Attempting Dominance
Growling may be a sign of dominant behavior. If you fail to establish a dominant position, your dog is likely to take over and assume the leader position. He will growl and be aggressive or even bite to maintain his dominant position.
Dominant dogs may be trained and can become obedient.
When choosing your dog you need to get a dog that is suitable for your personality; there are certain breeds that have a propensity to dominate and if you don't have an authoritative personality you need to avoid these breeds.
Excitement
Dogs may growl while playing if they become over excited. If you notice this, try to slow down the pace of the game.
Protective Growling
Dogs tend to be territorial and they may growl when an intruder is on his territory. Also, dogs are very protective of their food, so if someone approaches his food bowl he will growl.
Fear Related Growling
Dogs may growl when they are afraid of something. Fear in dogs may be triggered by different objects, noises or people; the fear can be so intense that the dog may temporarily lose his sight or hearing, so he will try to compensate by growling. A dog that is afraid may become aggressive.
Rage Syndrome
The rage syndrome is more frequent in certain breeds such as springer spaniels. The syndrome causes sudden rage in the dog and is displayed in episodes. A rage episode starts by growling and the dog may become aggressive.
The rage syndrome is a rare condition and is actually a seizure which originates in the right lobe of the dog's brain.
The condition may be controlled with medication such as Phenobarbital.
The rage syndrome can be mistaken for dominant or fearful behavior; however, dogs suffering from the rage syndrome will display unpredictable episodes of aggression, while dominant or fearful dogs have always a reason to be aggressive.
Pain
If your pet is in pain he may growl. The pain may be caused by a wound or undetected illness. If your dog growls frequently, you need to consult the vet.
Irritation
Irritation may trigger growling. A dog may be irritated by another dog or person. Irritability may also be caused by pain. Dental or joint pain can be unbearable, so the dog will be aggressive.
Growling is among the numerous signals of canine communication. Your dog may signal that something is wrong, so you need to detect the cause and apply suitable treatment.
If your dog becomes aggressive after growling don't punish your dog, as this may cause more aggressive behavior.