It's bad news for dog owners who have to leave their pup at home during the day.
"They do get sad," says Bradshaw. "Dogs are very attached to humans. It's the way they live alongside us, by watching us and trying to work out all the time what we're thinking and what we're doing. When we're not there, they feel disoriented and anxious."
Different dogs will express this in different ways – Border collies tend to pace around because they're quite active, whereas Labradors are more likely to chew on things. "Each dog has a different way of expressing its distress – some will pace, some will howl, some will bark, some will scratch at the door or dig in the sofa," says Bradshaw.
Even if your dog just curls up and goes to sleep while you're out, seemingly peacefully, that doesn't mean they're not stressed.
In an experiment Bradshaw ran with Channel 4, he filmed dogs that were left at home during the day to see what they did. Dogs that didn't look stressed during the time their owner was out still had high levels of stress hormone in their urine. "It shows that the dog has come to learn there's nothing it can actually do to make the owner come back, but it's anxious and stressed all the time the owner's out," he says.
But all hope is not lost, because there's a training scheme, developed by Bradshaw and available from the RSPCA website, you can use to help your dog feel more at ease when you're not around.