Sensory laterality in affiliative interactions in domestic horses and ponies (Equus caballus)

Mainly Visual Aspects of Emotional Laterality in Cognitively Developed and Highly Social Mammals-A Systematic Review

Several studies have shown that emotions are asymmetrically represented in the human brain and have proposed three main models (the 'right hemisphere hypothesis', the 'approach-withdrawal hypothesis' and the 'valence hypothesis') that give different accounts of this emotional laterality. Furthermore, in recent years, many investigations have suggested that a similar emotional laterality may also exist in different animal taxa. However, results of a previous systematic review of emotional laterality in non-human primates have shown that some of these studies might be criticized from the methodological point of view and support only in part the hypothesis of a continuum in emotional laterality across vertebrates. The aim of the present review therefore consisted in trying to expand this survey to other cognitively developed and highly social mammals, focusing attention on mainly visual aspects of emotional laterality, in studies conducted on the animal categories of horses, elephants, dolphins and whales. The 35 studies included in the review took into account three aspects of mainly visual emotional laterality, namely: (a) visual asymmetries for positive/familiar vs. negative/novel stimuli; (b) lateral position preference in mother-offspring or other affiliative interactions; (c) lateral position preference in antagonistic interactions. In agreement with data obtained from human studies that have evaluated comprehension or expression of emotions at the facial or vocal level, these results suggest that a general but graded right-hemisphere prevalence in the processing of emotions can be found at the visual level in cognitively developed non-primate social mammals. Some methodological problems and some implications of these results for human psychopathology are briefly discussed.

Pilot study of locomotor asymmetry in horses walking in circles with and without a rider

Background

Horses commonly show asymmetries that manifest as left (L)-right (R) differences in vertical excursion of axial body segments. Moving on a circle confounds inherent individual asymmetries. Our goals were to evaluate individual and group asymmetry patterns and compare objective data with subjective impressions of side preference/laterality in horses walking on L and R circles.

Methods

Fifteen horses walked on L and R circles unridden and ridden on long and short reins. Optical motion capture (150 Hz) tracked skin-fixed markers. Variables were trunk horizontal angle; neck-to-trunk angle; vertical range of motion (ROM) for the head, withers and sacrum; ROM for pelvic roll, pitch, and yaw; mean pelvic pitch; and ROM for hip, stifle and tarsal joints. Differences between inside and outside hind steps were determined for vertical minima and maxima of the head (HMinDiff/HMaxDiff), withers (WMinDiff/WMaxDiff) and sacrum (PMinDiff/PMaxDiff). Subjective laterality was provided by owners. Data analysis used mixed models, first without and then with subjective laterality. Iterative k-means cluster analysis was used to associate biomechanical variables with subjective laterality.

Results

PMaxDiff, PMinDiff and WMaxDiff indicated R limb asymmetry in both directions. WMinDiff indicated L (inside) fore asymmetry for L direction but was close to zero for R direction. Hip ROM was significantly smaller for the inside limb in both directions (L inside/outside: 16.7° vs. 20.6°; R: 17.8° vs. 19.4°). Stifle ROM was significantly larger for the inside limb in both directions (L: 43.1° vs. 39.0°; R: 41.9° vs. 40.4°). Taking the general direction effect into account the R hip and L stifle had larger ROM. Adding laterality to the models (seven horses L- vs. six horses R-hollow), PMaxDiff R hind asymmetry was more obvious for L-hollow horses than for R-hollow horses. L-hollow horses had greater pelvic roll ROM moving in L vs. R direction. L-hollow horses had smaller inside and greater outside hip joint ROM in L vs. R direction. R-hollow horses had a significant difference in HMinDiff between L (0 mm) and R (-14 mm) directions, indicating less head lowering at outside forelimb midstance in R direction, and larger outside tarsal ROM in R (38.6°) vs. L (37.4°) direction (p ≤ 0.05). The variables that agreed most frequently with subjective laterality in cluster analysis were pelvic roll ROM, followed by HMinDiff and PMaxDiff.

