The question of when to spay a female dog is one that many owners ask. A recent scoping review published in PLOS One set out to find answers by looking at how spaying before or after puberty affects health outcomes. The review examined 33 studies, but only six considered whether the dogs had reached puberty. The rest looked at age instead of true pubertal status. This makes it hard to draw solid conclusions about the best time to spay a dog relative to puberty.
A scoping review provides a broad overview of the studies on a topic, identifying key concepts, research gaps, and different types of evidence.
What the studies found — and what they missed
The review found no clear evidence that spaying before or after puberty affected conditions like allergies, developmental orthopedic disease, or obesity. Some studies looked at urogenital health, but their results were inconsistent. Breed differences and study design issues also made it tough to compare the studies.
Puberty is defined as sexual maturity, or when reproduction becomes possible. Certain behavioral signs mark the onset of puberty in dogs, such as the first heat cycle in females and mating behavior in males, but they may be difficult to observe. The more important factor for dog health and well-being is hormonal maturity, which can be measured by endocrine assays. These are not routinely conducted, so while the review focused on puberty, most dog owners and veterinarians only know a dog’s age. Thus, it’s not surprising that the review did not find enough previous studies with puberty assessments to make conclusions about the optimum timing of sterilization.
A different perspective: keeping hormones matters
For the last 15 years, evidence for the relationship between the loss of natural hormones resulting from spay and neuter and health or behavior problems has been mounting. Today, a host of studies have shown that neutered dogs have a higher risk of cancer, orthopedic issues, incontinence, obesity, immune diseases, and behavior issues like aggression and fearfulness. The risk can depend on issues like the size, breed, age, and sex of the individual dog. Delaying spay or neuter can help reduce the risk. Drs. Benjamin and Lynette Hart from the University of California, Davis have published findings about the suggested spay/neuter ages for 40 popular breeds.
The importance of hormones for lifelong canine health goes even further. That’s where Dr. Chris Zink’s research comes in. In a 2023 study, Dr. Zink and colleagues reported that dogs with longer exposure to their natural hormones had fewer health and behavior problems. They lived longer and showed better health outcomes overall. This occurred whether they remained intact longer, or had a hormone-preserving sterilization method instead of standard spay or neuter surgery.
“The bottom line is that the longer dogs have their natural hormones, the healthier they are,” Linda Brent, executive director of the Parsemus Foundation, said. “There’s a simple solution to preventing unwanted puppies while maintaining health. It’s called hormone-sparing sterilization, and it’s a good option for many dogs.”
What this means for dog owners
Spaying and neutering doesn’t just prevent reproduction; it eliminates hormones that play a role in keeping dogs healthy. Hormone-sparing sterilization options, like vasectomy or hysterectomy (ovary-sparing spay), give dogs the benefits of natural hormones while preventing unwanted litters. These procedures can be performed at any time, because the sex hormones that stimulate puberty will not be affected and the dog will have normal, balanced hormone levels throughout life — and will not be able to reproduce. If you haven’t heard of it yet, learn about hormone-sparing sterilization here.
Moving forward: more research — and more options
The scoping review concluded that more research is needed to understand the effect of spaying on health, especially in relation to puberty. While that’s true, we shouldn’t overlook the wealth of data already available. Early or traditional spay and neuter surgeries remove the ovaries or testicles, which are essential for hormone production. That’s why many health problems appear after these surgeries.
Additional long-term studies are needed to fully understand how disruption of the hormones after spay and neuter affects diverse parts of the body (“spay-neuter syndrome”). Some research implicates the extremely high levels of luteinizing hormone resulting from the loss of sex hormones. And research is just beginning to show the promise of hormone restoration for dogs that have already undergone spay/neuter.
Our recommendation
At the Parsemus Foundation, we believe that pet owners deserve clear information and should understand the options available for pet healthcare. Studies like Dr. Zink’s show that preserving hormones helps keep dogs healthier and happier. We recommend that pet owners consider hormone-sparing sterilization before making a decision to spay or neuter their dogs. Talk to your veterinarian about these options, or use our Veterinarian Directory to find a clinic that offers them. They can help you make the best choice for your dog’s health and well-being.
See our other blog posts on hormone-sparing sterilization for pets.
