Why you should never yell at your dog

A recent study has shown that dog training that uses punishment is bad for the mental state of animals.

Led by biologist Anna Catarina Vieira de Castro of the University of Porto, Portugal, an international team of scientists has conducted a new study with companion dogs.

The animals were recruited from canine kennels in Porto: 42 of three schools where training was based on food or play reward, and 50 dogs from four schools where training was based on threat and coercion - screaming, physically manipulating the dog and pulling the leash. ...

Each dog was videotaped during the first 15 minutes of training and saliva samples were taken to assess the level of stress (three from each dog) at home to determine the content of the stress hormone cortisol, and three more samples from each dog after training.

The researchers also analyzed the dogs' behavior during training to look for signs of stress - yawning, lip-licking, raising their paws, and squealing.

Unsurprisingly, dogs in schools where rudeness and coercion were used exhibited increased stressful behavior and higher cortisol levels when compared to a control home setting. In contrast, well-treated dogs were calmer, showed no signs of stress, and had low blood cortisol levels.