BackgroundRecent reviews question current animal models of depression and emphasise the need for ethological models of mood disorders based on animals living under natural conditions. Domestic horses encounter chronic stress, including potential stress at work, which can induce behavioural disorders (e.g. “apathy”). Our pioneering study evaluated the potential of domestic horses in their usual environment to become an ethological model of depression by testing this models’ face validity (i.e. behavioural similarity with descriptions of human depressive states).Methodology/Principal FindingsWe observed the spontaneous behaviour of 59 working horses in their home environment, focusing on immobility bouts of apparent unresponsiveness when horses displayed an atypical posture (termed withdrawn hereafter), evaluated their responsiveness to their environment and their anxiety levels, and analysed cortisol levels. Twenty-four percent of the horses presented the withdrawn posture, also characterized by gaze, head and ears fixity, a profile that suggests a spontaneous expression of “behavioural despair”. When compared with control “non-withdrawn” horses from the same stable, withdrawn horses appeared more indifferent to environmental stimuli in their home environment but reacted more emotionally in more challenging situations. They exhibited lower plasma cortisol levels. Withdrawn horses all belonged to the same breed and females were over-represented.Conclusions/SignificanceHorse might be a useful potential candidate for an animal model of depression. Face validity of this model appeared good, and potential genetic input and high prevalence of these disorders in females add to the convergence. At a time when current animal models of depression are questioned and the need for novel models is expressed, this study suggests that novel models and biomarkers could emerge from ethological approaches in home environments.

This study aimed to determine whether horses have a kind of memory of humans (based on previous interactions), leading to a general significance of humans revealed by their reactions to humans in subsequent interactions. Subjects were 59 adult horses used to interact daily with humans. Three types of behavioural tests involving an unknown experimenter evaluated three possibly different memorized types of human-animal interactions (not work-related, using work-related objects, unfamiliar working task). We also performed standardized observations of routine interactions between each horse and its familiar handler (caretaker). To get a broad overview of the horses' reactions to humans, we recorded both investigative and aggressive behaviours during the tests, representing respectively a "positive" and a "negative" memory of the relationship. Whereas correlations between tests revealed a general perception of humans as either positive or negative, unusual tests, i.e. that are not usually performed, elicited more positive reactions. Moreover, some horses reacted positively to a motionless person in their box, but negatively when this same person approached them, for example for halter fitting. Overall, aggressive reactions were more reliable indicators of the relationship than positive reactions, both between tests and between familiar and unfamiliar humans. Our results also show generalization of the perception of humans. These results support our hypothesis that perception of humans by horses may be based on experience, i.e. repeated interactions. Altogether, our results support the hypothesis that horses can form a memory of humans that impacts their reactions in subsequent interactions.

Postures have long been used and proved useful to describe animals’ behaviours and emotional states, but remains difficult to assess objectively in field conditions. A recent study performed on horses using geometric morphometrics revealed important postural differences between 2 horse populations differing in management conditions (leisure horses living in social groups used for occasional “relaxed” riding/riding school horses living in individual boxes used in daily riding lessons with more constraining techniques). It was suggested that these postural differences may reflect chronic effects of riding techniques on the horses’ kinematics and muscular development. In the present study, we tried to evaluate the interest of postural measures to assess welfare in horses. This study was separated into 2 parts. First, 18 horses coming from these 2 types of populations (leisure/riding school horses) were submitted to 2 back evaluations by 1) manual examination (experienced practitioner) and 2) sEMG measures along the spine. We then measured neck roundness on 16 of these 18 horses. The results highlighted high correlations between manual and sEMG examinations over the spine. sEMG measures at the different locations were strongly correlated all over the spine. Moreover, neck postures and muscular activities were strongly correlated, horses with concave necks having higher sEMG measures both at precise locations (i.e. cervical sites) but also when comparing neck postures to the whole spine muscular activity highlighting the functioning of horses’ back as a whole. Lastly, strong differences appeared between the populations, leisure horses being evaluated as having sounder spines, exhibiting lower sEMG measures and rounder neck than the riding school horses. sEMG measures and neck “roundness” seemed therefore to be reliable indicators of back disorders, easy to evaluate in field conditions. This highlights the accuracy of using postural elements to evaluate the animals’ general state and has important implications for animals’ welfare evaluations.

