Detecting and Measuring Back Disorders in Nonverbal Individuals: The Example of Domestic Horses

Abstract

-Back disorders are amongst the major health-related disorders associated to working conditions in our society. Horses share with humans the exposure to potential physically harmful working conditions leading to back disorders. However, despite their high prevalence, these problems are often unacknowledged in the horse industry, mostly because their diagnosis remains difficult, particularly in field conditions. In the present review, we review the current scientific knowledge on back vertebral, muscular and musculoskeletal disorders. We will first present the existing knowledge about their prevalence and the tools available for diagnosis. Then, the different potential sources of back pain, including anatomical implications, the effect of emotionality and working conditions will be discussed. We finally present the existing behavioral, postural and physiological indicators of back pain that could help an early detection of back disorders.Keywords -Horse, Equine, Work, Illness, Back disorder assessment, IndicatorsSickness is defined as a state of unwellness, distress or disgust (Oxford Guide of the English Language, 1984), combining physical and emotional disorders. Sickness induces aversive experiences that range from mild discomfort to acute pain, which are mechanisms preventing the organism from incurring injuries (Bateson, 1991). According to this definition, the term "sickness" fits very well with back disorders. In humans, the presence of back disorders is related to increased aggressiveness (Berkowitz, 1993) and/or depression (Curie & Wang, 2004;Garon & Leavitt, 1983) and lower back pain is amongst the main causes of sick leave (Dionne et al., 2005). Back disorders may be caused by strictly physical parameters, such as bony dysfunction or malformations. However, working conditions are more and more often identified as a major source of back pain in humans (Banibrata, 2014;Widanarko, Legg, Devereux, & Stevenson, 2014), related to postural or psychological constraints.In horses too, physical malfunctions and malformations are possibly involved in some back related disorders (Haussler, 1996;Stubbs et al., 2006). However, working conditions, have also been proposed as further sources of such disorders (Fonseca et al., 2006;Gillis, 1999;Haussler, 1997;Jeffcott, 1980): horses share with humans working activities that may cause psychological (e.g., suppression of emotions) and physical stress (e.g., physical constraints; McGreevy & McLean, 2005). In this review, we present the current knowledge about the prevalence of back disorders and the tools used to diagnose them. We will review the potential causes of back disorders with a special highlight on working conditions. Psychological, physical and anatomical impacts of riding will be discussed in relation to the presence of visible indicators of back disorders. Finally, as the presence of back disorders is one of the main Lesimple et al. 160 pathologies in horses, we will review the validated indicators of back disorders as well as the signals that are ...

Indicators of Horse Welfare: State-of-the-Art

“…Evaluations of back pain/vertebral disorders presented a strong agreement between practitioners regardless of their occupational background (e.g., [38,40,77]), as well as between methods [38]. Although muscular activity cannot be estimated by simple visual examination, its evaluation constitutes a reliable indicator of horses' welfare [39].…”

“…The values of these angles were significantly correlated to the prevalence of vertebral disorders: the hollower the neck, the more the spine was affected. On the contrary, horses with a rounded neck had no vertebral disorders [38,39].…”

“…Changes in welfare state, either in a positive or in a negative way, can affect the physiology of an individual, but physiological signals of welfare are difficult to apprehend in a chronic perspective as: (1) it can take a long time before a modification of the environment is reflected by physiological parameters (i.e., blood count), it is difficult to know for sure what environmental conditions are effective, and (2) short-term internal changes (e.g., hormonal) can reflect chronic as well as acute situations. However, the presence of chronic vertebral disorders, related to lameness [71][72][73], changes in gait [71,72] or asymmetry of the pelvic bony prominences [72,74], is commonly considered as one of the most widespread causes of impairment of working horses' welfare [39,72,[74][75][76] and can induce muscular hypertonicity along the spine that can be assessed by manual palpation [36,38,40,76,77]) or static electromyography (sEMG) [38]. Evaluations of back pain/vertebral disorders presented a strong agreement between practitioners regardless of their occupational background (e.g., [38,40,77]), as well as between methods [38].…”

Low plasma cortisol and fecal cortisol metabolite measures as indicators of compromised welfare in domestic horses (Equus caballus)

“…In horses, backward ear position is commonly associated with negative emotional states, such as pain or a negative cognitive bias [ 34 , 67 , 68 ]; or during agonistic interactions [ 69 ]. Ear position for each horse was noted at 15 minute intervals and on two different rest days until 10 ear positions were obtained per horse according to the method used by Lesimple et al [ 42 , 43 ]. Three positions were defined in accordance with previous studies on sheep and horses [ 67 , 70 ]: axial (perpendicular to the head—rump axis), forward (tip of the ear towards the front at an angle of more than 30° from the perpendicular) or backward (tip of the ear towards the back at more than 30° from the perpendicular).…”

On-Farm Welfare Assessment of Horses: The Risks of Putting the Cart before the Horse

“…Some other aspects, such as the indicators chosen, would require further descriptions and thought. For example, using the neck shape for assessing body condition, as done in some studies (e.g., [29]) using this protocol, may be misleading, as a hollow neck may be due to working conditions more than actual body condition [41,42]. « Unresponsiveness », « apathy » and « depression » would deserve to be redefined in view of recent reports that describe these terms with more objective criteria (e.g., time without absence of movement, eye blinking [40]).…”