veterinary Hospital team can recommend the best timing for your furry pal based on the most current research.

What are the benefits of spaying or neutering pets?

Research shows that sterilizing pets has many overall benefits, including:

  • Greatly reducing the risk for often fatal mammary tumors
  • Eliminating risk for testicular tumors
  • Preventing undesirable behaviors and vaginal bleeding during heat cycles
  • Reducing male pets’ desire to roam, urine mark, or compete for female attention
  • Reducing pet overpopulation and shelter euthanasia
  • Reducing risk for uterine infection, which is a life-threatening emergency

What are the current recommendations for dogs and cats?

Some pets may be at increased risk for certain health problems when surgery is performed too early or too late, but study evidence has been limited and, in some cases, conflicting. In response to this uncertainty, the American Animal Hospital Association (AAHA) has published new guidelines to help veterinarians and pet owners sort through the confusion and better understand the best age to sterilize their pets. The guidelines provide a starting point for veterinarians to determine which pets require early spay or neuter and which might benefit from a later surgery, depending on breed, age, and expected adult size. The current recommendations are as follows:

  • Cats — Spay or neuter is recommended around 5 to 6 months of age, before cats have their first heat cycle or reach sexual maturity. This avoids the significant behavioral changes seen in intact adult cats, as well as provides the medical benefits discussed above.
  • Small dogs — Dogs expected to reach an adult weight of less than 45 pounds should be spayed or neutered before their first heat cycle, which can occur as early as 4 months in some breeds but usually occurs at 6 to 7 months. This recommendation has not changed because research shows small breeds are less affected by hormone-related conditions than larger breeds.
  • Large dogs — For dogs expected to grow to greater than 45 pounds, recommendations vary between males and females. Males should be neutered once they reach their adult size—any time between 9 and 15 months depending on the breed—but the recommendation for females varies from 5 to 15 months depending on several factors we will discuss below.

Spay and neuter timing in large-breed dogs

The recommendation to spay and neuter large breeds later than small breeds is based on several studies of problems that are more prevalent in large and giant breeds. These dogs may have lower risks for the following diseases when they are allowed to reach their full adult size before removing the influence of hormones:

  • Orthopedic problems — Hip dysplasia, knee ligament injuries
  • Certain cancers — Anal gland carcinoma, prostate cancer, osteosarcoma, hemangiosarcoma, transitional cell carcinoma, and mast cell tumors
  • Urinary incontinence — Most common in spayed female dogs, influenced by estrogen

Because male dog reproductive cancers are often less aggressive and more easily treated than female reproductive cancers and because risk for these cancers does not depend on a hormonal heat cycle, allowing males to reach their full adult size before neutering carries little additional risk and may provide benefits over early surgery. The risks for waiting are higher for females, because most will go through at least one heat cycle before they reach their adult size. The incidence for mammary tumors in females who go through one heat cycle is 8% and shoots up to 26% for those who go through two. While late spaying can reduce the risk for other cancers, it’s important to recognize that these cancers are far less common than mammary tumors, and their incidence also may vary by breed.

Benefits must be carefully weighed against risks for female dogs, and more research is needed to determine how breed influences these risks. For many people, the 8% risk for mammary tumors is unacceptable, and they may choose to spay before their pet’s first heat cycle. For others, the risks for orthopedic problems, certain cancers, and urinary incontinence may outweigh the increased risk for mammary tumors, and they choose to wait until a later age. The decision is personal, and should be carefully considered in collaboration with your veterinarian.

Your Aloha Veterinary Hospital veterinarian is the best resource you have in determining the best age to spay or neuter your pet. We base our recommendations on published evidence, professional experience, and individual factors relating to your specific pet to help you make the best decision.