The Latest on When to Spay or Neuter Your Pet

When do you spay or neuter a dog or cat? For years, you’ve probably heard that the best age for this reproductive surgery is six months, but times change. Veterinarians and pet owners are taking a closer look at when it should occur. And the answer isn’t what you might think.

For kittens, the answer is easy: the earlier the better. As soon as they are five months old or weigh one and a half pounds, tiny as that might seem, they can be surgically altered. That’s important, because kittens reach reproductive age very early in life, sometimes even before they are five months old.

In a time when kittens are the most vulnerable animals in shelters because of the difficulty of caring for them until they’re old enough for adoption, reducing the overwhelming number of kittens is job one. For them, early spay/neuter surgery is safe and timely. Surgery takes less time, kittens are anesthetized for a shorter period, and they recover rapidly.

Dogs, however, are another story. Because of their wide variability in size and developmental maturity, as well as documented links between certain diseases and age at which they are spayed or neutered, it’s much more important to determine the optimal age. And rarely is it as early as six months. (The exception is puppies adopted from shelters, where they are often spayed or neutered before adoption.)

Why? Sex hormones are important for appropriate closure of the growth plates. Puppies altered early tend to grow taller. That may be why dogs who are spayed or neutered at an early age have significantly higher incidences of ruptured cranial cruciate ligaments, among the most common injuries in dogs. That’s according to sports medicine veterinarian Chris Zink, DVM, who has studied a slew of research papers on the effects of the surgery based on age.

Other studies show that the age at which a dog is spayed or neutered can affect behavior, growth, development of orthopedic problems, and occurrence of certain types of cancer. In general, the larger the dog will be at maturity, the better it is to spay or neuter them after growth ends.

Does that mean you shouldn’t spay or neuter your dog? Absolutely not! There are many good reasons to do so, including prevention of unwanted pregnancies and decreased roaming or escape attempts to find a mate and make puppies. It does mean that you and your veterinarian should discuss factors such as your home environment, the dog’s lifestyle, and the breed’s potential risk of certain diseases or injuries in deciding the appropriate age for the surgery to take place.

For instance, Dalmatians are susceptible to urate stone formation, which can cause painful and even fatal urinary blockages. In that breed, it’s recommended that males not be neutered before they are a year old, so their urinary systems have time to fully develop.

In Golden Retrievers, published studies by Benjamin L. Hart, DVM, and Lynette Hart, Ph.D., at the School of Veterinary Medicine, University of California, Davis, have shown a significant increase in one or more joint disorders when the dogs were altered at six months of age. Their figures were confirmed in a second study by the Morris Animal Foundation, using a different database and study design. And in females of any breed, early spay surgery can contribute to urinary incontinence and recurring urinary tract infections.

Because there are so many variables, there are no hard and fast recommendations. A good baseline is to wait until 12 to 14 months of age, when growth plates have closed.

There are advantages and disadvantages to altering dogs or keeping them intact–at least for a time–and many depend on breed or expected lifestyle. To make the right decision for you and your dog, have a conversation with your veterinarian about individual risk factors.

This article was reviewed/edited by board-certified veterinary behaviorist Dr. Kenneth Martin and/or veterinary technician specialist in behavior Debbie Martin, LVT.

Kim Campbell Thornton is content manager for Fear Free Pets and is a Level 3 Fear Free Certified Professional. She has been writing about dogs, cats, wildlife, and marine life since 1985 and is a recipient of multiple awards from the Cat Writers Association, Dog Writers Association of America, and American Society of Journalists and Authors. When she’s not writing or editing, she’s competing in nose work trials with Harper and Keeper, her Cavalier King Charles Spaniels.