The response that each dog has to the loss of an owner can be as varied as those displayed by humans in mourning. Dogs do feel emotion and will show signs of sadness, but the ways that sadness is revealed and the extent of its impact are completely up to the dog in question and the dynamics of the relationship.
Any type of change can upset your dog, but the pain that loss brings can cause a reaction that goes beyond the norm. Some dogs are closer to their human guardians than others due to living arrangements or the time spent together. Monitor any dog who has lost his guardian for changes in behavior and general sadness. Only by noticing a change can you take the necessary steps to bring the animal back to mental and physical health.
The signs of a mourning dog can range from subtle differences in mood to outright depression. After losing a guardian dogs may eat less, drink less and even voice their sadness with howls and whining cries. Some dogs will stop their typical playful behavior and display indications of fatigue and sleep more than usual. Negative body language will also betray the animal's feelings as he moves more slowly and deliberately and shows less enthusiasm than before. Some dogs may even begin to look or camp out in places where their guardian spent a lot of time when living.
As time passes, the dog should steadily progress to a normal state of being. If he continues to remain saddened without improvement, check if the cause is physical. Some injuries or illnesses can cause similar symptoms and must be treated if the animal is to recover. A veterinary check up will tell you if the problem is injury, illness or grief.
In most cases the dog will recover on his own if allowed the time necessary to overcome his loss. Do not change how you treat the dog. Instead, reinforce the status quo so he sees that things are continuing as normal and sadness is not going to take over. To help the process along, involve the animal in more physical activity than normal so he is challenged to move on, and his brain is forced to release the serotonin necessary to normal function.