You just got the most adorable puppy and you want to breed him. But when can male dogs breed, and should you be concerned about leaving your puppy intact? Here's what the research says.

When Can a Male Dog Breed?

The age at which a male dog reaches sexual maturity can vary with breed. However, most males are able to successfully breed by six months and reach full sexual maturity between 12 and 15 months. Smaller breeds mature faster than larger breeds, allowing for that big range.

Male dogs can continue to breed into old age and can breed at any point in time. That being said, unless special documentation is provided, American Kennel Club rules and regulations don’t allow for registration of a litter from a sire, the term for "intact" males, that is either less than seven months or greater than 12 years at the time of mating.

It is believed that, although intact male dogs can sire a litter at any point once sexual maturity is reached, they have the highest testosterone levels and are the most fertile in that 12–15 month age range. During this time, you may see your dog exhibiting such behaviors as urine marking and roaming. These are typical behaviors of any intact male dog, but are especially common during this age period. 

Are There Behavioral Consequences of Not Neutering?

It has been a long-held belief that the increased testosterone levels in intact males lead to more aggression than their neutered counterparts. However, further research has determined that a dog's aggression is more complex than whether or not they are neutered. One study showed that dogs that belonged to first-time owners, those with less obedience training, or simply those purchased to guard or to be given as a gift were more aggressive. Another article discussed the presence of different environmental factors, including food aggression within the first two months in the home, sleeping in the bed of someone in the home within the first two months, and even living in a home with one or more teenagers.

The behaviors of urine marking and roaming, as well as the belief, whether founded or not, that intact male dogs are more aggressive, can drive the age at which some pet owners may pursue neutering. For most dog breeds, veterinarians recommend neutering at 6 months of age, since this is the age when many dogs reach sexual maturity, and an encounter with an unspayed female dog could lead to an unwanted litter.

Health Considerations of Neutering

With the release of more research, more veterinarians are recommending waiting a little longer to neuter large and giant breed dogs because they mature more slowly than smaller breed dogs. Some veterinarians now recommend waiting until between 11 and 12 months of age for large breed dogs and will even push out neutering to 14 months of age for giant breed dogs.

One study looking at the risks of orthopedic conditions, including elbow and hip dysplasia and ACL injury, showed that there was actually a significant increase in risk of the orthopedic conditions in dogs that were neutered before reaching sexual maturity. This is believed to be because of a relationship between hormone concentration and the growth of the long bones. If you have a large or giant breed dog, discuss with your veterinarian the best time to neuter your specific dog.