Jun 142010
 

Here are a collection of abstracts from the lastest scientific papers, published in the first half of this year. Whether you are a casual rider or a professional horse person this is information that you need to know. I hope you enjoy this collection of abstracts as much as I did. If you have a question about any of the below abstracts, or the terminology used, please feel free to leave a comment and I will happily answer your questions.

Behaviour

Discrimination between conspecific odour samples in the horse (Equus caballus)

Becky Hothersall, Patricia Harris, Lotta Sörtoft and Christine J. Nicol

Abstract- Behavioural observations suggest that smell is important in social discriminations between horses but balanced studies of this capacity are lacking. We used a habituation–discrimination procedure to investigate the ability of horses to distinguish between pairs of odour samples from different individuals. In Study 1, separate tests were conducted for urine, faeces or fleece fabric previously rubbed on the coat (to pick up body odour samples (BOS)) and donor pairs differed in sex, and age. 10 pregnant mares each underwent three tests, one per sample type. A test consisted of three successive 2-min presentations of a sample from Individual A with a simultaneous presentation of a sample from Individual B during the final presentation. Doubly repeated measures ANOVA indicated a main effect of sample type on investigative response (df = 2, f = 7.98, P = 0.004): durations were longer for BOS than for urine or faeces but habituation across trials was most consistent for urine. In the final presentation, mares demonstrated discrimination by investigating the novel urine sample (B) more than the repeated sample (novel: median 8.0s, IQR = 10; repeated: median 2.5s, IQR = 6; z = −2.558, P = 0.008). In Study 2, urine samples from castrated male donors were used and neither mares nor their 4-month-old foals discriminated between samples from different individuals in the final presentation. The findings suggest that urine odour may contain some information that horses can use to discriminate between conspecifics. This may be limited to the level of broad categories such as sex or reproductive status; further investigation is needed to reveal what functional information can be transmitted and what compounds are involved.

Link – http://www.sciencedirect.com/science

Fear reactions in trained and untrained horses from dressage and show-jumping breeding lines

U. Von Borstel, I.J.H. Duncan, M.C. Lundin and L.J. Keeling.

Abstract- Horses’ fear reactions are hazardous to both horses and human beings, but it is not clear whether fear is influenced more by training or by other factors such as genetics. The following study was designed to detect differences between young, untrained (U) and older, well-trained (T) horses of dressage (D), show-jumping (J), and mixed (M) genetic lines with regard to intensity of reaction and ease of habituation to a frightening stimulus. In five consecutive trials, 90 horses were exposed to a standardized fear-eliciting stimulus where intensity and duration of the reactions were recorded. Repeated measures analysis showed that flight reactions by J were less intense (p >0.05) than those by D or M regardless of training status or age. Habituation to the stimulus over time was not significantly (p >0.1) different between the disciplines, as indicated by similar slopes for all measurements, but reaction vigour declined faster for T than for U. These findings indicate that there may be a genetic basis for less strong, though not shorter-lasting, fear reactions in J compared to D or M lines of horses. Research including the estimation of genetic correlations between traits related to fearfulness and to performance would be required to verify this assumption.

Link – http://www.appliedanimalbehaviour.com/article/S0168-1591(10)00136-X/abstract

Monitoring distances travelled by horses using GPS tracking collars

BA Hampson, JM Morton, PC Mills, MG Trotter, DW Lamb and CC Pollitt

Abstract – Objective The aims of this work were to (1) develop a low-cost equine movement tracking collar based on readily available components, (2) conduct preliminary studies assessing the effects of both paddock size and internal fence design on the movements of domestic horses, with and without foals at foot, and (3) describe distances moved by mares and their foals. Additional monitoring of free-ranging feral horses was conducted to allow preliminary comparisons with the movement of confined domestic horses. Procedures A lightweight global positioning system (GPS) data logger modified from a personal/vehicle tracker and mounted on a collar was used to monitor the movement of domestic horses in a range of paddock sizes and internal fence designs for 6.5-day periods. Results In the paddocks used (0.8–16 ha), groups of domestic horses exhibited a logarithmic response in mean daily distance travelled as a function of increasing paddock size, tending asymptotically towards approximately 7.5 km/day. The distance moved by newborn foals was similar to their dams, with total distance travelled also dependent on paddock size. Without altering available paddock area, paddock design, with the exception of a spiral design, did not significantly affect mean daily distance travelled. Feral horses (17.9 km/day) travelled substantially greater mean daily distances than domestic horses (7.2 km/day in 16-ha paddock), even when allowing for larger paddock size. Conclusions. Horses kept in stables or small yards and paddocks are quite sedentary in comparison with their feral relatives. For a given paddock area, most designs did not significantly affect mean daily distance travelled.