Conclusion

Differences between horses walking in L and R directions were found both at group and individual levels, as well as evidence of associations with subjective laterality. Horses maintained more symmetric hip and stifle ROM and withers vertical motion when walking on the R circle. Findings suggest that left and right lateralised horses may not be perfect mirror images. Pelvic roll ROM emerged as a promising variable to determine laterality in walk as perceived by the rider, especially when considered together with other variables.

Knowledge of lateralized brain function can contribute to animal welfare

The specialized functions of each hemisphere of the vertebrate brain are summarized together with the current evidence of lateralized behavior in farm and companion animals, as shown by the eye or ear used to attend and respond to stimuli. Forelimb preference is another manifestation of hemispheric lateralization, as shown by differences in behavior between left- and right-handed primates, left- and right-pawed dogs and cats, and left- and right-limb-preferring horses. Left-limb preference reflects right hemisphere use and is associated with negative cognitive bias. Positive cognitive bias is associated with right-limb and left-hemisphere preferences. The strength of lateralization is also associated with behavior. Animals with weak lateralization of the brain are unable to attend to more than one task at a time, and they are more easily stressed than animals with strong lateralization. This difference is also found in domesticated species with strong vs. weak limb preferences. Individuals with left-limb or ambilateral preference have a bias to express functions of the right hemisphere, heightened fear and aggression, and greater susceptibility to stress. Recognition of lateralized behavior can lead to improved welfare by detecting those animals most likely to suffer fear and distress and by indicating housing conditions and handling procedures that cause stress.

Show me your best side: Lateralization of social and resting behaviors in feral horses

Growing evidence shows a variety of sensorial and motor asymmetries in social and non-social interactions in various species, indicating a lateralized processing of information by the brain. Using digital video cameras on tripods and drones, this study investigated lateralization in frequency and duration of social behavior patterns, in affiliative, agonistic, and resting contexts, in a feral population of horses (Equus ferus caballus) in Northern Portugal, consisting of 37 individuals organized in eight harem groups. Affiliative interactions (including grooming) were more often performed, and lasted longer, when recipients were positioned to the right side. In recumbent resting (animals lying down) episodes on the left side lasted longer. Our results of an affiliative behavior having a right side tendency, provide partial support to the valence-specific hypothesis of Ahern and Schwartz (1979) - left hemisphere dominance for positive affect, affiliative behaviors. Longer recumbent resting episodes on the left side may be due to synchronization. However, in both instances it is discussed how lateralization may be context dependent. Investigating the position asymmetries of social behaviors in feral equids will contribute to a better understanding of differential lateralization and hemispheric specialization from the ecological and evolutionary perspectives.

Horses discriminate human body odors between fear and joy contexts in a habituation-discrimination protocol

Animals are widely believed to sense human emotions through smell. Chemoreception is the most primitive and ubiquitous sense, and brain regions responsible for processing smells are among the oldest structures in mammalian evolution. Thus, chemosignals might be involved in interspecies communication. The communication of emotions is essential for social interactions, but very few studies have clearly shown that animals can sense human emotions through smell. We used a habituation-discrimination protocol to test whether horses can discriminate between human odors produced while feeling fear vs. joy. Horses were presented with sweat odors of humans who reported feeling fear or joy while watching a horror movie or a comedy, respectively. A first odor was presented twice in successive trials (habituation), and then, the same odor and a novel odor were presented simultaneously (discrimination). The two odors were from the same human in the fear or joy condition; the experimenter and the observer were blinded to the condition. Horses sniffed the novel odor longer than the repeated odor, indicating they discriminated between human odors produced in fear and joy contexts. Moreover, differences in habituation speed and asymmetric nostril use according to odor suggest differences in the emotional processing of the two odors.

Tend and Befriend in Horses: Partner Preferences, Lateralization, and Contextualization of Allogrooming in Two Socially Stable Herds of Quarter Horse Mares

