You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Dogs are social animals that demonstrate emotional behavioural changes when there are changes in their group

Dogs are social animals that  live in groups or packs. In a typical household the humans are dominant members of "the pack" over the pet dog. Evidence from studies conducted in various species of mammal and bird shows that the formation of an emotional bond with other members of the same species, or with members of a different species (such as humans) is an instinctive response that is independent of factors in the external environment. 

Young animals automatically become attached to individuals and objects with which they come into contact, especially during the critical period from about 3 weeks of age to about 8 weeks of age. During this early period a puppy will quickly determine which animals and humans will become it's closest social relatives. Strong emotional bonds of this type can be formed throughout a dogs life, but the amount of time exposure required is greater.

Dog behaviour revolves around a social pecking order whereby some individuals are dominant to others. When two dogs  form a social bond one will be dominant and the other subordinate, but the dominance may not be observed as pure aggression. 

In interpreting the behaviour of dogs we must be careful not to apply the attributes of human behaviour (anthropomorphism) without properly conducted scientific studies to determine the exact nature of the behaviour. Dogs sometimes show behavioural traits that appear to be so similar to our own, that we assume the basis to be the same. Two interesting examples are :

1) Jealousy.  In one study a puppy was removed from a litter for a period and then put back. It's littermates frequently threatened the puppy and showed aggressive behaviour towards it. This was initially thought to represent "jealousy" towards the puppy being returned to the litter. Closer examination showed that the fighting was confined to individuals which had not yet established a definite dominance relationship with the puppy and so "jealousy" was a misinterpretation. Replacing the puppy simply stimulated the need to establish it's place in the pack with the individuals with which it had not yet established a dominance relationship.

2) Mourning. There are numerous anecdotal reports about dogs apparently "mourning" after the loss of a close canine or human companion through death or physical removal. Often the "mourning" is manifest as a change in normal behaviour precipitated by the removal of the other individual from the dog's environment. A change in behaviour is not a surprise because dogs are animals of habit, and they have a daily routine. If that routine is broken because a companion is removed from the environment the dog will need to readjust it's behaviour. Periods of play may be replaced with periods of resting which may be misinterpreted as periods of depression, or sulking. In other situations a dog may continue with established behaviour patterns even though the companion is no longer present. A good example of this was a dog that continued to visit a railway station to meet the train that it's owner used to arrive home on for years after the owner had died. 

The companion animal-human bond is an extremely complex relationship from which both dogs and humans benefit and the way in which humans and dogs respond to each others behaviour is fascinating to observe, although sometimes difficult to interpret accurately. Understanding behaviour in these dog-dog and dog-human relationships is important when canine behaviour becomes socially unacceptable - for example when a dog barks continuously for long periods, or if a dog becomes aggressive towards humans, and animal behaviourists spend much of their time interpreting behavioural changes so that they can devise solutions to behavioural problems.

Behaviour is controlled by hormones and brain activity - which can be influenced by many factors including disease processes. So, if your dog shows a sudden change in behaviour it is advisable to ask your veterinarian to examine it because there may be a medical reason as well as a behavioural reason for the change.

Updated October 2013