Date Published: May 22, 2019
Publisher: Public Library of Science
Author(s): Rowena M. A. Packer, Alexander M. Davies, Holger A. Volk, Holly L. Puckett, Sarah L. Hobbs, Robert C. Fowkes, Giuseppe Biagini.
Hair is an emerging biological matrix in which to measure chronic HPA axis activity, offering a longer term view into an animal’s life. We explored effects of exogenous (e.g. lifestyle, medications, social environment) and endogenous (e.g. disease, behaviour) stressors on hair cortisol concentration (HCC) in a population of Border Collies (BCs). Owners of BCs were recruited and reported their dog’s lifestyle, clinical history, anxiety-related behaviour, and collected a white hair sample from their dog’s dorsal neck region. HCC was determined using established methods with a commercial cortisol assay kit. Samples from 135 BCs were analysed, with 91 healthy controls and 44 diagnosed with epilepsy as a model disease. Factors associated with higher HCC included psychosocial stressors (living with three or more other dogs) and lifestyle (engaging in competitive flyball); while factors associated with lower HCC included anxiety (stranger-directed and non-social), health (epilepsy diagnosis, with number of seizures to date negatively correlated with HCC) and medication (certain anti-epileptic drugs were associated with elevated or reduced HCC). These novel results highlight the potential of chronic stress with frequent or persisting HPA-axis hyperactivity leading to a state of hypocortisolism, and the need to consider stressor recency and recurrence when interpreting HCC data.
The domestic dog is a species of global importance, with an estimated 10.5 million kept as companion animals in the UK alone . Other key canine roles include military and police dogs, assistance dogs for a variety of medical conditions, with the dog also considered as a model for many heritable human diseases . The welfare of dogs in all of these roles is of societal interest, and quantifying their stress levels has been a topic of scientific interest over the past half a century. Stressors may be actual or perceived, and can be psychological or physiological in origin . Stress in dogs is commonly studied using behavioural observations in combination with measurement of cortisol, an endogenous glucocorticoid hormone found in biological matrices including blood, urine and faeces, to quantify hypothalamic-pituitary-adrenal axis (HPA) activity. A multitude of endogenous and exogenous stressors have been identified to alter cortisol levels in dogs including unpredictable aversive stressors (e.g. sound blasts, electric shocks and falling bags , working , hunting , thunderstorms , and dog park visits ). Understanding the effects of potential stressors on stress physiology in dogs is vital for evidence-based optimization of their care, particularly where stressors are modifiable or preventable.
To our knowledge this is the largest and most in-depth single-breed study of the effects of endogenous and exogenous stressors on HCC in the domestic dog. The results highlight complex effects of stressors on the HPA axis, including the social environment, leisure activities, disease, medication, and behavioural problems, with both up and downregulation of the HPA axis observed. These data corroborate the results of previous investigations into HCC into dogs, including potentially negative effects of a large number of social companions in the home  and involvement in competitive sports , while identifying novel effects on the impact of anxiety and chronic neurological disease on HCC.
Hair cortisol is a promising measure of chronic stress in dogs, influenced by both endogenous and exogenous stressors, including behaviour, disease, medication, lifestyle and the social environment. Stressors may cause both up or down regulation of HCC and thus caution should be taken in interpreting results, with characteristics of the stressor considered including recency and recurrence. HCC may provide new insights to support or challenge mechanistic notions of chronic stress responses in dogs, and highlights the need to expand this body of research in dogs.