Testing individual variations of horses’ tactile reactivity: when, where, how?

Abstract

Tactile perception is involved in a variety of contexts (adaptations to climatic conditions, protection of the body against external dangers...) and is as important as the other sensory modalities for the survival of an individual.This tactile modality has been particularly well studied in humans, revealing high individual variations modulated by a variety of intrinsic and extrinsic factors such as age, sex, pathological disorders or temperament.Tactility is also involved in animals' social lives, although there are disparities between species. For example, social tactile contact among horses is limited, but this does not mean that they do not react to tactile stimuli but rather with their very thin skin they are able to detect minute stimuli (although they respond more to larger stimuli). Despite a fairly large effort to characterize it, there are controversies concerning equine tactile sensitivity.In this review, we examine studies that have used the same tool (Von Frey filaments) and try to disentangle what could explain the differences observed. It appears that many aspects are poorly known or controversial and that the procedures may be so different that the results of different studies cannot be compared. We went further by testing tactile reactivity of a population of unridden horses and found that four factors influenced their tactile reactivity (type of horse, filament size, body area, time of day). These results could explain some of the discrepancies observed in the literature and suggest, in particular, that more attention should be paid to the context of the test. Keywords: perception, equids, Von Frey filaments, methodology force. This principle therefore allows a known, measurable and reproducible force to be applied to the skin surface.Von Frey filaments were initially developed for humans to define tactile perception thresholds (Bell-Krotoski et al. 1995). A nylon filament delivering an average force of 0.07g was found to be a good predictor of the "normal" pressure threshold of light touch on hands and on a large part of the body of adult humans (Bell-Krotoski et al. 1995). This tool has become widely used both for human, i.e. medicine (Jerosch-Herold 2005) and preclinical neuroscience (Le Bars et al. 2001), often to assess pain with the hope of therapeutic translation (Mogil 2009) but also for animal (

Horses’ Tactile Reactivity Differs According to the Type of Work: The Example of Equine-Assisted Intervention

“…Tactile reactivity was estimated using von Frey filaments (Stoelting, IL, USA). These filaments consist of a hard-plastic body extended by nylon threads of variable thickness and are calibrated to apply a specific force on the skin, making it possible to obtain standardized measures [ 24 ]. When applying the tip of the filament perpendicularly against the skin, the application force increases as long as the experimenter continues the pressure, until the filament flexes and the filament is then removed.…”

“…Domestic horses constitute a very interesting model as there are clear individual differences in tactile reactivity that depend both on intrinsic and extrinsic factors [ 24 ]. Moreover, despite numerous tactile contacts with humans and materials during work, no specific study has been conducted on possible effects of working conditions on tactile reactivity [ 24 ].…”

“…Domestic horses constitute a very interesting model as there are clear individual differences in tactile reactivity that depend both on intrinsic and extrinsic factors [ 24 ]. Moreover, despite numerous tactile contacts with humans and materials during work, no specific study has been conducted on possible effects of working conditions on tactile reactivity [ 24 ]. Horses are particularly sensitive to skin stimulation, with the panniculus reflex, i.e., skin tremor, being triggered by a fly landing on the skin [ 25 ], and respond to the application of a standardized stimulus as light as 0.008 g [ 26 ].…”

“…In a recent literature review on horses’ tactile reactivity tested with the same calibrated tool (von Frey filaments), Gueguen et al [ 24 ] first showed that discrepancies between study procedures prevented definite conclusions on many possible factors of influence on tactile reactivity. Second, both intrinsic (e.g., sex, age, type of equid, welfare state) and extrinsic (e.g., living conditions) conditions were likely to have an influence on horses’ tactile reactivity.…”

“…We tested, using von Frey filaments as a consensual methodological tool to measure tactile reactivity, EAI and non-EAI horses, which, in order to diminish possible biases related to other factors, were in the same overall living conditions and tested in the same conditions (familiar location, same time of year, same weather) (see [ 24 ]). Finally, in order to have an idea of potential factors involved in tactile reactivity differences, we investigated spontaneous brushing procedures during grooming sessions of horses by adult humans presenting mental and/or developmental (e.g., autism) disorders and adults without any disorder (physical or mental) diagnosed.…”