Studies show that horses express favoritism through shared proximity and time and demonstrate unique affiliative behaviors such as allogrooming (mutual scratching) with favorite conspecifics. Allogrooming also occurs more frequently during stress and has been observed to occur more frequently in domestic herds than feral. The role of partner preference, lateralization, and duration of allogrooming as measures of social bonding has remained unclear. The present study looked at two socially stable herds of mares (n = 85, n = 115) to determine the frequency, duration, visual field of view and partner preference during allogrooming in both pasture settings (low stress) and confined settings (higher stress). One hundred and fifty-three videos for both herds were coded for allogrooming behaviors with 6.86 h recorded in confined conditions and 31.9 h in pasture settings. Six allogrooming sessions were observed in the pasture setting with an average duration of 163.11 s. In confined settings, a total of 118 allogrooming sessions were observed with an average duration of 40.98 s. Significant (p < 0.01) differences were found between settings for duration (s), number of allogrooming pairs, and frequency of allogrooming (per min) for each herd. All observed allogrooming sessions involved pairs of favored conspecifics (one partner per horse). The current study suggests that horses may have friendships that can be observed through the demonstration of specific affiliative behaviors during times of stress with more frequent, but shorter affiliative interactions with preferred partners during times of stress. This context suggests that horses adhere to the “tend and befriend” principles of friendship in animals.

Garrano Horses Perceive Letters of the Alphabet on a Touchscreen System: A Pilot Study

This study aimed to use a computer-controlled touchscreen system to examine visual discrimination in Garrano horses (Equus caballus), an endangered breed of pony belonging to the Iberian horse family. This pilot study focused on the perceptual similarity among letters of the alphabet. We tested five horses in a one-male unit (OMU) living permanently in a semi-free enclosure near their natural habitat in Serra d'Arga, northern Portugal. Horses were trained to nose-touch black circles that appeared on the screen. Then, they were tested for discrimination of five letters of the Latin alphabet in Arial font, namely O, B, V, Z, and X, using a two-choice discrimination task. The confusion matrix of letter pairs was used to show the MDS and to identify the relative contribution of shape features. The results showed perceptual similarities among letters with curvatures pitted against those of straight lines. Shape perception in horses seems to share features with that of humans and other animals living in different niches. The touchscreen system proved to be an objective and innovative way of studying cognition in the socially organized group of horses. The automated system can promote the welfare of captive horses by maximizing their freedom of movement.

Can Ponies (Equus Caballus) Distinguish Human Facial Expressions?

Communication within a species is essential for access to resources, alerting to dangers, group facilitation and social bonding; human facial expressions are considered to be an important factor in one’s ability to communicate with others. Evidence has shown that dogs and horses are able to distinguish positive and negative facial expressions by observing photographs of humans, however there is currently no research on how facial expressions from a live human are perceived by horses. This study investigated how ponies distinguish facial expressions presented by live actors. Trained actors (n = 2), using the human Facial Action Coding System, displayed four facial expressions (anger, sadness, joy and neutral) individually to twenty ponies. Heart rate and behaviors of the ponies including first monocular eye look, eye look duration (right and left side bias) and latency to approach were observed. A generalized linear mixed model (GLIMMIX) using Sidak’s multiple comparisons of least squared means determined that when exposed to anger expressions ponies looked more often with their left eye first and when exposed to joy, looked more often with their right eye first (p = 0.011). The ponies spent more time looking at angry expressions (p = 0.0003) in comparison to other expressions. There was no variation in heart rate across expressions (p > 0.89). Regardless of human facial expression, ponies looked longer (p = 0.0035), took longer to approach (p = 0.0297) and displayed more oral behaviours (p < 0.0001) with one actor than the other indicating increased arousal or negative valence. Ponies with more experience as a lesson mount had lower heart rates (p < 0.0001) carried their head lower (p < 0.0001), kept their left ear on the actor (p < 0.03) and exhibited more oral behaviours (p < 0.0001) than ponies with less experience. This study demonstrates that ponies are able to distinguish facial expressions presented by a live human, but other factors also contribute to their responses to humans.

