A new study explains why punishing your dog, by yelling, for example, may not be a good idea.
What is the best way to get dogs to stop chewing on the carpet, peeing on the floor, and barking at the doorbell?
Some dog owners tend to punish their pets by yelling or otherwise reprimanding them verbally, but research shows that these and other negative methods, though effective, can raise stress levels in the animals.
In fact, a previous review of 17 studies that looked at the effects of different training methods on dogs found that aversive training methods, such as punishment, are in no way more effective than positive reinforcement methods.
The same review also found that aversive training and punishment can endanger a dog's physical and mental health.
However, the older studies in the analysis mostly included police dogs and dogs bred in laboratories for research.
Few studies have looked at pet dogs, and now, researchers have aimed to rectify this by examining the effects of routine punishments on 92 companion dogs.
Ana Catarina Vieira de Castro, Ph.D., from the University of Porto, in Portugal, is the lead author of the study, which appears on the server bioRxiv ahead of print.
Testing the short term effects of punishment
De Castro and the team started from the hypothesis that dogs trained using an aversive method would display more behavioral and physiological markers of stress. Secondly, the researchers believed that these dogs would make more "pessimistic" judgments in cognitive bias tests.
The researchers recruited 42 dogs from training schools that used reward based methods to encourage good behavior. In these schools, dogs are rewarded with food or play for good behavior.
The team also recruited 50 dogs from aversive programs, where yelling and leash-jerking are routine elements of training.
De Castro and colleagues filmed the dogs during training and took saliva samples before and after three training sessions.
The videos revealed that the dogs displayed more signs of stress, such as lip licking and yawning, and appeared to be more tense. Such indicators did not show up among reward-trained dogs.
Furthermore, saliva tests showed raised levels of cortisol after the aversive training sessions, whereas the dogs in the reward training programs did not show any changes in cortisol.
Punishment makes dogs more pessimistic
Then, the team wanted to see whether the effects of aversive training would linger in the long term. To this end, they designed a cognitive bias task and used it with 79 of the 92 dogs, because some owners were unavailable, to see how the dogs reacted to the prospect of a food reward.
In the task, the dogs were trained to associate one side of the room with a sausage. Bowls in that side of the room would contain sausages all the time, whereas bowls on the other side of the room did not.
Then, the scientists placed an empty bowl halfway between the two sides of the room. The bowl smelled of sausage, but the dogs could not see whether it was empty or full.
By timing how quickly the dog would run to check the bowl, the researchers determined their optimistic or pessimistic behavior.
In standard tests like these, the assumption is that an optimistic dog would run excitedly to the bowl, thinking it contains a food reward, whereas a pessimistic dog would be less eager and move more slowly.
In the current test, the team consistently found that dogs trained with the aversive method were more pessimistic. In fact, the more the dog had been punished, the more pronounced were the findings.
"Our results show that companion dogs trained using aversive based methods experienced poorer welfare, as compared to companion dogs trained using reward based methods, at both the short and the long term level," the authors conclude.
Furthermore, they write, "This is the first comprehensive and systematic study to evaluate and report the effects of dog training methods on companion dog welfare." The authors continue:
"Critically, our study points to the fact that the welfare of companion dogs trained with aversive based methods appears to be at risk."