A central question in the interspecific human/animal relationship is how domestic animals perceive humans as a significant element of their environment. In this study, we tested the hypothesis that the use of positive or negative reinforcement in horse training may have consequences on the animals' perception of humans, as a positive, negative or neutral element. Two groups of ponies were trained to walk backwards in response to a vocal order using either positive or negative reinforcement. Heart rate monitors and behavioural observations were used to assess the animals' perception of humans on the short (just after training) and long (5 months later) terms. The results showed that the type of reinforcement had a major effect on the subsequent animals' perception of familiar and unfamiliar humans. Negative reinforcement was rapidly associated with an increased emotional state, as revealed by heart rate measurements and behavioural observations (head movements and ears laid back position). Its use led the ponies to seek less contact with humans. On the contrary, ponies trained with positive reinforcement showed an increased interest in humans and sought contact after training. This is especially remarkable as it was reached in a maximum of 5 sessions of 1 to 3 min (i.e. 5 to 15 min) and had lasting effects (visible after 5 months). Even learning was positively influenced by positive reinforcement. Overall, horses seem capable of associating humans to particular experiences and display extended long-term memory abilities.

BackgroundExperiencing acute pain can affect the social behaviour of both humans and animals and can increase the risk that they exhibit aggressive or violent behaviour. However, studies have focused mainly on the impact of acute rather than chronic painful experiences. As recent results suggest that chronic pain or chronic discomfort could increase aggressiveness in humans and other mammals, we tested here the hypothesis that, in horses, aggression towards humans (a common source of accidents for professionals) could be linked to regularly reported vertebral problems of riding horses.Methodology/Principal FindingsVertebral examination and standardized behavioural tests were made independently on the same horses. Here we showed that most horses severely affected by vertebral problems were prone to react aggressively towards humans (33/43 horses, chi-square test, df = 1, χ2 = 12.30, p<0.001), which was not the case for unaffected or slightly affected horses (9/16 horses, chi-square test, df = 1, χ2 = 0.25, p>0.05). The more affected they were, the fewer positive reactions they exhibited (rs = −0.31, p = 0.02).Conclusions/SignificanceThis is to our knowledge the first experimental evidence of such a link between chronic discomfort/potential pain (inferred from the presence of vertebral problems) and aggression, suggesting that chronic painful experiences may act in ways similar to those of acute experiences. Chronic discomfort or pain may often be overlooked when facing “bad tempered” individuals, whether humans or animals. This experimental study confirms the importance of including chronic discomfort or pain as a major factor in interpersonal relations and models of aggression.

BackgroundBack pain is the cause of bad welfare in humans and animals. Although vertebral problems are regularly reported on riding horses, these problems are not always identified nor noticed enough to prevent these horses to be used for work.Methodology/Principal FindingsNineteen horses from two riding centres were submitted to chiropractic examinations performed by an experienced chiropractor and both horses' and riders' postures were observed during a riding lesson. The results show that 74% of horses were severely affected by vertebral problems, while only 26% were mildly or not affected. The degree of vertebral problems identified at rest was statistically correlated with horses' attitudes at work (neck height and curve), and horses' attitudes at work were clearly correlated with riders' positions. Clear differences appeared between schools concerning both riders' and horses' postures, and the analysis of the teachers' speech content and duration highlighted differences in the attention devoted to the riders' position.Conclusion/SignificanceThese findings are to our knowledge the first to underline the impact of riding on horses' back problems and the importance of teaching proper balance to beginner riders in order to increase animals' welfare.