Link – http://www3.interscience.wiley.com/journal/123356045/abstract

Equine Development

The effect of early handling of foals on their reaction to handling, humans and novelty, and the foal–mare relationship

E. Sondergaard and J. Jago

Abstract – The natural behaviour of horses in response to danger is to take flight, and consequently human handlers can be injured. Reducing the flight response and general reactivity of horses is therefore likely to reduce the incidence of injuries to handlers. In this experiment we investigated the effect of handling foals in the first 2 days after birth on their subsequent response to handling, humans and novelty, and the foal–mare relationship. Standardbred foals were assigned to one of two groups, handled (H) (N = 22, 12 colts, 10 fillies) and control (C) (N = 22, 11 colts, 11 fillies). Handling took place 3 times/day on days 1 and 2 after birth for 10 >min/session. Individual foals were gently restrained and stroked all over their body using bare hands and then a plastic bag and each leg was lifted once. C foals received no handling. C and H foals did not differ in their reaction to freeze branding at a mean age of 14 days. The approach and leave behaviour of mare–foal pairs were observed at pasture during week 5 to evaluate their relationship. Mares of H foals were less active in keeping the pair together than mares of C foals (GLM: 6.81; P < 0.05). At 6 weeks of age all colts were introduced to an arena, together with their mare, and their reaction to a novel object and an unknown human were tested. Treatment did not affect heart rate of foals or in mares. C foals initiated more suckling bouts than H when no human was present (Wilcoxon: Z = 2.44, N = 22, P < 0.05) indicating that they responded differently to the novel arena than H foals. However, there was no difference between H and C foals in their exploratory behaviour in the arena. When a human was present in the arena, H foals had a shorter flight distance than C foals (Z= −1.98, N= 22, P < 0.05) and tended to move further away from the mare (Z= −1.80, N= 22, P< 0.07). Handling of foals in the first 2 days after birth appeared to affect the foal–mare relationship and alter their perception of humans at a later age but did not alter their response to novelty or to handling. The effects of early handling of foals on the foal–mare relationship require further investigation.

Link – http://www.appliedanimalbehaviour.com/article/S0168-1591(10)00029-8/abstract

Effects of imprint training procedure at birth on the reactions of foals at age six months

J. L. WILLIAMS, T. H. FRIEND, M. N. COLLINS, M. J. TOSCANO, A. SISTO-BURT and C.H. NEVILL

Abstract – Reasons for performing study: While imprint training procedures have been promoted in popular magazines, they have received limited scientific investigation. Objectives: To determine the effects of a neonatal imprint training procedure on 6-month-old foals and to determine if any one session had a greater effect than others. Methods: Foals (n = 131) were divided into the following treatments: no imprint training, imprint training at birth, 12, 24 and 48 h after birth or imprint training only at birth, 12, 24, 48, or 72 h after birth. Foals then received minimal human handling until they were tested at 6 months. Results: During training, time to complete exposure to the stimulus was significant for only 2 of 6 stimuli. Percentage change in baseline heart rate was significant for only 2 of 10 stimuli. These 4 effects were randomly spread across treatments. Conclusions: Neither the number of imprint training sessions (0, 1, or 4) nor the timing of imprint training sessions (none, birth, 12, 24, 48, or 72 h after birth) influenced the foal’s behaviour at 6 months of age. Potential clinical relevance: In this study, imprint training did not result in better behaved, less reactive foals.

Link -http://www3.interscience.wiley.com/journal/123228952/abstract

Horse Training

Positive interactions lead to lasting positive memories in horses, Equus caballus.

Carol Sankey, Marie-Annick Richard-Yris, Helene Leroy, Severine Henry, and Martine Hausberger.