Laterality in Horse Training: Psychological and Physical Balance and Coordination and Strength Rather Than Straightness

Simple Summary

For centuries, straightening a horse has been considered a key element in achieving its responsiveness and suppleness and has been a traditional goal in training. However, body asymmetry (natural crookedness), motor laterality (the preference for limbs on one side) and sensory laterality (the preference for sensory organs on one side) are naturally occurring phenomena. In humans, the forced correction of these imbalances, for example, forcing left-handed children to write with their right hands, has been shown to lead to psychological imbalance. In view of this, lateral asymmetries in horses should be accepted, and training should focus on psychological and physical balance, coordination and equal strength on both sides, instead of enforcing “straightness”. To explore this, we conducted a review of the literature on motor and sensory laterality in horses and found that the evidence suggests that enforcing straightness may be stressful and may even be counterproductive by causing psychological and physical imbalance relative to a horse, making it tense and uncooperative. In general, body asymmetry has been shown to have little impact on performance, but increases in motor and sensory laterality can indicate insufficiencies in housing, handling and training. We, therefore, propose that laterality should be recognized as a welfare indicator and that straightness in a horse should be achieved by conducting training focused on balance, coordination and equal strength on both sides.

Abstract

For centuries, a goal of training in many equestrian disciplines has been to straighten the horse, which is considered a key element in achieving its responsiveness and suppleness. However, laterality is a naturally occurring phenomenon in horses and encompasses body asymmetry, motor laterality and sensory laterality. Furthermore, forcibly counterbalancing motor laterality has been considered a cause of psychological imbalance in humans. Perhaps asymmetry and laterality should rather be accepted, with a focus on training psychological and physical balance, coordination and equal strength on both sides instead of enforcing “straightness”. To explore this, we conducted a review of the literature on the function and causes of motor and sensory laterality in horses, especially in horses when trained on the ground or under a rider. The literature reveals that body asymmetry is innate but does not prevent the horse from performing at a high level under a rider. Motor laterality is equally distributed in feral horses, while in domestic horses, age, breed, training and carrying a rider may cause left leg preferences. Most horses initially observe novel persons and potentially threatening objects or situations with their left sensory organs. Pronounced preferences for the use of left sensory organs or limbs indicate that the horse is experiencing increased emotionality or stress, and long-term insufficiencies in welfare, housing or training may result in left shifts in motor and sensory laterality and pessimistic mentalities. Therefore, increasing laterality can be regarded as an indicator for insufficiencies in housing, handling and training. We propose that laterality be recognized as a welfare indicator and that straightening the horse should be achieved by conducting training focused on balance, coordination and equal strength on both sides.

Does Carrying a Rider Change Motor and Sensory Laterality in Horses?

Simple Summary

Laterality, or one-sidedness, has been studied in many species, including horses, and has been linked to factors such as stress and emotionality. Today, although most horses are used for riding, the impact that carrying a rider has on their sensory (preferred side of sensory organs) and motor (preferred side of body usage) laterality has not been researched to date. In this study, 23 horses were tested to assess, firstly, motor laterality by observing which foreleg a horse would use to step over a pole and, secondly, sensory laterality by observing the preferred side of sensory organs when exposed to (a) an unknown person and (b) a novel object. All three experiments were conducted with and without a rider. The rider gave minimal aids and rode on a long rein to allow the horse free choice. The results of this preliminary study show that the strength of motor laterality (the number of times the preferred foreleg was used) increased when horses carried a rider but that sensory laterality did not change. This suggests that carrying a rider who is as passive as possible does not have an adverse effect on a horse’s stress levels and mental state.

Abstract

Laterality in horses has been studied in recent decades. Although most horses are kept for riding purposes, there has been almost no research on how laterality may be affected by carrying a rider. In this study, 23 horses were tested for lateral preferences, both with and without a rider, in three different experiments. The rider gave minimal aids and rode on a long rein to allow the horse free choice. Firstly, motor laterality was assessed by observing forelimb preference when stepping over a pole. Secondly, sensory laterality was assessed by observing perceptual side preferences when the horse was confronted with (a) an unfamiliar person or (b) a novel object. After applying a generalised linear model, this preliminary study found that a rider increased the strength of motor laterality (p = 0.01) but did not affect sensory laterality (p = 0.8). This suggests that carrying a rider who is as passive as possible does not have an adverse effect on a horse’s stress levels and mental state.

