Overnight dexamethasone suppression and cortisol index tests in clinically healthy horses and with crib-biting.

The research paper investigates whether crib-biting behavior in horses impacts their hypothalamic-pituitary-adrenal axis functionality, as gauged by dexamethasone suppression and cortisol index tests. However, the results revealed these tests alone couldn’t differentiate between crib-biting and non-crib-biting horses, signaling a need for more precise techniques.

Research Objective

• The main objective of the research was to investigate the functionality of the hypothalamic-pituitary-adrenal axis in healthy horses exhibiting crib-biting behavior.
• The researchers sought to achieve this by using the dexamethasone suppression test (DST) and the cortisol index (CI) and evaluating the rhythmicity of the circadian cycle of cortisol in these horses.

Methods

• The study involved 20 Colombian Creole horses divided into two groups: crib-biting horses (10) and non-crib-biting horses (10). The horses lived under similar management conditions.
• Blood samples were taken twice a day (morning and afternoon) from each horse to determine the cortisol index (CI). The DST protocol was initiated after the afternoon collection.
• The serum cortisol concentration was determined by sandwich ELISA (enzyme-linked immunosorbent assay) at every stipulated time and post-treatment with dexamethasone for both groups.

Results

• Results showed that serum cortisol concentrations were equal in both groups. There was also no significant difference in the cortisol index (CI) between the two groups.
• DST showed positive results in all horses, irrespective of their crib-biting or non-crib-biting status.

Conclusions

• The study concluded that both the DST and CI tests could not differentiate between crib-biting and non-crib-biting horses.
• The researchers recommended implementing more precise techniques in future studies to better differentiate between the two conditions.
• They also suggested that longitudinal studies should be carried out to establish specific reference values and cutoff points for interpreting cortisol suppression in crib-biting cases.
• To gain more comprehensive insights, they proposed including other hormones such as adrenocorticotropic hormone and corticotropin-releasing hormone in the studies due to their multifactorial nature and high variability in cortisol values.