Assessment of the welfare of the police horses based on salivary cortisol levels during the special search operations

Salivary cortisol is a reliable, non-invasive biomarker for assessing acute stress in both humans and animals. This study investigates whether service horses experience significant stress during search operations by analyzing salivary cortisol levels in relation to circadian rhythms. A central concern is the potential mismatch between observed welfare and physiological stress indicators, as horses may appear outwardly calm while experiencing internal stress. To address this, cortisol samples were collected at different times of day to capture natural hormonal fluctuations. The study aimed to establish individual circadian cortisol curves over the course of a year, particularly during training periods. A comparative model was also developed to determine whether the horses exhibited stress responses, based on deviations from individual baseline values. The hypothesis posits that each horse has a unique basal cortisol level. Understanding these variations is vital for identifying stress patterns that may not be evident through behavior alone and for improving welfare monitoring in working horses. The objective of this study was to ascertain the extent of variability in salivary cortisol levels in working horses with respect to their welfare. A total of 21 horses were enrolled in the study, and 240 experimental saliva samples were collected from each horse to determine the variability of cortisol levels during retrieval events. Samples were collected at five points: before outbound transport, upon arrival, during the training, before inbound transport (i.e. at the end of the training), and after back to the barn. Concurrently, saliva samples were collected over the course of the year to ascertain the circadian rhythm of cortisol. The results indicated that salivary cortisol concentrations were near circadian values during periods of exercise yet were significantly elevated above these circadian concentrations during periods of transportation. Therefore, transport distances were divided into groups for the purpose of comparison. The results demonstrated that cortisol concentration generally increased before and after transport at shorter distances. It is evident that, over longer distances, a decrease in performance is observed, which is indicative of adaptation. The study thus concludes that cortisol levels decrease throughout the exercise, and that these levels return to their circadian rhythm. This indicates that the horse is not experiencing exercise stress. • Salivary cortisol is a reliable, non-invasive biomarker for assessing acute stress in mounted police horses. • The circadian cortisol values were then compared with cortisol levels obtained during search operations and transport. • The concept of a "stress factor" was introduced to denote the extent to which the instantaneous cortisol value exceeds the circadian value. • The absolute stress factor values indicate that cortisol levels during training approximate the circadian values. • Adaptation to stress and a decrease in salivary levels were observed during transport of horses exceeding 145 km.