Horses’ perception of a threat posed by sounds of different origin

Abstract

The aim of the study was to assess the behavioural reaction and emotional arousal of warmblood horses in response to sounds of different origin, and to classify those sounds into neutral ones, those causing a behavioural change and those causing a behavioural and physiological stress response. We tested the hypothesis that the perception of a sound as neutral or potentially threatening does not simply depend on the sound origin per se, but rather on the context in which the sound occurrs (predictability), additionally enhanced by the novelty effect. Recordings of 40 sounds, known (KS) and unknown (US), from four groups: anthropogenic (AS), neutral animal (NAS), predator (PS), and inanimate environment sounds (IES), were played to 20 warmblood horses remaining in their familiar paddock. The duration, frequency or occurrence of certain behaviours (e.g. walking, feeding, standing alert, stopping current activity), the heart rate (HR) and heart rate variability (HRV) were measured. The horses’ reactions were rather weak and short-term. Most of the sounds resulted in distraction (increase in alertness). The horses ate less, walked and stood alert longer, and had a higher HR after certain sounds were played. The strongest stress response (physiological and behavioural) to NAS, mostly US, was observed. PS caused behavioural disturbance, but no cardiac activity changes. The weakest responses were observed for AS and IES. Modern, stable-kept horses remain vigilant to auditory stimuli in their environment and differentiate their responses to different sounds. The perception of a threat posed by sounds depends on their unpredictability and novelty.

Can Sound Alone Act as a Virtual Barrier for Horses? A Preliminary Study

“…These circumstances had an impact on HRV changes, but the response was delayed. Another reason for these differences may be the measurement time—5 min in the previous [ 31 ] and 1 min in the current study.…”

“…HRV reflects the modulating effect of ANS on cardiac responses [ 37 ]. In the previous study [ 31 ], we showed that a 1-min recording was not sufficient to influence HRV responses (RMSSD, LF, HF, LF/HF), and mainly only HR and RR changes were noted. In that particular case, horses were in the known paddock in a group and were not supposed to border a line.…”

“…However, according to the risk-disturbance hypothesis [ 30 ], animal reactions towards different frightening stimuli may derive from a generalised antipredator defence mechanism. In the previous study [ 31 ], we observed that horses responded mostly to the sounds of unusual animals, like pigs or chimpanzees, and not to the vocalisation of predators. Rochais and Hausberger [ 32 ] also noted that novelty and unexpectedness provide the distraction potential of the sounds.…”

“…The sound was violent and novel for subjects and was played at a sound intensity level (LA) of approximately 80 dB measured at a distance of 1 m from the loudspeaker to provide its acute alarming features [ 12 , 13 ]. This intensity has been proven to have only a short-term effect on the cardiac response [ 31 ]. If the horse reached the finish line before the end of the recording time, the recording was stopped.…”

Does social motivation mitigate fear caused by a sudden sound in horses?

“…Two different sounds were used during these tests: sound A (squeal of a pig, produced during distress (Çavuşoğlu et al 2020 )) and sound B (futuristic characteristics; similarity to radio and TV interference, crackling). The sounds were selected based on the results of our previous studies: comparing reaction to 40 sounds of different origin (Janicka et al 2022a ), assessing the possibility to use sound stimulus in creating virtual barrier (Janicka et al 2022b ) and comparing reactions to 40 known and four novel sounds (unpublished data). Sounds that were chosen elicited similar and strongest avoidance behaviour.…”