Horses show individual level lateralisation when inspecting an unfamiliar and unexpected stimulus

Animals must attend to a diverse array of stimuli in their environments. The emotional valence and salience of a stimulus can affect how this information is processed in the brain. Many species preferentially attend to negatively valent stimuli using the sensory organs on the left side of their body and hence the right hemisphere of their brain. Here, we investigated the lateralisation of visual attention to the rapid appearance of a stimulus (an inflated balloon) designed to induce an avoidance reaction and a negatively valent emotional state in 77 Italian saddle horses. Horses’ eyes are laterally positioned on the head, and each eye projects primarily to the contralateral hemisphere, allowing eye use to be a proxy for preferential processing in one hemisphere of the brain. We predicted that horses would inspect the novel and unexpected stimulus with their left eye and hence right hemisphere. We found that horses primarily inspected the balloon with one eye, and most horses had a preferred eye to do so, however, we did not find a population level tendency for this to be the left or the right eye. The strength of this preference tended to decrease over time, with the horses using their non-preferred eye to inspect the balloon increasingly as the trial progressed. Our results confirm a lateralised eye use tendency when viewing negatively emotionally valent stimuli in horses, in agreement with previous findings. However, there was not any alignment of lateralisation at the group level in our sample, suggesting that the expression of lateralisation in horses depends on the sample population and testing context.

Visual lateralization in artiodactyls: A brief summary of research and new evidence on saiga antelope

The visual system and lifestyle characteristics make the even-toed ungulates an excellent model for the studies of behavioural lateralization. Recent research has focused on these mammals providing evidence of lateralization in a wide range of behaviours. This provides an opportunity for the collation of the current theoretical assumptions and the existing empirical evidence for visual lateralization in artiodactyls. In the present study, we aim first to gain a fuller picture of hemispheric specializations in saiga antelopes by investigating the lateralization of vigilance and novel object inspection in the wild. Second, we summarized the results of the research into visual lateralization in even-toed ungulates and attempted to assess the applicability of two popular hypotheses about the division of hemispheric roles. The results on saigas show a significant preference for head turns to the right visual field during vigilance which was more robust in individuals in larger groups. When an unfamiliar artificial object was placed in their natural setting, saigas preferentially viewed it predominantly with the right eye. These results, together with the cumulative evidence in artiodactyls, do not follow either the approach-withdrawal or positivity-negativity dichotomous patterns widely used to explain the division of functions between the hemispheres.

A Systematic Approach to Dissection of the Equine Brain-Evaluation of a Species-Adapted Protocol for Beginners and Experts

Introduction of new imaging modalities for the equine brain have refocused attention on the horse as a natural model for ethological, neuroanatomical, and neuroscientific investigations. As opposed to imaging studies, strategies for equine neurodissection still lack a structured approach, standardization and reproducibility. In contrast to other species, where adapted protocols for sampling have been published, no comparable guideline is currently available for equids. Hence, we developed a species-specific slice protocol for whole brain vs. hemispheric dissection and tested its applicability and practicability in the field, as well as its neuroanatomical accuracy and reproducibility. Dissection steps are concisely described and depicted by schematic illustrations, photographs and instructional videos. Care was taken to show the brain in relation to the raters' hands, cutting devices and bench surface. Guidance is based on a minimum of external anatomical landmarks followed by geometric instructions that led to procurement of 14 targeted slabs. The protocol was performed on 55 formalin-fixed brains by three groups of investigators with different neuroanatomical skills. Validation of brain dissection outcomes addressed the aptitude of slabs for neuroanatomical studies as opposed to simplified routine diagnostic purposes. Across all raters, as much as 95.2% of slabs were appropriate for neuroanatomical studies, and 100% of slabs qualified for a routine diagnostic setting. Neither autolysis nor subfixation significantly affected neuroanatomical accuracy score, while a significant negative effect was observed with brain extraction artifacts. Procedure times ranged from 14 to 66 min and reached a mean duration of 23.25 ± 7.93 min in the last of five trials in inexperienced raters vs. 16 ± 2.83 min in experts, while acceleration of the dissection did not negatively impact neuroanatomical accuracy. This protocol, derived analogously to the consensus report of the International Veterinary Epilepsy Task Force in dogs and cats, allows for systematic, quick and easy dissection of the equine brain, even for inexperienced investigators. Obtained slabs feature virtually all functional subcompartments at suitable planes for both diagnostic and neuroscientific investigations and complement the data obtained from imaging studies. The instructive protocol and brain dissection videos are available in Supplementary Material.

