Dog reproduction: Facts & myths

Pregnant dog lays in bed preparing for whelping

According to the ASPCA, over two million dogs are adopted from animal shelters across the USA each year. There are currently 32 states with mandatory spay or neuter requirements for pets adopted from animal shelters or rescue organizations. If you are one of these pet owners, chances are you’ve never had to deal with the realities of caring for an “intact” male or female dog. But if it’s your first time adopting, buying, or taking in a dog or puppy that has not been spayed or neutered, you may be wondering what to expect from the natural canine reproduction cycle.  

As with any complex issue, myths around dog reproduction abound. It’s important to have clear facts in order to make an informed decision on whether to spay or neuter your dog. Let’s jump in with the first fact: spaying refers to the process of removing a female dog’s ovaries; while neutering is the process of removing the testes from the male dog. Spaying eliminates the female dog’s natural heat cycle and both procedures will prevent breeding instinct-related behavior.  

If you decide to keep your dog intact for breeding or other purposes, it’s important to be well-informed in order to ensure your dog stays safe and happy. Let’s take a look at some of the common myths and important facts surrounding dog reproduction.  


I don’t need to worry about reproduction until my dog is a year old 

Unfortunately, you can’t just sit back and relax about reproduction during your puppy’s first year. Most dogs reach sexual maturity at six months, though smaller breeds can begin as early as four months. If you have a large breed dog, such as a great Dane, it takes as many as two years for them to reach reproductive maturity. 

In female dogs, this means they start their first estrus or “heat” cycle. Male dogs do not go through a fertility cycle, instead, they respond to pheromones released by nearby females in heat. Your puppy may start to display hormone-driven behavior, such as mounting, from four months on. While you may want to deter these actions, socialization is an important stage in your dog’s emotional development.  

My female dog needs to have at least one season before being spayed 

This myth may only apply to certain large breed dogs. You should consult with your veterinarian during your large dog’s first year to determine the best course of action. Otherwise, most female dogs can be spayed around six months of age or younger, before their first season. A dog can get pregnant even on its very first estrous cycle, so you run the risk of an unintended litter if you wait. Furthermore, spaying may help significantly reduce the risk of breast cancer or ovarian cancer in your dog’s later life.  

Spaying or neutering will alter my dog’s personality  

An intact dog is no more truly itself than a neutered one. Hormones do not determine personality! In fact, spaying and neutering can reduce unwanted behaviors, such as mounting, urine spraying, or fighting. You may find your male dog is actually more manageable after he is neutered, meaning you can enjoy his unique personality without worrying about any unwanted hormone-driven aggression or attempts to escape.  

You can separate a pair during “mismating” 

If you do find your intact dog engaged in mating with another dog, sometimes called “mismating,” it is not possible to separate the pair. Forget buckets of cold water or shouting, you cannot and should not physically separate the pair. Any attempts to do so risk injury and at the least will distress the dogs. The best course of action is to wait until they’re finished and take the female to a veterinarian as soon as possible.  


Female dogs go through a four-stage fertility cycle 

A female dog will generally go through two estrus or “heat” periods per year. These cycles may be more closely spaced in smaller dogs, or more spread out in large breeds. Each heat period typically lasts two to three weeks. The dog reproduction cycle can be broken down into the following four stages.  

  • Proestrus: The first 7-10 days of the heat cycle. Male dogs will become alerted to the female, but she will not allow mating. You may notice bleeding.  
  • Estrus: The mating period. This typically lasts 5-10 days, during which time bleeding will cease. This is the time the dog will accept mating.  
  • Diestrus: This period can last 10-140 days, depending on whether the female was impregnated or not. The pregnancy phase occurs in diestrus.  
  • Anestrus: The resting period between diestrus and the start of the next heat cycle.  

Dogs don’t go through menopause  

A female dog can get pregnant from her very first season right through her life cycle – that means dogs don’t go through menopause and remain fertile during their entire lifespan.  

Despite this unfailing fertility, late-life pregnancies are a high risk for a geriatric dog. Dogs as old as 12 can theoretically birth a litter, however, this can result in complications for both mother and puppies. “Whelping” or labor can be much more difficult and dangerous for an older dog and will likely result in a higher mortality rate among the litter. In addition, nursing is very physically demanding, especially for an older dog, and may require you to intervene and provide additional milk.  

Leaving dogs “intact” comes with health risks or hormonal behaviors 

If you should choose to not spay or neuter your dog, you’ll have to remain far more vigilant to their behavior and health.  

When it comes to intact male dogs, you may be in for a lifetime of “marking:” the action of establishing territory and fertility by spraying a small amount of pee on upright surfaces. This is particularly unpleasant and smelly when done inside the home. Furthermore, since male dogs are not cyclical in their sexual activity, a male can be aroused by the presence of any “in heat” dog at any time – even from a surprising distance. Once your dog senses a female, instinct will kick in and he’ll attempt to get to the fertile female by any means necessary. Suddenly your dog has become the ultimate escape artist, exhibiting destructive and sometimes aggressive behavior to remove any obstacle or animal in his path to fatherhood. Neutering will reduce the instinct to mark objects and the hormone-driven reproductive instincts that can make him aggressive or unmanageable.  

In females, the risks of remaining intact are more concerned with health than behavior. As previously mentioned, pregnancy in elderly dogs can lead to dangerous complications for mothers and pups. In addition, females will be much more susceptible to breast cancer, ovarian cancer, and pyometra. The latter is a painful uterus infection that requires urgent surgical intervention.  

Bottom line 

Ultimately, dog reproduction and fertility is no simple issue, but the health and safety of your dog is of paramount importance. Because of this, the decision to spay or neuter your pet is the best choice for their lifelong health and well-being. If you have further questions or concerns, you should contact your veterinarian to discuss the best course of action.