There are many different terms for pet desexing. It can also be called spaying, neutering or simply having your pet fixed. When a male dog is fixed, what does it actually fix? You might have heard that desexing a male dog can reduce their level of aggression, but this isn't necessarily true, and it's not something that would be evident. Having said that, there are a number of positive behavioural changes (potentially including their aggression levels) that your dog should begin to exhibit after he has been desexed.
Early Age Desexing
It's important to note that dog desexing can often take place well before puberty, which can occur anywhere between seven months and two years of age. The best time to desex your dog can vary depending upon their projected size and weight as an adult, and the procedure can be performed when your dog is as young as eight weeks. This is known as early age desexing (EAD) and is, in fact, standard procedure at the RSPCA. So desexing can predate puberty by a considerable margin, meaning it's not an automatic guarantee that the process will reduce aggression in a dog since these types of behavioural changes might only begin to show once your dog matures and goes through puberty.
Because the desexing took place before your dog has reached physical maturity (and by extension, sexual maturity), it can be difficult to gauge whether the procedure had any effect on their aggression levels. A direct comparison can only be possible when an aggressive adult dog is desexed, allowing you to note whether or not there have been any observable changes to their aggression level after the desexing. A dog that has undergone EAD might still develop aggressive tendencies as they mature, and this is best overcome with training and, if necessary, behavioural therapy.
Positive Behavioural Changes
There are still numerous positive behavioural benefits to having your male dog desexed at a younger age. He will refrain from numerous acts of territorialism because he never instinctively developed them. This includes scent marking with his urine. He will also not develop many attributes related to his sexuality that can be interpreted as aggressive, such as mounting your leg or behaving in an aggressive manner towards female dogs that are ovulating.
Desexing can have an effect on your dog's aggression levels, but this is not always the case and can be difficult to conclude when the desexing is performed before puberty. But there are a great number of positive behavioural changes that are associated with desexing in any event.