Sensory Abilities of Horses and Their Importance for Equitation Science

Vision, hearing, olfaction, taste, and touch comprise the sensory modalities of most vertebrates. With these senses, the animal receives information about its environment. How this information is organized, interpreted, and experienced is known as perception. The study of the sensory abilities of animals and their implications for behavior is central not only to ethology but also to animal welfare. Sensory ability, perception, and behavior are closely linked. Horses and humans share the five most common sensory modalities, however, their ranges and capacities differ, so that horses are unlikely to perceive their surroundings in a similar manner to humans. Understanding equine perceptual abilities and their differences is important when horses and human interact, as these abilities are pivotal for the response of the horse to any changes in its surroundings. This review aims to provide an overview of the current knowledge on the sensory abilities of horses. The information is discussed within an evolutionary context and also includes a practical perspective, outlining potential ways to mitigate risks of injuries and enhance positive horse-human interactions. The equine sensory apparatus includes panoramic visual capacities with acuities similar to those of red-green color-blind humans as well as aural abilities that, in some respects exceed human hearing and a highly developed sense of smell, all of which influence how horses react in various situations. Equine sensitivity to touch has been studied surprisingly sparingly despite tactile stimulation being the major interface of horse training. We discuss the potential use of sensory enrichment/positive sensory stimulation to improve the welfare of horses in various situations e.g. using odors, touch or sound to enrich the environment or to appease horses. In addition, equine perception is affected by factors such as breed, individuality, age, and in some cases even color, emphasizing that different horses may need different types of management. Understanding the sensory abilities of horses is central to the emerging discipline of equitation science, which comprises the gamut of horse-human interactions. Therefore, sensory abilities continue to warrant scientific focus, with more research to enable us to understand different horses and their various needs.

Female horses spontaneously identify a photograph of their keeper, last seen six months previously

Horses are capable of identifying individual conspecifics based on olfactory, auditory or visual cues. However, this raises the questions of their ability to recognize human beings and on the basis of what cues. This study investigated whether horses could differentiate between a familiar and unfamiliar human from photographs of faces. Eleven horses were trained on a discrimination task using a computer-controlled screen, on which two photographs were presented simultaneously (32 trials/session): touching one was rewarded (S+) and the other not (S−). In the training phase, the S+ faces were of four unfamiliar people which gradually became familiar over the trials. The S− faces were novel for each trial. After the training phase, the faces of the horses’ keepers were presented opposite novel faces to test whether the horses could identify the former spontaneously. A reward was given whichever face was touched to avoid any possible learning effect. Horses touched the faces of keepers significantly more than chance, whether it was their current keeper or one they had not seen for six months (t = 3.65; p < 0.004 and t = 6.24; p < 0.0001). Overall, these results show that horses have advanced human face-recognition abilities and a long-term memory of those human faces.

Equestrian and biomechanical perspectives on laterality in the horse

It has been suggested that one of the underlying causes of asymmetrical performance and left/right bias in sound riding horses is laterality originating in the cerebral cortices described in many species. The aim of this paper is to review the published evidence for inherent biomechanical laterality in horses deemed to be clinically sound and relate these findings to descriptions of sidedness in equestrian texts. There are no established criteria to determine if a horse is left or right dominant but the preferred limb has been defined as the forelimb that is more frequently protracted during stance and when grazing. Findings on left-right differences in forelimb hoof shape and front hoof angles have been linked to asymmetric forelimb ground reaction forces. Asymmetries interpreted as motor laterality have been found among foals and unhandled youngsters, and the consistency or extent of asymmetries seems to increase with age. Expressions of laterality also vary with breed, sex, training and handling, stress, and body shape but there are no studies of the possible link between laterality and lameness. In a recent study of a group of seven dressage horses, a movement pattern in many ways similar to descriptions of sidedness in the equestrian literature, e.g. one hind limb being more protracted and placed more laterally than the other, has been documented. The role of innate laterality versus painful conditions, training, human handedness and simply habit remains to be determined. Understanding the biomechanical manifestations of laterality in healthy horses, including individual variation, would yield a potential basis for how laterality should be taken into account in relation to training/riding and rehabilitation of lameness.

