A recently published study indicates that it is likely that dogs dream about their owners and that large dogs dream for longer than smaller canines.
The results of this study do not surprise me. I am now working with my fourth guide dog and have, from a young age grown up around dogs. Dogs wag their tails and perform other activities, such as running, growling or yelping while asleep. It is therefore logical (to my mind at least) to assume that our four-legged friends can (and do) dream. Anyone who has grown up around dogs will have observed them growling while asleep which indicates that they (like us) also experience nightmares.
http://www.themonitordaily.com/dogs-dream-owners-study-says/212676/