Abstract- Social relationships are important in social species. These relationships, based on repeated interactions, define each partner’s expectations during the following encounters. The creation of a relationship implies high social cognitive abilities which require that each partner is able to associate the positive or negative content of an interaction with a specific partner and to recall this association. In this study, we tested the effects of repeated interactions on the memory kept by 23 young horses about humans, after 6 and 8 months of separation. The association of a reward with a learning task in an interactional context induced positive reactions towards humans during training. It also increased contact and interest, not only just after training, but also several months later, despite no further interaction with humans. In addition, this ‘positive memory’ of humans extended to novel persons. Overall, positive reinforcement enhanced learning and memorization of the task itself. These findings suggest remarkable social cognitive abilities that can be transposed from intraspecific to interspecific social contexts.

Link- http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W9W-4YBX1RW-1&_user=10&_coverDate=04%2F30%2F2010&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1369489598&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=47c2752e3aabb8c1c1304cbfddc73aef

The use of human-given cues by domestic horses, Equus caballus, during an object choice task

Meggen Walton and Karen McComb

Abstract – Selection pressures during domestication are thought to lead to an enhanced ability to use human-given cues. Horses fulfil a wide variety of roles for humans and have been domesticated for at least 5000 years but their ability to read human cues has not been widely studied. We tested the ability of 28 horses to attend to human-given cues in an object choice task. We included five different cues: distal sustained pointing, momentary tapping, marker placement, body orientation and gaze (head) alternation. Horses were able to use the pointing and marker placement cues spontaneously but not the tapping, body orientation and gaze alternation cues. The overall pattern of responding suggests that horses may use cues that provide stimulus enhancement at the time of choice and do not have an understanding of the communicative nature of the cues given. As such, their proficiency at this task appears to be inferior to that of domestic dogs, Canis lupus familiaris, but similar to that of domestic goats, Caprus hircus.

Link – http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W9W-4YT09DP-1&_user=10&_coverDate=06%2F30%2F2010&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1369491728&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=eb6e37f1c4cbefc1c23d49f601b6d234

Human facial discrimination in horses: can they tell us apart?

Sherril M. Stone

Abstract – The human–horse relationship has a long evolutionary history. Horses continue to play a pivotal role in the lives of humans and it is common for humans to think their horses recognize them by face. If a horse can distinguish his/her human companion from other humans, then evolution has supplied the horse with a very adaptive cognitive ability. The current study used operant conditioning trials to examine whether horses could discriminate photographed human faces and transfer this facial recognition ability a novel setting. The results indicated the horses (a) learned to discriminate photographs of the unrelated individuals, fraternal twins, and identical twins and (b) demonstrated transfer of facial recognition by spending more time with their S+ woman in the field test.

Link – http://www.springerlink.com/content/jg20884g612471h4/

Horses’ learning performances are under the influence of several temperamental dimensions

L. Lansade and F. Simon

Abstract – Learning performances are influenced by many factors, not only breed, age and sex, but also temperament. The purpose of this study was to understand how different temperamental dimensions affect the learning performance of horses, Equus caballus. First, we carried out a series of behavioural tests on 36 Welsh ponies aged 5–7 years to measure five temperamental dimensions: fearfulness (novel area test and surprise test), gregariousness (social isolation test), reactivity to humans (passive human test), tactile sensitivity (von Frey filament test) and activity level (evaluation of locomotor activity during all the tests). We then presented them with two learning tasks (avoidance and backwards–forwards tasks). In the avoidance task they had to learn to jump over a fence when they heard a sound associated with an aversive stimulus (puff of air). In the backwards–forwards task they had to walk forwards or move backwards in response to a tactile or vocal command to obtain a food reward. There was no correlation between performances on the two learning tasks, indicating that learning ability is task-dependent. However, correlations were found between temperamental data and learning performance (Spearman correlations). The ponies that performed the avoidance task best were the most fearful and the most active ones. For instance, the number of trials required to perform 5 consecutive correct responses (learning criterion) was correlated with the variables aimed at measuring fearfulness (way of crossing a novel area: rs= −0.41, P = 0.01 and time to start eating again after a surprise effect: rs = −0.33, P= 0.05) and activity level (frequency of trotting during all the tests: rs= −0.40, P= 0.02). The animals that performed the backwards–forwards task best were the ones that were the least fearful and the most sensitive. For instance, the learning criterion (corresponding to the number of trials taken to achieve five consecutive correct responses) was correlated with the variables aimed at measuring fearfulness (latency to put one foot on the area: rs= 0.43, P= 0.01; way of crossing a novel area: rs=0.31, P= 0.06; and time to start eating again after a surprise effect: rs= 0.43, P= 0.009) and tactile sensitivity (response to von Frey filaments: rs= −0.44, P = 0.008). This study revealed significant links between temperament and learning abilities that are highly task-dependent.

