Keep it kind!

That’s one way of summing up the findings of a new study by Portuguese researchers on the long-term negative effects of aversive training.

In their paper, “Does training method matter?: Evidence for the negative impact of aversive-based methods on companion dog welfare,” lead author Ana Catarina Vieira de Castro, PhD, and her colleagues at the University of Porto argue that, while the use of aversive-based methods has been strongly criticized for some years now, evidence to back up those claims has been lacking in the literature.

De Castro and company aimed to correct that lack by examining the effects of routine punishments on 92 companion-animal dogs. Other studies have focused on working dogs rather than pets.

The team 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. They also recruited 50 dogs from aversive-training programs, where negative conditioning techniques can include unpleasant sounds, physical corrections, harsh scolding.

Next, the researchers filmed the dogs during the first 15 minutes of four typical training sessions. Additionally, they took saliva samples from each dog at home to determine a baseline level, then again before and after each session.

After reviewing the videos, the team determined that the dogs who went through the aversive training displayed more signs of stress, such as lip licking and yawning, and appeared to be more tense. Dogs who underwent the reward-based training did not exhibit the same stress-related symptoms.

Furthermore, saliva tests showed raised levels of cortisol after the aversive-training sessions, whereas the dogs in the reward-based sessions didn’t show any changes in cortisol.

Then, to see whether the effects of aversive training would linger in the long term, the researchers designed a cognitive bias task to be done one month later at home to see how the dogs reacted to the prospect of a food reward.

The task involved placing an empty bowl on one side of the room and a sausage snack on the other. By switching the placement of the bowls around the room to see how long the dogs would take to find the treat, the researchers found that the aversive-trained dogs tended to approach the bowls more slowly, indicating that they were less hopeful about finding anything in the bowls.

In contrast, the dogs who went through positive-reinforcement training were much quicker to approach the bowls, and exhibited far fewer stress behaviors. Their cortisol levels were lower, too.

The researchers write that, “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.”

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