*Back pain in horses can be related to psychological stress caused by aversive training * " (...) An additional source of back pain is emotional tension: according to Ridgway and Harman (1999), pain and psychological stress may induce an extension of the spine (“hollowing the back”) and an increased muscular tension at neck or back. Several authors also suggested that emotions are a possible source of back disorders (humans: Dionne et al., 2005; Houtman, Bongers, Smulders, & Kompier, 1994;
horses: Ridgway & Harman, 1999). Riding per se may be both a source of emotion (Schmidt, Aurich, Möstl, Müller, & Aurich, 2010) and of physical constraints, leading to a double potential effect on the emergence of back disorders (Hausberger et al., 2009, 2011). The type of training may also affect back tension through emotional impacts. Thus, in a training task where the horses had to learn to go backwards in response to a vocal order, the horses trained using a “classical” negative reinforcement (stopping of a mild agitation of a whip in front of the horse when the response is obtained, Skinner, 1938) went backwards with a high and hollow neck, which may induce an increase of vertebral constraints (see Waldern et al., 2009) whereas those trained using a positive reinforcement (food reward as soon as the horse gave the appropriate response, Skinner, 1938) were observed more with a round neck (Sankey et al.,
2010). Steady head carriages and roundness (here related to the use of a positive reinforcement) reflect calmness and spine welfare (Egenwall et al., 2012; von Borstel et al., 2009; Waldern et al., 2009; WarreSmith & McGreevy, 2007). The observed prevalence of negative reinforcement and punishment in the
current education of horses (Warren-Smith & McGreevy, 2007) might lead to repeated undesired postures that might become chronic and hence a source of back disorders, even outside of work."
-✍️ Lesimple C., Fureix C., Aubé L., Hausberger M., (2016). Detecting and measuring back disorders in nonverbal individuals: The example of domestic horses. Animal Behavior and Cognition 3 (3), 159-179 - 5 minutes ago