Dogs trained using aversive stimuli, which involve punishments for incorrect behavior, show evidence of higher stress levels compared to dogs trained with reward-based methods, according to a study publishing December 16 in the open-access journal PLOS ONE by Ana Catarina Vieira de Castro from the Universidade do Porto, Portugal, and colleagues.
The researchers observed the behavior of 92 companion dogs from 7 dog training schools in Portugal that use either aversive methods (which use mainly aversive stimuli), reward methods (which focus on rewarding desired behaviours), and mixed methods (which combine the use of both rewards and aversive stimuli).
They filmed training sessions and tested saliva samples for the stress-related hormone cortisol.
Dogs trained using aversive and mixed methods displayed more stress-related behaviors, such as crouching and yelping, and showed greater increases in cortisol levels after training than dogs trained with rewards.
The authors also conducted a cognitive bias test in an unfamiliar location outside of the dog’s usual training environment with 79 of the dogs, to measure their underlying emotional state. They found that dogs from schools using aversive methods responded more pessimistically to ambiguous situations compared with dogs receiving mixed- or reward-based training.
Previous survey-based studies and anecdotal evidence has suggested that punishment-based training techniques may reduce animal welfare, but the authors state that this study is the first systematic investigation of how different training methods influence welfare both during training and in other contexts.
They say that these results suggest that aversive training techniques may compromise animal welfare, especially when used at high frequency.
The authors add: “This is the first large scale study of companion dogs in a real training setting, using the types of training methods typically applied in dog training schools and data collected by the research team. The results suggest that the use of aversive training methods, especially in high proportions, should be avoided because of their negative impact on dog welfare.”
Funding: The current research study was supported by FCT – Fundação Portuguesa para a Ciência e Tecnologia (Fellowship SFRH/BPD/111509/2015) and UFAW – Universities Federation for Animal Welfare (Grant 14-16/17), with grants awarded to ACVC. SP was supported by PIPOL – Regione Friuli Venezia Giulia. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. FCT – Fundação Portuguesa para a Ciência e Tecnologia: https://www.fct.pt/index.phtml.pt UFAW – Universities Federation for Animal Welfare: https://www.ufaw.org.uk/.
To fulfil their increasingly important role as companion animals, dogs need to be trained to behave in a manner appropriate for human households. This includes, for example, learning to eliminate outdoors or walk calmly on a lead [1,2]. The fact that dog behavior problems are the most frequently cited reason for rehoming or relinquishment of dogs to shelters and for euthanasia  suggests that such training is often missing or unsuccessful.
Dog training most often involves the use of operant conditioning principles, and dog training methods can be classified according to the principles they implement: aversive-based methods use positive punishment and negative reinforcement and reward-based methods rely on positive reinforcement and negative punishment . There is a heated debate surrounding the use of aversive-based training methods, as studies have linked them to compromised dog welfare (e.g., [4–9]).
Some aversive-based tools, such as shock collars, have indeed been legally banned in some countries . However, a recent literature review by  concluded that, because of important limitations, existing studies on the topic do not provide adequate data for drawing firm conclusions.
Specifically, the authors reported that a considerable proportion of the studies relied upon surveys rather than on objective measures of both training methods and welfare; that they focused on sub-populations of police and laboratory dogs which only represent a small portion of dogs undergoing training; and, finally, that the empirical studies have concentrated mainly on the effects of shock-collar training, which is only one of several tools used in aversive-based training. In summary, limited scientific evidence exists on the effects of the entire range of dog training techniques on companion dog welfare.
Furthermore, previous empirical studies have focused on the short-term effects of training methods on dog welfare. Behavioral and physiological indicators of welfare, such as the frequency of stress-related behaviors and the concentration of salivary cortisol, have been collected in and around the training situation (e.g., [8, 11]; see also ).
However, the long-term welfare implications of training methods have not yet been examined. To our knowledge, only one study evaluated the long-term effects of training on welfare. Christiansen et al (2001)  found no effect of shock collar training on dog fear or anxiety; however this was based on dog owner reports of behavior and temperament tests rather than on objective and animal-based welfare indicators. Importantly, a suitable assessment of the effects of training methods on dog welfare should comprise an evaluation of both their short- and long-term effects.
Long-term (or chronic) stress can arise from the cumulative exposure to aversive experiences , which may reflect the experience of dogs trained with aversive-based methods. A body of research has shown that long-term stress is associated with changes in the long-term affective state of animals (e.g., [14–16]). One way to assess affective states is through the cognitive bias paradigm (e.g., ).
The cognitive bias task has been validated as an effective tool to evaluate the affective states of non-human animals and has been extensively used with several species, including dogs [17–19]. The rationale behind the paradigm is based on theoretical and empirical findings that an individual’s underlying affective state biases its decision-making and, specifically, that individuals experiencing negative emotional states make more ‘pessimistic’ judgements about ambiguous stimuli than individuals experiencing more positive emotional states [16, 18].
Therefore, the aim of the present study was to perform a comprehensive evaluation of the short- and long-term effects of aversive- and reward-based training methods on companion dog welfare. By performing an objective assessment of training methods (through the direct observation of training sessions) and by using objective measures of welfare (behavioral and physiological data to assess short-term effects, and a cognitive bias task to assess long-term effects), we addressed the question of whether aversive-based methods actually compromise the well-being of companion dogs.
We hypothesized that dogs trained using aversive-based methods would display higher levels of stress during training, as determined by behavioral and physiological indicators of stress during training sessions, and more ‘pessimistic’ judgments of ambiguous stimuli during a cognitive bias task performed outside the training context.
Understanding the effects of training methods on companion dog welfare has important consequences for both dogs and humans. Both determining and applying those training methods that are less stressful for dogs is a key factor to ensure adequate dog welfare and to capitalize on the human benefits derived from interactions with dogs [20, 21].
reference link : https://www.biorxiv.org/content/10.1101/823427v1.full