Stress has an effect on a dogs physiology and psychology. When a dog experiences stress, four key hormones are released to help prepare them to respond; Adrenaline increases heart rate, blood pressure, fatty acids for fuel and blood sugar whilst inhibiting digestion and perception of pain, Cortisol increases glucose, fatty acids and amino acids, Aldosterone regulates blood pressure and water balance and Testosterone builds muscles and is connected to higher levels of aggression.
Short term stressors are things like passing a barking dog or being startled by a noise. During short-term stress, dogs will chose a coping mechanism; fight, flight or freeze. They may display behaviours such as lunging, growling, whale eye, vocalisation, piloerection, tense body, tail tucked under, displacement behaviours, hiding, panting, hyperactivity, drooling, sniffing, yawning, paw lifts and shake offs. They may also self mutilate, pace and spin. When the hormones are released as part of the stress response, they are essentially in a loop. Once they reach a certain level they stop releasing as to regulate the body. As long as the stressor is short-term then this loop can maintain itself. This creates ‘optimum efficiency’ (Schloz & Von). The increased heart rate, blood pressure, breathing and energy is what enables a dog to be successful in problem solving situations like training or hunting. It is also necessary to develop a greater resistance to disease and stress itself. A puppy who has successfully coped with short term stress is more likely to be able to cope with stress in adulthood.
However, long term stressors put the dog in a state of distress for a prolonged period of time. This might be the continuous use of harmful training aids or separation anxiety. These kind of stressors can cause more lasting damage to a dog. It can cause low energy, lethargy, loss of appetite, insomnia, depression, high blood pressure, hyper vigilance and reactivity. It can even affect the brains function and structure and result in more serious medical conditions that would need veterinary assistance, such as gastrointestinal diseases, dermatologic conditions, respiratory and cardiac conditions. If a bitch is pregnant then there can also be an effect on the foetuses she is carrying. Cortisol causes the placenta to shrink and overwhelms the bitches enzyme that helps to protect against stress (Holmes, 2013). This can result in brain defects due to the lack of nutrients flowing to the puppies as well as producing smaller newborns. Holmes’s study also found that the puppies are more likely to develop mood disorders. Cortisol levels take around 60 seconds to reduce by half during short term stress, but during long term stress cortisol levels are quadrupled (Weitzman). This means that the stress response loop breaks down and the body is no longer able to regulate itself. It can take days, even weeks for the cortisol to fall again which is why it is so important we are continuously monitoring our dogs arousal bucket.
References
Holmes (2013) Perinatal programming of stress related behaviour by glucocorticoids. British Neuroscience Association.
Scholz & Von Reinhardt (2006) Stress in dogs. Chapter 3, page 15.
Weitzman, Fukushima, Nogeire, Roffwarg, Gallagher & Hellman (1971) Twenty-four hour pattern of the episodic secretion of cortisol in normal subjects. The Journal of Clinical Endocrinology & Metabolism, 33 (1), pp.14-22