When Training Alone Just Doesn’t Work…Stress Can Alter Physiology

By: Eileen Koval, CDBC, CBCC-KA, CPDT-KA, MSc

While on a neighborhood walk, a large off leash dog suddenly appears and is charging toward you.  His body appears tight and tense with his head low.  You start to panic wondering how to protect yourself and your dog.  Your heart begins to race, your pupils dilate, breathing quickens, you start to sweat as you feel a surge of energy from a release of glucose, cortisol and adrenaline.  Then, suddenly, the dog veers off into a backyard and the owner shuts the gate behind him.  You realize that you are safe.  Your heart rate and breathing begin to slow back to normal, your body temperature cools back to normal, the panic and hypervigilance about your surroundings subsides.  You are able to go about your day like normal after a short period of time.

That is a normal stress response.  However, in some dogs (or people, or other mammals) these neuroendocrine responses are blunted, impaired, or otherwise dysregulated and do not function properly for the individual (Wulsin et al., 2016; Cotella, et al., 2019).  Individuals may be unable to explore and relax in new environments.  They may display disproportionate behavioral responses to sudden changes in their environment or other stressors.  They may struggle to form proper social bonds and lack appropriate social communication, even displaying heightened levels of territorial behavior.  They may display inappropriate reactivity or aggression.  They may struggle to cope with new situations despite regular, on-going socialization.  They may be completely shut down around new people or in places outside the home despite repeated and on-going exposure to people and new environments.  They may have heightened reactions to small stressors and appear unable to calm down after stressful events. 

The body is failing to respond to stress properly at the physiological level, rendering the animal incapable of coping and responding appropriately.

This is when a behavioral issue is both a welfare and a medical issue, but to many people, the resulting behaviors may look like problematic issues for a trainer.  Rescues may advertise these dogs as simply needing time and love, but there is sometimes more underlying when there are past histories of stress or neglect. Training alone is not going to solve an underlying medical issue.  This does not mean that training is useless.  It can reduce fear, reduce stress and teach new behaviors.  However the issues will very likely continue, welfare will be impacted, and impacts to normal behavioral functioning will continue if qualified medical professionals are not brought on board to help address the underlying medical issue.  In these dogs, there can be negatively impacted neuroendocrine system including the hypothalamic-pituitary-adrenal (HPA) axis that prepares the body to respond to stress in the environment. As a result, problematic behaviors frequently appear and remain at some level despite extensive efforts working with trainers or behaviorists on behavioral modification.  The long-term impact to the individual can vary depending on the age of individual during the chronic or acute stressful events.  The sex of the individual also impacts the long-term effects they suffer, too.  This highlights how the body is reacting and responding to its environment, which can result in permanent neuroendocrine changes.  These changes may compromise the individual’s ability to respond and behave appropriately in the future (Cotella et al., 2019; Wulsin et al., 2016; Miller et al., 2022). It is important to avoid stressors when possible, but also to recognize when problematic behaviors are a lot more than a simple training issue. Swift intervention utilizing integrative approaches with veterinary professionals will help to address the underlying issues, yielding the best chances for improved welfare and behavioral outcomes.

Stress while in-Utero – Long-Term Effects

Acute stress suffered by the mother while animals are in-utero can have lasting physiological, neuroendocrine, and behavioral impacts.  Guinea pig mothers were exposed to strobe lights for two hours on a single day during pregnancy/gestation.  As a result, offspring had significantly reduced body weight post-weaning and suffered long-term changes to the HPA axis (the body’s threat response system) .  Offspring displayed significantly increased cortisol (stress hormone) responses to ACTH stimulation, with many offspring suffering very high cortisol levels throughout the day and drastically low testosterone levels.  Offspring also displayed hyperactivity, but also an unwillingness to explore new spaces.  Offspring also developed increased brain-to-body ratios.  (Kapoor & Matthews, 2005). 

Animals suffering from these physiological changes are likely to be very fearful and anxious due to the constantly high cortisol levels throughout the day, even in the absence of any specific stressor.  They were also likely to display moodiness, irritability, or emotional reactivity due to the elevated cortisol responses to ACTH stimulation.  Given the high cortisol levels and hyperactivity, the animals likely experienced hyperarousal much of the time which could affect reduce their thresholds in changed or stressful situations.  This can lead to disproportionate reactions in overstimulating or stressful situations (Kapoor & Matthews, 2005).  Aggressive behavior is also possible in response to provocation or threats due to very high cortisol levels and decreased testosterone.  The very low testosterone levels would also contribute to possible timidness, fearfulness, anxiety, and decreased social behavior.  All of these factors are likely to reduce their willingness to explore new spaces, which was what the researchers observed during the experiment (Kapoor & Matthews, 2005; Mârza et al., 2023; Zhao et al., 2023).  Two hours of intense, acute stress while in-utero can result in massive, life-long changes to off-spring that are not going to resolve from a training approach alone, since that would not address the underlying neurobiological issues.

