The horse’s role throughout history, first as a meat animal and then a working animal, initially established their place as a “tool” to meet human needs. In more recent times, the horse’s primary role has shifted to that of an athlete and companion, participating in racing and a wide variety of sports and leisure pursuits.

This current role has resulted in horses less commonly being referred to as livestock or farm animals, and more frequently being referred to as companion animals [1,2]. Even with this more modern classification, welfare concerns remain. Horse welfare has received less attention than farmed livestock [1], and their role as a ridden animal exposes them to specific welfare concerns that do not apply to other companion animals [1,3,4]. Perceptions regarding the impact of factors that affect horse welfare vary between non-horse owners, horse owners, and competitors, and even vary depending on the discipline in which an individual competes [5,6], suggesting that the “working” role of horses may influence decisions about care and welfare.

Most horse owners and caregivers want the best for the horses in their care, despite this, many of the decisions about housing, handling, care, and training are not welfare-oriented [7,8,9,10,11]. Decisions relating to horse handling and care are frequently based on the personal established beliefs of owners, trainers, and caregivers, often influenced by information passed to them from previous generations of horse trainers [8]. The specific equestrian sector a person aligns with may also influence their beliefs about exactly what constitutes appropriate care and welfare [5].

Even though humans have a lengthy and close history with horses, there are frequent gaps in the owner’s/trainer’s/caregiver’s understanding of ethology, horse behaviour, and indicators of welfare [7,8,12,13,14,15,16,17]. The science behind how animals learn, how they perceive the world around them, and the way they respond to that information, is poorly understood by many amateurs and professionals who work with horses [8,12,16,18,19,20,21]. In instances where an owner/trainer/caregiver does have appropriate theoretical knowledge, it still does not always translate into practical application [8,11]. In one survey, most respondents identified that individual housing is a welfare concern for horses, and yet many respondents in the same survey housed their horses individually [11].

Whilst owners, riders, trainers, and caregivers frequently describe how important the relationship is between a horse and their human, the human–animal interactions (HAIs) provided are often negative experiences for the horse, with many common handling and training techniques focusing on achieving the human’s goal at the time, with limited consideration of the horse’s emotional experience [22,23]. Negative reinforcement and punishment-based approaches are common in horse training and handling, with the goal being to generate behaviours that the human desires, with little true choice to the horse, and limited reward for participation other than the relief from, or avoidance of, an aversive stimulus [11,12].

Horses are large animals with quick reactions. They are neophobic and claustrophobic, and remain acutely aware of their surroundings [22,45,46,47,48]; these traits can have a significant impact when being asked to participate in a HAI or HVP for which they have not been adequately prepared.

As a prey species, horses rely on flight where possible as a primary method of survival. When faced with novel situations, physical or psychological pressure, or real or perceived restraint, fear responses will typically be activated. The observable responses may be active, manifesting as avoidance or escape behaviours, or defence behaviours (threat or attack); or passive, manifesting as immobility (freezing) or displacement behaviours. The behaviours exhibited are influenced by an individual’s coping strategy; the coping style may be either more proactive or more reactive and will remain constant across time and contexts [49]. Attempts to exert control over a situation through the performance of defensive behaviours, or efforts to flee from a stressor, are characteristic of a more proactive strategy, whereas reduced responsiveness, emotional blunting and freezing are characteristic of a more reactive strategy [49,50].

When compared to a horse displaying volatile behavioural responses, a horse displaying reduced behaviours during a HVP may seem preferential; however, this is not always the case. Despite the reduced behavioural response, reactive coping styles are linked with a more pronounced physiological response to stress [49,50]. Hence, even when a horse appears calm and compliant, there may still be concerns for the horse’s emotional well-being [14,49,51]. It should also be remembered that horses displaying behaviours associated with reactive coping strategies may remain immobile until they reach a threshold, and then may suddenly react in a large and volatile way [50]. This sudden performance of volatile behaviours from a horse that previously appeared calm and compliant is sometimes misinterpreted as a horse being ‘unpredictable’ [50].

The responses that are most dangerous to humans occur when a horse feels the need to avoid, escape, or defend itself from perceived threat. The specific behaviours that may result in injury to the human handler in these scenarios include biting, kicking, striking, rearing, running/trampling/barging, or moving in a way that crushes the human between the horse and another object. These behaviours may be exhibited immediately at the commencement of a HAI or HVP, or the horse may display these behaviours at some point during the HAI or HVP as a result of the prolonged exposure to a stressor or the cumulative effect of being exposed to multiple different stressors over a period of time [50,52].

Actions that are undertaken by humans during a HAI or HVP can significantly impact a horse’s behaviour during future HAIs and HVPs [53]. Continuing to expose the horse to a perceived aversive stimulus past that individual’s reaction threshold; provoking a fear response; reinforcement of an undesirable behaviour; poorly timed reinforcement; and/or the use of punishment, particularly noncontingent punishment, can all play a role in creating unwanted responses in future HAI and HVPs [52,53,54,55].

It is important to remember though that many of the behaviours that pose safety concerns to humans during a HAI or HVP are entirely natural behaviours in the horse [56].