Cortisol Levels in Stressed Shelter Dogs
Workers at pet shelters work tirelessly to provide a temporary home for pets in their care, but despite those best efforts, shelter pets face multiple stressors that can decrease their quality of life. Exposure to chronic stress may cause long-term medical and behavioral problems in shelter dogs, and evaluating their stress levels is necessary to improve their welfare. A recent study performed by researchers at Utrecht University in the Netherlands investigated hormone cortisol levels in shelter dogs’ hair before, during, and after their stay in a shelter to evaluate how significantly they were affected by the experience.
Measuring cortisol levels
Cortisol is synthesized in the adrenal cortex in response to stress-induced hypothalamic-pituitary-adrenal (HPA) axis activation. Saliva, blood, and urine cortisol levels reflect immediate, real-time levels, while cortisol levels in hair quantify systemic cortisol exposure over extended periods. The exact mechanism for depositing cortisol in hair is not fully understood, but hair evaluation in human and veterinary medicine has been a reliable biomarker for evaluating exposure to long-term stressors. Collecting saliva, blood, and urine samples every few hours is not feasible to evaluate stress in shelter dogs, whereas measuring hair cortisol levels can easily and non-invasively measure the dogs’ long-term stress responses. The Utrecht study researchers’ aims included:
- Comparing hair cortisol concentration (HCC) levels in shelter dogs when they were relinquished, during the shelter period, and after adoption
- Comparing HCC levels in pre-shelter dogs and control pet dogs
- Evaluating the relationship between HCC and urinary cortisol levels in the same dogs at the shelter and after adoption
Study parameters
The study included 52 dogs admitted to the largest Netherlands shelter between October 2018 and August 2019. Dogs who had a physical health condition, high anxiety, or aggressive behavior, and those younger than 1 year or older than 13 years of age were excluded. The dogs stayed in the shelter from five days to eight months, but most stayed at least two weeks. They were housed in glass-fronted indoor kennels that had a bar-fronted outdoor enclosure. The control group included 20 pet dogs who stayed in their regular home environment.
Hair samples were taken by shaving the hair to the skin, unless the razor scared the dog when scissors were used to prevent a fear response. Wool and guard hair was used for analysis. The shelter dogs’ samples were collected from the same area immediately after intake, six weeks after intake, six weeks after adoption, and six months after adoption, whereas hair samples from control pets were collected once. Urine samples from shelter dogs were collected on days 1, 2, 3, 7, and 12 while in the shelter and after adoption.
Data processing
The hair samples were washed twice with isopropanol and dried in a 37-degree Celsius oven. An enzyme-linked immunoassay (ELISA) cortisol determination kit was used according to the manufacturer’s specifications, and samples were run in duplicate. Results were measured as cortisol concentration in pg of cortisol per mg of hair sample. The urine cortisol to creatinine ratio (UCCR) was determined for the shelter dogs while in the shelter and post-adoption.
Results
This study compared HCC levels in shelter dogs at multiple time points before, during, and after they stayed in the shelter, and also compared HCC levels in pre-shelter control pet dogs. Results included:
- Dogs had a higher HCC while in the shelter — HCC levels were significantly higher in the samples taken six weeks after intake than in samples taken at intake, and six weeks and six months after adoption.
- Dogs at intake did not appear stressed — HCC levels were similar in samples taken from dogs at intake and in the control pet dogs, indicating these dogs were not stressed.
- HCC correlated to UCCR — The HCC was moderately but significantly correlated to UCCR, demonstrating a definite relationship between the two measures.
- Smaller dogs had higher HCC — HCC levels were higher in small shelter dogs compared with larger dogs. In previous studies, saliva UCCR and cortisol levels were also higher in small dogs compared with large- and giant-breed dogs.
- Female dogs had higher HCC — Female dogs had a higher HCC compared with males, and females had a higher behavioral and HPA-axis stress response. Circulating estradiol levels have been shown to cause a higher HPA-axis response in female rodents and humans, which could explain the latter finding. Previous studies have shown higher HCC levels in female herding dogs, solitary hunting breeds, and hunting village dogs.
- Stray dogs had a lower HCC — Stray dogs had a lower HCC than relinquished dogs, indicating that a dog’s previous life experience could affect their ability to adjust to a shelter environment.
- Melanin type did not seem to affect HCC — Previous studies have indicated that hair color could play a role in cortisol concentration, but this study did not support that finding.
Overall, this study demonstrated that monitoring HCC levels in shelter dogs are a non-invasive, effective way to learn about their stress levels, and to hopefully find ways to improve their health and wellbeing.
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