Irish wolfhounds are giant-sized dogs, and are amongst the tallest breeds in the world.
National Kennel Club veterinarian Becky Murphy said they were historically bred as combat dogs to watch over sleeping armies at night and later for hunting wolves.
"Maybe those instincts have come out for some reason ... All dogs do have that hunting pack instinct in the back there, and sometimes unfortunately it does come forward."
However, Irish wolfhounds were generally a sweet and gentle breed and were not normally involved in such attacks.
Otago Daily Times circulation manager Dave Bretz said in 20 years he had never heard of such an attack.
"You have the odd incidents. But for this to happen with someboy who was familiar, at least a little bit, with the animals, and wasn't some random dog that got out of somebody's property - this is very rare."
Mr Bretz said the animals involved were familiar to the woman, who shared four newspaper delivery rounds with her husband.