Non-invasive stress evaluation in domestic horses (Equus caballus): impact of housing conditions on sensory laterality and immunoglobulin A

The study aimed to evaluate sensory laterality and concentration of faecal immunoglobulin A (IgA) as non-invasive measures of stress in horses by comparing them with the already established measures of motor laterality and faecal glucocorticoid metabolites (FGMs). Eleven three-year-old horses were exposed to known stressful situations (change of housing, initial training) to assess the two new parameters. Sensory laterality initially shifted significantly to the left and faecal FGMs were significantly increased on the change from group to individual housing and remained high through initial training. Motor laterality shifted significantly to the left after one week of individual stabling. Faecal IgA remained unchanged throughout the experiment. We therefore suggest that sensory laterality may be helpful in assessing acute stress in horses, especially on an individual level, as it proved to be an objective behavioural parameter that is easy to observe. Comparably, motor laterality may be helpful in assessing long-lasting stress. The results indicate that stress changes sensory laterality in horses, but further research is needed on a larger sample to evaluate elevated chronic stress, as it was not clear whether the horses of the present study experienced compromised welfare, which it has been proposed may affect faecal IgA.

Equine Stereotaxtic Population Average Brain Atlas With Neuroanatomic Correlation

There is growing interest in the horse for behavioral, neuroanatomic and neuroscientific research due to its large and complex brain, cognitive abilities and long lifespan making it neurologically interesting and a potential large animal model for several neuropsychological diseases. Magnetic resonance imaging (MRI) is a powerful neuroscientific research tool that can be performed in vivo, with adapted equine facilities, or ex-vivo in the research setting. The brain atlas is a fundamental resource for neuroimaging research, and have been created for a multitude animal models, however, none currently exist for the equine brain. In this study, we document the creation of a high-resolution stereotaxic population average brain atlas of the equine. The atlas was generated from nine unfixed equine cadaver brains imaged within 4 h of euthanasia in a 3-tesla MRI. The atlas was generated using linear and non-linear registration methods and quality assessed using signal and contrast to noise calculations. Tissue segmentation maps (TSMs) for white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF), were generated and manually segmented anatomic priors created for multiple subcortical brain structures. The resulting atlas was validated and correlated to gross anatomical specimens and is made freely available at as an online resource for researchers (https://doi.org/10.7298/cyrs-7b51.2). The mean volume metrics for the whole brain, GM and WM for the included subjects were documented and the effect of age and laterality assessed. Alterations in brain volume in relation to age were identified, though these variables were not found to be significantly correlated. All subjects had higher whole brain, GM and WM volumes on the right side, consistent with the well documented right forebrain dominance of horses. This atlas provides an important tool for automated processing in equine and translational neuroimaging research.

From Science to Practice: A Review of Laterality Research on Ungulate Livestock

In functional laterality research, most ungulate livestock species have until recently been mainly overlooked. However, there are many scientific and practical benefits of studying laterality in ungulate livestock. As social, precocial and domestic species, they may offer insight into the mechanisms involved in the ontogeny and phylogeny of functional laterality and help to better understand the role of laterality in animal welfare. Until now, most studies on ungulate livestock have focused on motor laterality, but interest in other lateralized functions, e.g., cognition and emotions, is growing. Increasingly more studies are also focused on associations with age, sex, personality, health, stress, production and performance. Although the full potential of research on laterality in ungulate livestock is not yet exploited, findings have already shed new light on central issues in cognitive and emotional processing and laid the basis for potentially useful applications in future practice, e.g., stress reduction during human-animal interactions and improved assessments of health, production and welfare. Future research would benefit from further integration of basic laterality methodology (e.g., testing for individual preferences) and applied ethological approaches (e.g., established emotionality tests), which would not only improve our understanding of functional laterality but also benefit the assessment of animal welfare.