Stress during Adolescence – Long-Term Effects

Females appeared to suffer worse effects than males, but both suffered long-term behavioral and physiological changes from several weeks of varying chronic stress.  A study of male adolescent rats exposed to mild stressors (e.g. tilted cage, damp bedding, physical restraint; predator odor) two times per day for six weeks yielded long-term physiological and behavioral changes.  The adolescent rats exhibited much lower levels of immunoreactivity in the paraventricular nucleus of the hypothalamus (Cotella et al., 2019).  In a different study, female adolescent rats were exposed to variable chronic stress over a two-week period.  The female rats displayed a blunted HPA axis response – basically, an inability of the body to respond appropriately to stressors.  They had low morning corticosterone levels (a stress hormone in rats, similar to cortisol) and lower ACTH levels.  Similar to the other study on adolescent rats, they suffered changes to the functioning of the paraventricular nucleus of the hypothalamus with lower vasopressin mRNA expression (Wulsin et al., 2016).  Vasopressin is important for proper social communication and exploratory behavior.  These disruptions could be exhibited behaviorally through poor social behaviors or even the development of territorial behavior (Rigny, 2022).  In both studies, the chronically stressed rats also displayed much longer periods of immobility, which is associated with being depressed.  Male rats spent longer periods of time immobile while in new situations like a maze (Cotella et al., 2019).  Two other studies of mice revealed that the mice behaved in an ever-present anxious state following chronic stress that resulted in lasting HPA axis hyperactivity – a constant high state of anxiety and stress and over-responsiveness to stressors in the environment (Miller et al., 2022; Borrow et al., 2019).

Animals suffering these physiological changes are likely to be anxious and fearful with exploring new objects, people, or environments due to the increased cortisol levels.  They would likely react with intense fearfulness to acute stressors.  Their emotional thresholds for what is perceived as threatening may be reduced, so they will likely react disproportionately to perceived threats.  Mood changes are also likely over time, such as depression, irritability, or even aggression (Planchez, 2019; Carpenter et al., 2007). 

Stress during Adulthood – Long-Term Effects

Adult rats exposed to variable chronic stress over several weeks suffered lasting physiological impacts with long-term dysregulation of the HPA axis – basically, they did not respond appropriately at the physiological level like a healthy individual to stressors.  They had very heightened adrenal responses to stress, consistently high cortisol levels and took much longer time to calm down to baseline after a restraint test.  Fortunately, the adults fared well in reaction to acute stressors, avoiding any long-term behavioral or physiological effects. However, chronic stress in rats in adulthood resulted in permanent changes, revealing how the body is re-shaping and re-organizing how it operates in response to stress and experiences (Cotella et al., 2019).

Unsurprisingly, animals enduring these physiological changes will likely display fearfulness with exploring new objects, people, or environments due to the consistently elevated cortisol levels.  They may be more likely to freeze or hide in these situations, or alternatively, some animals may display pacing, frustration, and hyperactivity.  They would likely react with intense fearfulness or reactivity to acute stressors due to the heightened adrenal responses.  Their emotional thresholds may be reduced, resulting in them perceiving minor stimuli as threatening more frequently than a healthy animal.  In turn, they are more likely to react disproportionately to perceived threats.  Mood changes are also likely to develop, including depression, irritability, or even aggression (Planchez, 2019; Carpenter et al., 2007). 

Hypothalamic- Pituitary- Adrenal (HPA) Axis

(Romero & Butler, 2007; Plusquellec & Lanoix, 2013)

Does Genetics Influence Reactions to Early Stressors?

               Animals may have different reactions to stress in their environment due to their genetics.  This is especially true with dogs, many of whom have been selectively bred by humans over countless generations for specific temperaments and very specific behaviors to assist humans.  Domesticated animals, overall, tend to have low HPA-axis reactivity which increases their tameness and calmness with humans.  They face less environmental threats to their survival due to living in the care of humans, so high HPA axis reactivity is less important to their survival than it would be to animals living in the wild (Fallahsharoudi et al., 2015).  Just looking at dog breeds, we see a lot of variety in their sensitivity to stress, handling, interactions with unfamiliar people and new environments.  Some are specifically bred to react in these situations, particularly in guarding and herding roles.  Dogs displaying aggression toward humans were found to have drastically higher cortisol levels than dogs who did not display aggression (Rosado et al., 2019).  Similarly, MacLean et al. (2017) found that dogs displaying aggression had much higher vasopressin levels than non-aggressive dogs.  Since vasopressin is part of what initiates the stimulation of the HPA axis, both of these studies indicate a likelihood that aggressive dogs may have high levels of HPA axis activity.

