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Key Points
  • Timing of sexual maturity varies depending on the breed and size of your dog.
  • Puppies may be fertile before you realize it, so take steps to prevent unwanted breeding.
  • Research shows that too early spay/neuter procedures may affect long-term health.
National Sibling Day

Humans take years to develop. Dogs though, in our eyes, mature almost overnight. One morning you have an adorable little puppy on your hands, and the next your puppy is starting to act like a teenager, complete with mood swings and behavioral changes. Sexual maturity is an important part of this process, and it is something that we need to understand if we want to be responsible dog owners. Here is what you need to know about sexual maturity to keep your puppy healthy and prevent unwanted breedings.

When Do Puppies Reach Sexual Maturity?

The timing of sexual maturity is largely size- and breed-dependent. So, talk to your vet and breeder about your puppy. Sexual maturity in puppies typically begins to occur between 6-to-9 months of age, although certain giant breeds may not reach sexual maturity until they are older.

However, most dogs are at least 9-to-11 months old before their growth plates close. This also varies based on size and breed. Many veterinarians believe it can be harmful to spay or neuter your dog before the growth plates close. The reason is that such procedures can alter hormones, which are critical to proper bone growth.

What To Expect As Your Puppy Sexually Matures

We all know what happens to humans when we hit puberty. Dogs get to skip the acne and facial hair, but they do experience significant hormonal changes that can alter behavior. The changes are different for male and female puppies.

Sexually mature female dogs typically go into heat twice a year. The most noticeable change during this time occurs at the start of their heat, called proestrus. The bitch’s vulva will swell, and she will lick the area and urinate more frequently. She will also develop a red vaginal discharge for a period of 7-to-10 days, a bit like a human period. The female dog can be fertile for as long as 2-3 weeks.

Two Tibetan Spaniel puppies playing in the grass.

The first heat usually takes place when the pup is between 6 and 15 months, depending on the breed and size of the dog. It’s important to understand that a puppy can become pregnant during her first heat, so be sure to keep a close eye on her if you decide not to spay yet, and keep her on a leash when you take her outside.

Male dogs are sexually active year-round and can be capable of siring puppies when they’re as young as 5 months, but they are most fertile after 12-to-15 months of age, once they are fully physically mature. At this stage, they have higher testosterone levels than even adult male dogs have, which may cause other male dogs to be aggressive toward them.

Males can start to mark their territory as they become sexually mature, which many owners consider an undesirable trait. Roaming is another behavior that is sometimes characteristic of sexually mature male and female dogs.

Providing your adolescent dog with physical and mental exercise and continuing your puppy training will help you to prevent or mitigate behaviors that develop at that age. Try to be patient. Remember that this is just a phase that will come to an end as your dog grows. It helps to reinforce the behaviors you want and discourage the ones you don’t want.

Spaying & Neutering

The most important decision you need to make as your puppy reaches sexual maturity involves spaying and neutering. Unless you plan on breeding or showing your dog, many veterinarians recommend spaying and neutering.

Timing is an important consideration, in addition to whether or not to spay or neuter at all. Allowing a female pup to have one heat cycle helps to be sure she is mature and finished growing. When a puppy is spayed or neutered before reaching full maturity, there may be a risk of future orthopedic problems. In puppies, hormones instruct the growth plates when to close. Spaying before puberty causes the growth plates, which are still open, to remain open longer. This can make the dog or bitch orthopedically out of balance.

AKC Canine Health Foundation-funded research has led to the following conclusion: “Most dogs in the United States are spayed or neutered, and for years the procedures have been completed prior to maturity. The research suggests that veterinarians should be more cautious about the age at which they spay and neuter in order to protect the overall health of dogs.”

Research results have shown that early spay or neuter (before the age of 12 months) can impact the incidence of different types of cancer, hip dysplasia, and development of canine cruciate ligament ruptures.

In an article entitled “Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs,” author Laura J. Sanborn, M.S. says: “An objective reading of the veterinary medical literature reveals a complex situation with respect to the long-term health risks and benefits associated with spay/neuter in dogs. The evidence shows that spay/neuter correlates with both positive and adverse health effects in dogs. It also suggests how much we really do not yet understand about this subject.”

“The decision of when and whether to spay or neuter a dog isn’t one to be taken lightly,” says Dr. Jerry Klein, AKC chief veterinarian officer. “The AKC believes that these important decisions should be made on an individual basis by the owner of the dog in conjunction with his or her veterinarian.”

Dog Breeding

Breeding a male or female dog to produce healthy puppies that contribute to the welfare of the breed, and are desired by responsible owners, takes a great deal of knowledge, research, and planning. It is best to work with an experienced mentor, a reputable breed club, and a veterinarian.

Sexual maturity in puppies can happen before your puppy is fully grown, which can be dangerous for females. Therefore, the AKC recommends waiting until after your female’s first heat to breed her. If you decide you do want to breed your puppy after maturation, make sure you do your research, as this decision comes with a lot of responsibility.

Understanding when sexual maturity in puppies takes place, and what it means for your dog, will help you become a more responsible dog owner. This knowledge allows you to make better decisions regarding your dog’s health. And knowing the science behind sexual maturity in puppies will help you understand your puppy’s changing and sometimes confusing behavior.

Need help with your adorable new puppy? Training your dog can be challenging without expert help. That’s why we’re here to help you virtually, through AKC GoodDog! Helpline. This live telephone service connects you with a professional trainer who will offer unlimited, individualized advice on everything from house-training to behavioral issues.

This article is intended solely as general guidance, and does not constitute health or other professional advice. Individual situations and applicable laws vary by jurisdiction, and you are encouraged to obtain appropriate advice from qualified professionals in the applicable jurisdictions. We make no representations or warranties concerning any course of action taken by any person following or otherwise using the information offered or provided in this article, including any such information associated with and provided in connection with third-party products, and we will not be liable for any direct, indirect, consequential, special, exemplary or other damages that may result, including but not limited to economic loss, injury, illness or death.
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