Captive / domestic animals are often described as inactive, with the implicit or explicit implication that this high level of inactivity is a welfare problem. Conversely, not being inactive enough may also indicate or cause poor welfare. In humans, too much inactivity can certainly be associated with either negative or positive affective states. In non-human animals, however, the affective states associated with elevated or suppressed levels of inactivity are still not well understood. Part of the complexity is due to the fact that there are many different forms of inactivity, each likely associated with very different affective states. This paper has two aims. One is to identify specific forms of inactivity that can be used as indicators of specific affective states in animals. The other is to identify issues that need to be resolved before we could validly use the remaining, not yet validated forms of inactivity as indicators of affective state. We briefly discuss how inactivity is defined and assessed in the literature, and then how inactivity in its various forms relates to affective (either negative or positive) states in animals, basing our reasoning on linguistic reports of affective states collected from humans displaying inactivity phenotypically similar to that displayed by animals in similar situations, and, when possible, on pharmacological validation. Specific forms of inactivity expressed in response to perceived threats (freezing, tonic immobility, and hiding) appear to be, to date, the best-validated indicators of specific affective states in animals. We also identify a number of specific forms of inactivity likely to reflect either negative (associated with ill-heath, boredom-like, and depression-like conditions), or positive states (e.g. 'sunbasking', post-consummatory inactivity), although further research is warranted before we could use those forms as indicators of the affective states. We further discuss the relationship between increased inactivity and affective states by presenting misleading situations likely to yield wrong conclusions. We conclude that more attention should be paid to inactivity in animal welfare studies: specific forms of inactivity identified in this paper are, or have the potential to be, useful indicators of affective (welfare) states in animals. Other specific forms are likely to be linked with either negative or positive states. What can inactivity (in its variousWe propose further research directions to further validate those forms of inactivity. Captive / domestic animals are often described as inactive, with the implicit or explicit 16 implication that this high level of inactivity is a welfare problem. Conversely, not being 17 inactive enough may also indicate or cause poor welfare. In humans, too much inactivity can 18 certainly be associated with either negative or positive affective states. In non-human 19 animals, however, the affective states associated with elevated or suppressed levels of 20 inactivity are still not well understood. 21Part of ...

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms 1 Exploring aggression regulation in managed groups of horses Equus caballusAbstract. Horses are highly social animals that have evolved to live in social groups.However, in modern husbandry systems, single housing prevails where horses experience social isolation, a challenge-to-welfare factor. One major reason for this single housing is the owners' concerns that horses may injure each other during aggressive encounters. However, in natural conditions, serious injuries due to aggressive encounters are rare. What could therefore explain the claimed risks of group living for domestic horses? Basing our questioning on the current knowledge of the social life of horses in natural conditions, we review different practices that may lead to higher levels of aggression in horses and propose practical solutions.Observations of natural and feral horses mostly indicate a predominance of low frequencies and mild forms of aggression, based on subtle communication signals and ritualized displays and made possible by group stability (i.e. stable composition), dominance hierarchy and learning of appropriate social skills by young horses. Obviously, adults play a major role here in canalizing undesirable behaviours, and social experience during development, associated with a diversity of social partners, seems to be a prerequisite for the young horse to become socially skilled.Given the natural propensity of horses to have a regulation of aggression in groups, the tendency to display more aggression in groups of domestic horses under some management practices seems clearly related to the conditions offered. We therefore review the managing practices that could trigger aggressiveness in horses. Non social practices (space, resource availability) and social practices (group size, stability of membership, composition and opportunities for social experiences during development) in groups of domestic horses are discussed here.2 Finally, we propose simple practical solutions leading to more peaceful interactions in groups of domestic horses, based on the knowledge of horses' natural social life which therefore should be enhanced (e.g. ensuring roughage availability, favouring group stability,, introducing socially experienced adults in groups of young horses;…). The state of the art indicates that many questions still need to be answered. Given the importance of the associated welfare issues and the consequences on the use of horses, further research is required, which could benefit horses… and humans.