               Unfortunately, many trainers and owners seek to eradicate the problematic behaviors using aversive methods, such as shock collars.  Some trainers even use reward based methods first, but then escalate to aversive (physical punishment) when that does not work. This is a failure to realize that some issues are actually medical in nature and not simply training issues. Can you imagine being hit, shocked, or choked for suffering from a medical issue? It happens a lot in the US with pet training, unfortunately. In reality, shock collars are actually found to induce negative physical changes and activation of the HPA axis.  Mice that were subjected to escapable moderate-level foot shocks developed a larger hypothalamus and appeared to be in an anxious and fearful state.  They were less exploratory when placed in novel situations like a maze.  They displayed enhanced retention of fearful memories when placed again in contexts that resembled the foot shocks.  The researchers described the findings as comparable to those seen in human PTSD patients (Balatskyi et al., 2025).

Research has repeatedly shown that dogs exhibit significant pain during shock collar training and have elevated levels of cortisol (Mârza et al., 2024; Schilder & van der Borg, 2004; Beerda et al., 1998; de Castro et al., 2020).  Dogs subjected to this type of training are known to vocalize, defecate themselves, yawn, lick lips, restlessness, display lower body posture and other signs of fearfulness, anxiety and stress during training.  These behavioral stress signs and the elevation of cortisol levels are worse when there is no warning signal that a shock may be coming.  The dogs frequently associate the owner with the expectation of receiving a shock, resulting in poorer welfare outside of training contexts.  These dogs also have been shown to exhibit elevated cortisol levels outside of training contexts.  They are also more likely to exhibit fearful and aggressive behaviors.  Serious signs of compromised welfare with shock collar training and other aversive training are apparent across a plethora of studies.  These behavioral observations and biomarkers data described above appear consistent with potential signs of neurobiological changes due to stress (Beerda et al., 1998; Mârza et al., 2024; Schilder & van der Borg, 2004; Cooper et al., 2014; Schalke et al., 2007; de Castro et al., 2020).

Integrative Approaches to Help These Dogs

Taking measures to avoid and mitigate stress as much as possible is essential to helping prevent these issues from developing.  Even adult dogs, as discussed, can develop physiological changes after enduring periods of chronic stress.  It is crucial to look for signs of stress in our dogs and respond swiftly to mitigate this.  The stressors may not be obvious but could be changes in household members, changes to household routine, social isolation, conflict between other animals or people, pain/discomfort issues, frustration during training, lack of control in their life when no one acknowledges the needs they communicate, climate/temperature changes, lack of welfare needs being met, lack of autonomy and choice in their life (remember…pets are captive animals), amongst other things.

Studies have shown SSRIs and TCAs (e.g. fluoxetine/Prozac, clomipramine/Clomicalm, etc.) help restore proper functioning to the HPA axis when dysregulation has occurred.  It is essential to seek the help of a qualified veterinarian (one with education/experience in behavior medicine) who can appropriately evaluate, diagnose and treat the animal.  Appropriate treatment can be combined with emotional and behavioral modification training to help animals learn to cope with environmental changes, create positive emotional associations, reduce frustration and fearfulness, and teach new ways to navigate social and physical environments (Heinzmann et al., 2011; Tafet & Nemeroff, 2020).  There is a lack of public awareness that stress can actually alter physiology, and that this can actually be a medical issue.  Not every behavioral issue is simply a training issue.  To me, it is a serious welfare issue when trainers, rescues, or pet parents would rather a dog suffer from severe fearfulness and anxiety than see a veterinarian about the possibility of medication to address the underlying issues.  Sometimes they would rather seek the help of an aversive trainer than a veterinarian, when we know that aversive training like shock collars is more likely to CAUSE these issues than to alleviate them.  Without proper threat response system and other hormonal functioning, the animal does not have the chance to cope with stress and respond to their environment appropriately.  If this goes on for long periods of time, then maladaptive behaviors will likely result as they attempt to cope.  Be quick to involve a veterinarian to ensure the best outcomes possible.  My hope in writing this heavily researched article is that people may have a fuller understanding of mitigating stress in animals and seeking the help of a veterinarian in addition to a qualified behavior consultant or behaviorist (not a trainer) who utilizes reward based methods when serious emotional and behavioral issues occur. 

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References:

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Eileen Koval, CDBC, CBCC-KA, CPDT-KA, MSc (in Operations Management) is a fully certified dog behavior consultant with the International Association of Animal Behavior Consultants (IAABC). She is currently working toward an M.S. in Applied Animal Behavior and Welfare at Husson University. Eileen believes that the foundation of a good cross-species relationship is understanding the needs and normal behavior patterns of each dog as an individual. She enjoys helping humans and dogs communicate more effectively to create brilliant relationships filled with joy, purpose, and fulfillment for all species involved. Eileen offers private consulting for serious dog behavior issues, obedience/manners, and agility training. She developed a unique online course to help pet parents and trainers develop reliable snake avoidance behavior off-leash through positive reinforcement techniques. These techniques have been applied by trainers worldwide to teach dogs reliable avoidance of dangerous environmental hazards and off-leash property boundaries. Eileen lives on a small ranch in Las Vegas, Nevada, with her husband and their Nederlandse Kooikerhondjes.