Most controlled scientific studies on this question (and there have been many!) show that whether a dog is spayed or neutered has no impact at all on the likelihood that they will be aggressive in any given circumstance.
The results demonstrated no reduction in aggressive behavior after surgical castration and a significant increase in dog-directed aggressive behavior after chemical castration.
Behavioral Changes in a Dog After Being Neutered
Removing the testicles removes the largest source of testosterone in the body. This results in a decrease in sexually driven behaviors in your dog: urine marking, escaping to seek female dogs, and aggression toward other male dogs.
According to the data, neutered male dogs are more likely to be aggressive toward intact males than intact males interacting with other intact males. And female dogs spayed later in life are less likely to show an increase in aggression than females who were spayed at a young age.
When to Neuter. The traditional age for neutering is six to nine months. However, puppies as young as eight weeks can be neutered as long as there aren't other health problems. An adult dog can be neutered at any time but there is a larger risk of complications.
"In general, a pet should be neutered as soon as he starts demonstrating naughty behaviors like being aggressive or dominant, marking territory, or trying to escape to find a mate," Nichols says.
Is it Too Late? The recommended time to spay or neuter a dog is six to nine months. But if your dog is healthy, there is no specific age limit to having the procedure done.
Dogs that have been neutered will not be free of hormonal behavior issues right away. This is because in most cases, it can take anywhere from two to four weeks, and sometimes even as long as six weeks, for all the hormones to leave your dog's body.
Studies indicate neutered males are susceptible to anxious or fearful behaviors, noise phobias, aggression, and undesirable sexual behaviors.
Even though there won't be a change in your pet's energy level, the act of having a vet spay or neuter your pet will eliminate or reduce those behaviors that are attributed to their hormones. This includes heat cycles and the associated behaviors in female dogs.
Benefits of Neutering (males):
Less desire to roam, therefore less likely to be injured in fights or auto accidents. Risk of testicular cancer is eliminated, and decreases incidence of prostate disease. Reduces number of unwanted cats/kittens/dogs/puppies. Decreases aggressive behavior, including dog bites.
In dogs, an incision is made in front of the scrotum, and both testicles are pushed through this single incision and removed.
If the dog is becoming aggressive (especially towards other male dogs), this is likely to be reduced (as a greater stimulus is needed to trigger his aggressive instincts). HOWEVER, the loss of self-confidence that (understandably! - Ed.) comes with castration may make him more prone to fear-based aggression.
Studies show, for example, that due to higher testosterone levels, intact male dogs between eighteen months and two years of age have a greater incidence of aggression than females or neutered males.
Many older dogs show increased aggression, anxiety, or compulsive behaviors. These behaviors are aggravated by body inflammation, sensory changes, and cognitive decline.
Health Benefits of Neutering
Neutering reduces marking in about 50% of dogs. Inter-male aggression can be reduced in about 60% of dogs. Dominance aggression can sometimes be reduced but behavioral modification is also needed for complete elimination.
Dog aggression can be related to fear, prey drive, socialization issues, and guarding territory, among other things. Most aggressive behavior in dogs stems from fear and anxiety, rather than the desire to hurt others. A certified animal behaviorist can help you safely deal with your dog's aggressive behavior.
On average dogs who are spayed or neutered live one and a half years longer than those who are not. Typically, dogs who are not fixed live to be about 8 years of age, where fixed dogs average about nine and a half years.
In early-neutered dogs, the incidence of CCL was 5.1 percent in males and 7.7 percent in females, suggesting that neutering prior to sexual maturity significantly increases a dog's risk of developing CCL disease. With respect to cancer, cases of lymphoma were 3-fold greater in the early-neutered males.
The pain associated with spay or neuter surgeries is typically more of a discomfort and may last for just a few days and should be completely gone after about a week. If your pet is experiencing pain or discomfort for more than a couple of days it's a good idea to contact your vet for further advice.
Yes. During the surgery your dog will be unconscious and not feel any pain however, once they wake up they will require medication to help with pain. When the surgery is complete, your vet will administer pain medications to your dog via an injection. This long-term pain medication should last for about 12-24 hours.
Either way, it is very important that you limit your pet's movements during the 7 to 10 day recovery period, as strenuous activity, such as running, jumping or playing, could disrupt the healing process and even cause the incision to become swollen or open.
A study in 2018 of over 13,000 dogs across America found that neutering, at any age, didn't affect the likelihood of a dog showing aggressive behaviour towards humans or dogs who they already know. So to summarise – behaviour is how we see our pets' personalities, and is affected by multiple factors.