Link – http://www.appliedanimalbehaviour.com/article/S0168-1591(10)00074-2/abstract

Management

Effect of housing conditions on activity and lying behaviour of horses

S.J Chaplin and L. Gretgrix

Abstract – Housing conditions for horses impose various levels of confinement, which may compromise welfare. Lying behaviour and activity can be used as welfare indicators for domestic animals and rebound behaviour suggests a build-up of motivation resulting from deprivation. The objective of this study was to determine if activity and lying behaviour of horses are affected by housing conditions and to investigate the occurrence of rebound behaviour after release from confinement. Eight horses were subjected, in pairs, to each of four experimental treatments; paddock (P), fully stabled (FS), partly stabled (PS) and yard (Y). Each horse received 6 days acclimatisation prior to the 24 h recording period. Time spent in lying and activity were electronically recorded using a tilt switch and motion sensor connected to a data logger worn on the horse’s left foreleg. Time spent active during the first 5 min of release from stable to paddock in the PS treatment (days 1 and 5) and at the same time of day in the P treatment was used as a measure of rebound behaviour. Effect of housing conditions on total time spent active was highly significant (FS = 123 s, PS = 158 s, Y = 377 s, P = 779 s, P < 0.001). Housing conditions did not significantly affect total time spent lying (P = 0.646). Horses were significantly more active, compared with baseline paddock behaviour, on release from stabling on both days 1 (P = 0.006) and 5 (P = 0.025) of PS treatment. These results suggest that activity patterns of horses, but not lying behaviour, are affected by the housing conditions tested and that rebound activity occurs in horses after a period of confinement.

Link – http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7466644

Riding

Preliminary study of jointed snaffle vs. crossunder bitless bridles: Quantified comparison of behaviour in four horses

W. R. Cook and D. S. Mills,

Abstract – The study tested the null hypothesis that if a horse is ridden in a snaffle bridle and then a crossunder bitless bridle, there will be no change in its behaviour. It was predicted that there would be change and that behaviour would improve when bitless. Four horses, none of which had ever been ridden in a crossunder bitless bridle, were ridden through two 4 min, exercise tests, first bitted then bitless. An independent judge marked the 27 phases of each test on a 10 point scale and comments and scores were recorded on a video soundtrack. The results refuted the null hypothesis and upheld the predictions. Mean score, when bitted, was 37%; and through the first 4 min of being bitless, 64%. A binomial probability distribution suggested that the results were significantly different from random effects. All 4 horses accepted the crossunder bitless bridle without hesitation. Further studies are warranted and it is hoped that others will build on this new field of investigation. The authors are of the opinion that the bit can be a welfare and safety problem for both horse and horseman. Equestrian organisations that currently mandate use of the bit for competitions are urged to review their rules.

Link – http://www3.interscience.wiley.com/journal/123230824/abstract

A comparison of forces acting on the horse’s back and the stability of the rider’s seat in different positions at the trot

A.B. Kotschwar, B. Borkenhagen, S. Kuhnke, J. Molsner and A. Baltacis

Abstract -The aim of the study was to compare the stability of the rider as well as the forces acting on a horse’s back with different seating positions at the trot (sitting trot, rising trot and two-point seat). The same experienced rider was mounted on 10 sound horses trotting on a treadmill. The kinetic data were recorded with an electronic pressure mat, placed under a well-fitting dressage saddle with no saddle pad. The rider used three different seating positions, each for 20s. Right forelimb motion was used to synchronise the pressure data with the stride cycles. To determine the rider’s stability, the movement of the centre of pressure (COP) along the transverse (X) and longitudinal (Y) axes was calculated. The force was taken as the sum of all segments of the pressure pad multiplied by the area of the pressure pad. The maximum force and the X- and Y-deviations were evaluated using ANOVA for repeated measures with a Bonferroni Post hoc test. The stability of the rider in the Y-direction was significantly highest in the two-point seat, followed by the rising trot and the sitting trot, respectively. In the X-direction, there was no significant difference between the three positions. The significantly highest load on the horse’s back was at the sitting trot (2112N), followed by the rising trot (2056N) and the two-point seat (1688N). The rider was most stable in the two-point seat while transferring the lowest load on the horse’s back. The rising trot was found to be more stable and less stressful for the horse’s back compared to the sitting trot.

