Changes in Saliva Analytes Correlate with Horses’ Behavioural Reactions to An Acute Stressor: A Pilot Study

Abstract

Simple SummaryEmotionality is an individual characteristic defined as the propensity to respond to stress-inducing stimuli such as fear-inducing objects or social separation. Evaluation of emotionality in horses is important as it may impact their learning performance. Although emotionality is usually assessed by measuring behavioural patterns, biomarkers could provide additional information about stress response, especially with respect to its temporal dynamics. In this study, behavioural responses were measured as well as a panel of salivary biomarkers related to stress, including salivary alpha-amylase, lipase, total esterase, butyrylcholinesterase, adenosine deaminase, and cortisol, in riding horses after acute experimental stress (the sudden opening of an umbrella). We found significant changes in most of the salivary biomarkers evaluated after the induced stress, where increases in butyrylcholinesterase were more closely related to behavioural responses to acute stress and low salivary alpha-amylase values were more closely related to quietness behaviours. Therefore, this preliminary research provides information about the relationship between behaviour patterns and biomarkers of stress in saliva in horses, and opens the possibility of wider use of selected biomarkers in saliva, such as butyrylcholinesterase or alpha-amylase, for the evaluation of acute stress in horses.AbstractAcute stress induces an array of behavioural reactions in horses that vary between individuals. Attempts to relate behavioural patterns and physiological responses have not always given clear-cut results. Here, we measured the changes in a panel of salivary components: salivary alpha-amylase (sAA), lipase, total esterase (TEA), butyrylcholinesterase (BChE), adenosine deaminase (ADA), and cortisol, and their potential link with horses’ behaviours after acute stress. Saliva samples were collected in nine riding horses subjected to a test consisting of opening an umbrella. Saliva sampling was obtained at a basal time point in the stall (T1), in the test indoor arena (T2), at a time of stress (T3), and 30 min (T4) and 60 min (T5) later. The horses’ behaviour was recorded at T3 for 1 min. sAA, lipase, TEA, and BChE showed significant changes along time, increasing at T3 for BChE, and decreasing at T4 for sAA and BChE. Butyrylcholinesterase appeared to be the most reliable predictor of behavioural responses, as it correlated with the index of emotionality, of laterality, and the occurrence of alarm signals, while sAA decreased when horses expressed quieter behaviours. These first results bring promising lines for novel, more precise physiological markers of acute stress in horses that can bridge the gap between behaviour and physiology.

Changes in Salivary Analytes of Horses Due to Circadian Rhythm and Season: A Pilot Study

“…Notably, in the cases of cortisol, TEA, and BChE, the increases that occurred at certain times of the day reached the range of the values that were found in situations of acute stress or diseases [9]. This reinforces the need for saliva samples to be obtained during the same period of the day and/or season for comparative purposes.…”

“…Salivary cortisol levels increase in acute stress situations, such as road transport [3], intense exercise [4], or disease [5]. Moreover, some salivary stress biomarkers, such as total esterase (TEA), butyrylcholinesterase (BChE), and lipase (Lip) [6,7], as well as markers of cell-mediated immunity such as adenosine deaminase (ADA) [8], have been shown to be influenced by the sudden stress associated with fearfulness [9]. In addition, some other analytes, such as salivary alpha-amylase (sAA), γ-glutamyl transferase (gGT), creatine kinase (CK), urea, total bilirubin, total protein (TP), and phosphorus, increase in the saliva of horses with acute abdominal disease [10].…”

Changes in Saliva Analytes in Dairy Cows during Peripartum: A Pilot Study

“…Increases of the glucocorticoids and catecholamines around the time of calving by the hypothalamic–pituitary–adrenal axis and sympathetic nervous system (SNS) activation are associated with the delivery mechanisms [ 22 , 24 ] and could produce increases in cortisol and sAA [ 25 ]. BChE is also associated with the autonomic nervous system (ANS) in human beings [ 26 ] and increases in acute stress situations in pigs [ 27 , 28 ], sheep [ 11 ], and horses [ 12 ]. Salivary TEA, which also associated to the SNS activation [ 29 ], showed increases around thirteen days pre-calving and the day of calving, with median values similar to those reported in cows suffering lameness [ 4 ].…”

“…The salivary analytes evaluated in the chemistry profile were: Stress biomarkers. Salivary cortisol (sCor), salivary alpha-amylase (sAA), butyrylcholinesterase (BChE), total esterase (TEA), and lipase (Lip) [ 11 , 12 ]. Immunity biomarkers.…”

“…Stress biomarkers. Salivary cortisol (sCor), salivary alpha-amylase (sAA), butyrylcholinesterase (BChE), total esterase (TEA), and lipase (Lip) [ 11 , 12 ].…”