Differential roles of the right and left brain hemispheres in the social interactions of a free-ranging ungulate

Despite the abundant empirical evidence on lateralized social behaviours, a clear understanding of the relative roles of two brain hemispheres in social processing is still lacking. This study investigated visual lateralization in social interactions of free-ranging European bison (Bison bonasus). The bison were more likely to display aggressive responses (such as fight and side hit), when they viewed the conspecific with the right visual field, implicating the left brain hemisphere. In contrast, the responses associated with positive social interactions (female-to-calf bonding, calf-to-female approach, suckling) or aggression inhibition (fight termination) occurred more likely when the left visual field was in use, indicating the right hemisphere advantage. The results do not support either assumptions of right-hemisphere dominance for control of various social functions or hypotheses about simple positive (approach) versus negative (withdrawal) distinction between the hemispheric roles. The discrepancy between the studies suggests that in animals, the relative roles of the hemispheres in social processing may be determined by a fine balance of emotions and motivations associated with the particular social reaction difficult to categorize for a human investigator. Our findings highlight the involvement of both brain hemispheres in the control of social behaviour.

Horses' (Equus Caballus) Laterality, Stress Hormones, and Task Related Behavior in Innovative Problem-Solving

Domesticated horses are constantly confronted with novel tasks. A recent study on anecdotal data indicates that some are innovative in dealing with such tasks. However, innovative behavior in horses has not previously been investigated under experimental conditions. In this study, we investigated whether 16 horses found an innovative solution when confronted with a novel feeder. Moreover, we investigated whether innovative behavior in horses may be affected by individual aspects such as: age, sex, size, motor and sensory laterality, fecal stress hormone concentrations (GCMs), and task-related behavior. Our study revealed evidence for 25% of the horses being capable of innovative problem solving for operating a novel feeder. Innovative horses of the present study were active, tenacious, and may be considered to have a higher inhibitory control, which was revealed by their task related behavior. Furthermore, they appeared to be emotional, reflected by high baseline GCM concentrations and a left sensory and motor laterality. These findings may contribute to the understanding of horses' cognitive capacities to deal with their environment and calls for enriched environments in sports and leisure horse management.

What do wild saiga antelopes tell us about the relative roles of the two brain hemispheres in social interactions?

Two brain hemispheres are unequally involved in the processing of social stimuli, as demonstrated in a wide range of vertebrates. A considerable number of studies have shown the right hemisphere advantage for social processing. At the same time, an approach-withdrawal hypothesis, mainly based on experimental evidence, proposes the involvement of both brain hemispheres according to approach and withdrawal motivation. The present study aimed to test the relative roles of the two hemispheres in social responses displayed in a natural context. Visual biases, implicating hemispheric lateralization, were estimated in the social interactions of saiga antelope in the wild. In individually identified males, the left/right visual field use during approach and withdrawal responses was recorded based on the lateral head/body position, relative to the conspecific. Lateralized approach responses were investigated in three types of interactions, with left visual field bias found for chasing a rival, no bias-for attacking a rival, and right visual field bias-for pursuing a female. In two types of withdrawal responses, left visual field bias was found for retreating after fighting, while no bias was evident in fight rejecting. These findings demonstrate that neither the right hemisphere advantage nor the approach-withdrawal distinction can fully explain the patterns of lateralization observed in social behaviour. It is clear that both brain hemispheres play significant roles in social responses, while their relative contribution is likely determined by a complex set of motivational and emotional factors rather than a simple dichotomous distinction such as, for example, approach versus withdrawal motivation.

Evidence for Right-Sided Horses Being More Optimistic than Left-Sided Horses

An individual's positive or negative perspective when judging an ambiguous stimulus (cognitive bias) can be helpful when assessing animal welfare. Emotionality, as expressed in approach or withdrawal behaviour, is linked to brain asymmetry. The predisposition to process information in the left or right brain hemisphere is displayed in motor laterality. The quality of the information being processed is indicated by the sensory laterality. Consequently, it would be quicker and more repeatable to use motor or sensory laterality to evaluate cognitive bias than to perform the conventional judgment bias test. Therefore, the relationship between cognitive bias and motor or sensory laterality was tested. The horses (n = 17) were trained in a discrimination task involving a box that was placed in either a "positive" or "negative" location. To test for cognitive bias, the box was then placed in the middle, between the trained positive and negative location, in an ambiguous location, and the latency to approach the box was evaluated. Results indicated that horses that were more likely to use the right forelimb when moving off from a standing position were more likely to approach the ambiguous box with a shorter latency (generalized linear mixed model, p < 0.01), and therefore displayed a positive cognitive bias (optimistic).