Link – http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WXN-4W80GHX-1&_user=10&_coverDate=04%2F30%2F2010&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1369499043&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f7f5c89c58d102c20197b1e6134e0579

Stereotypic Behaviours (Stable Vices)

Crib-biting in US horses: Breed predispositions and owner perceptions of aetiology

J. D. ALBRIGHT H. O. MOHAMMED, C. R. HELESKI, C. L. WICKENS and K. A.HOUPT

Abstract – Reasons for performing study: Crib-biting is an equine stereotypy that may result in diseases such as colic. Certain breeds and management factors have been associated. Objectives: To determine: breed prevalence of crib-biting in US horses; the likelihood that one horse learns to crib-bite from another; and owner perceptions of causal factors. Methods: An initial postal survey queried the number and breed of crib-biting horses and if a horse began after being exposed to a horse with this habit. In a follow-up survey, a volunteer subset of owners was asked the number of affected and nonaffected horses of each breed and the extent of conspecific contact. The likelihood of crib-biting given breed and extent of contact was quantified using odds ratio (OR) and significance of the association was assessed using the Chi-squared test. Results: Overall prevalence was 4.4%. Thoroughbreds were the breed most affected (13.3%). Approximately half of owners believed environmental factors predominantly cause the condition (54.4%) and crib-biting is learned by observation (48.8%). However, only 1.0% of horses became affected after being exposed to a crib-biter. The majority (86%) of horses was turned out in the same pasture with other horses and extent of contact with conspecifics was not statistically related to risk. Conclusion: This is the first study to report breed prevalence for crib-biting in US horses. Thoroughbreds were the breed more likely to be affected. More owners believed either environmental conditions were a predominant cause or a combination of genetic and environmental factors contributes to the behaviour. Only a small number of horses reportedly began to crib-bite after being exposed to an affected individual, but approximately half of owners considered it to be a learned behaviour; most owners did not isolate affected horses. Potential relevance: Genetic predisposition, not just intensive management conditions and surroundings, may be a factor in the high crib-biting prevalence in some breeds, and warrants further investigation. Little evidence exists to suggest horses learn the behaviour from other horses, and isolation may cause unnecessary stress.

Link – http://www3.interscience.wiley.com/journal/123230083/abstract

Exploring lay perceptions of the causes of crib-biting/windsucking behaviour in horses.

A. LITVA, C. S. ROBINSON and D. C. ARCHER

Abstract- Reasons for performing study: Crib-biting/windsucking behaviour has important consequences for equine health and welfare. Lay perceptions of health and illness are of interest to medical sociologists, providing important information to medical practitioners, but have infrequently been applied in veterinary research. Objectives: To demonstrate how lay epidemiology can be applied within veterinary research by exploring the lay perceptions regarding the causes of crib-biting/windsucking behaviour in horses. Methods: Informants were recruited from professional and amateur horse owners who had or had not owned/cared for a horse that exhibited crib-biting/windsucking behaviour. In-depth interviews were used to examine perceptions about the development of this behaviour within each group until a ‘saturation’ of themes emerged. Results: The main themes that emerged as causes of crib-biting/windsucking behaviour were ‘boredom’, ‘stress’ and ‘habit/addiction’. In the group of owners/carers who did not have direct experience of this type of behaviour, ‘copying’ from other horses emerged as a strong theme and they stated that they would not wish to own a crib-biting/windsucking horse. In contrast, those who had direct experience of horses demonstrating this behaviour did not believe copying was a cause based on their own observations and would not be put off purchasing or caring for another horse displaying this behaviour. Conclusions: Perceptions about what causes crib-biting/windsucking was influenced by whether or not informants had personal experience of horses demonstrating this behaviour. The three main themes that emerged have some justification based on current research and highlight the need for further investigation into the underlying pathophysiology of crib-biting/windsucking behaviour. Potential relevance: Qualitative approaches to health, disease and behaviour have an important role in the medical field and are applicable to veterinary research.

Link – http://www3.interscience.wiley.com/journal/123353793/abstract

Lateralised motor behaviour leads to increased unevenness in front feet and asymmetry in athletic performance in young mature Warmblood horses

C. van HEEL, M. C. van DIERENDONCK, A. M. KROEKENSTOEL and W. BACK

Abstract – Reason for performing study: Foot stance in grazing significantly influences hoof conformation and development from foal to yearling age.Objectives: To conduct a longitudinal study to establish if the relationship between motor laterality and uneven front feet persisted in 3-year-old horses at the time of studbook selection and to investigate if such laterality and unevenness might influence the horses’ ability to perform symmetrically while trotting, cantering and free jumping. Methods: Seventeen clinically sound but untrained (with only minimal experience of handling) and sound Warmblood horses that had participated in a previous study were assessed as per the protocol reported. Laterality was tested in a preference test (PT) and z-values were calculated for analysis purposes. Laterality and hoof unevenness were related to both relative limb length and relative head size, while the ability to perform symmetrically was tested in free trot-canter transitions and free jumping exercises. Differences in performance between horses with and without a limb preference in the PT and those with ‘uneven’ and ‘even’ feet were tested for differences in performance metrics using Students’ t test, while linearity was tested using a regression analysis (P<0.05). Results: Significant laterality was still present in 24% of the 3-year-old horses and the relationship between laterality and uneven feet pairs was stronger than at foal and yearling stages. Horses with significant motor laterality had almost 4 times more unevenness, a smaller head and longer limbs and the relationship between body conformation and laterality was still present. There was a strong linear relation between unevenness, laterality and a bias or side preference for trot-canter transitions. However, this relationship was not significant during the free jumping exercise. Conclusion: Motor laterality and uneven feet pairs were still present and significantly related in the 3-year-old horses and both variables were also strongly related to sidedness in trot-canter transitions. Potential relevance: Warmblood studbooks should include quantitative data on laterality at the time of studbook admission as part of the selection criteria.

Link – http://www3.interscience.wiley.com/journal/123339030/abstract

The Feral Horse

Affiliative relationships among Sorraia mares: influence of age, dominance, kinship and reproductive state

Filipa Heitor and Luís Vicente

Abstract – Affiliative relationships among mares were examined in a managed group of Sorraia horses, Equus caballus, over a 3-year period. We assessed the influence of age, dominance, kinship and reproductive state on the strength of affiliative relationships and diversity of partners. The herd comprised 9–11 mares that had known each other since birth, their foals and a stallion that remained in the group exclusively during the breeding season. In contrast to a previous study, kinship did not significantly affect bonds. Mares tended to spend more time in proximity to those in the same reproductive state. Affiliative relationships among mares were relatively stable but their strength decreased after foaling, possibly as a function of foal protection and bonding between dam and foal. There was no consistent evidence that mares disengaged from affiliative relationships with increasing age. As expected, dominant mares and barren mares contributed the most to affiliative relationships. Dominance rank increased with age, but dominance relationships were stable and did not change after foaling. Overall, reproductive state was the factor that had the most consistent influence on affiliative relationships among Sorraia mares.

Link – http://www.springerlink.com/content/n314557n16q646l4/

Dominance relationships and patterns of aggression in a bachelor group of Sorraia horses (Equus caballus)

Filipa Heitor and Luís Vicente

Abstract – The influence of individual factors on dominance rank and the relationship between rank distance and patterns of aggression predicted by models of evolutionarily stable strategies (ESS) of animal conflict were investigated in a managed bachelor group of Sorraia horses, Equus caballus. The group was composed of four to six stallions 3- to 12-years-old during the study period. The dominance hierarchy was significantly linear and rank was not related to age, weight, height or aggressiveness. Frequency and intensity of agonistic interactions were low, but higher-ranking stallions did not receive lower aggressiveness than lower-ranking stallions. There was some evidence that dominance relationships were more contested among close-ranking stallions, as predicted. Agonistic-related interactions among close-ranking stallions served similar functions to those among distant-ranking stallions, but the latter interacted more frequently than expected for access to resting sites and/or resting partners. Therefore, we found some evidence that agonistic-related interactions among distant-ranking stallions play a larger role in providing access to valuable and defendable resources than those among close-ranking stallions. Nevertheless, the fact that space to escape from aggression was limited and breeding access was independent from dominance rank may have reduced the benefits relative to costs of aggression and therefore limited the occurrence of contests over dominance and resources.

Link – http://www.springerlink.com/content/l67722831h4q302k/

Hope you enjoyed reading,

Emma Lethbridge

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