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A trained demonstrator has a calming effect on naïve horses when crossing a novel surface
Applied Animal Behaviour Science 171 (2015) 117–120
Contents lists available at ScienceDirect
Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim
A trained demonstrator has a calming effect on naïve horses when crossing a novel surface Maria Vilain Rørvang ∗ , Line Peerstrup Ahrendt, Janne Winther Christensen Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark
a r t i c l e
i n f o
Article history: Received 26 February 2015 Received in revised form 20 June 2015 Accepted 10 August 2015 Available online 22 August 2015 Keywords: Fear Habituation Social learning Social transmission Heart rate
a b s t r a c t Habituated horses have been found to have a calming effect on conspecifics in fear-eliciting situations. In practice, experienced horses are often used as companions when young horses are introduced to potentially frightening situations, like loading onto a trailer. However, studies of social transmission of habituation in horses are scarce. This study investigated if demonstration by a habituated demonstrator horse influenced the willingness of young Icelandic horses (n = 22, 3 years old) to cross a novel surface. Observer horses (n = 11) were allowed to observe the similarly aged demonstrator horse being led five times across a novel surface. Immediately afterwards the observer horses were given the opportunity to cross the novel surface themselves to obtain food on the other side. Controls (n = 11) were allowed to observe the demonstrator eating on the opposite side of the novel surface but not the demonstration of crossing the novel surface. All observers and controls succeeded the task, but observers had significantly lower average and maximum heart rate, compared to controls. This result suggests a calming effect of the demonstration, which could be exploited for habituation training of horses in fear-eliciting situations. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Fear reactions have definite survival value in wild animals, where the life expectancy depends on avoidance of potential dangers. Throughout domestication, animals´ı threshold for experiencing fear has been elevated, but when a fear-eliciting stimulus surpass this threshold domestic animals will show fear responses similar to their wild ancestors (Dwyer, 2004). In these situations, domestic horses can become dangerous to humans around them. Training domestic horses to react less in fear-provoking situations is, thus, of great importance to ensure safety in the horse-human relationship (Christensen et al., 2006). Habituation is a fundamental learning process, where the animal learns not to react towards specific stimuli (Rankin et al., 2009). Despite the importance of habituation in horse training, it has only been investigated scarcely (McGreevy and McLean, 2010). Some studies have shown that horses readily habituate to various stimuli (Christensen et al., 2008a, 2011), but that they tend to discriminate between stimuli with different appearance (Christensen et al., 2008a). Christensen et al. (2008b) found that a habituated horse had a calming effect on naïve conspecifics during exposure to a sudden stimulus. The
∗ Corresponding author. Tel.: +45 3135 1921. E-mail address: [email protected] (M.V. Rørvang). http://dx.doi.org/10.1016/j.applanim.2015.08.008 0168-1591/© 2015 Elsevier B.V. All rights reserved.
naïve test horses with habituated companions showed reduced fear reactions and had lower heart rates during the test, compared to controls with non-habituated companions, and, perhaps more importantly, the effects were persistent even when the naïve horses were exposed to the same stimulus alone 3 days later. Similar results have also been shown with heifers by Boissy and Le Neindre (1990), who found that heifers with habituated companions reacted less to frightening stimuli than heifers accompanied by stressed companions. In practice, older and trained horses are also often used in various situations to calm younger horses e.g. when loading onto a trailer (McGreevy and McLean, 2010). The majority of studies investigating social learning in horses in more complex situations, such as discriminating between differently coloured buckets and opening boxes to obtain food, have however, failed to find evidence of social learning (Baer et al., 1983; Baker and Crawford, 1986; Clarke et al., 1996; Lindberg et al., 1999; Ahrendt et al., 2012). It has been argued that the more complex situations have less biological relevance than frightening situations, and social learning may therefore be less likely to occur in complex learning designs (Nicol, 2002). In this study, we included a potentially frightening situation in a traditional social learning experimental design. The situation consisted of crossing a novel surface, which generally induces fear in horses (Visser et al., 2001; Lansade et al., 2008). The naïve observer horses observed from a distance when the trained demonstrator crossed the novel surface,
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M.V. Rørvang et al. / Applied Animal Behaviour Science 171 (2015) 117–120
before being allowed to solve the task themselves. This set-up differed from the set-up in e.g. Christensen et al. (2008b) where the horses were together during the demonstrations. The new set-up required that observer horses were able to perceive, retain and use the information from the demonstration. We hypothesised observer horses would show reduced fear responses (i.e. cross the novel surface faster and have lower heart rates), compared to control horses, which were not exposed to prior demonstration. 2. Materials and methods 2.1. Animals 24 Icelandic horses (3 years old) participated in the study. The horses were privately owned and had been raised in loose housing systems receiving only routine management training. The horses arrived at the research facility two months before the experiment, where they were pastured 24 h/day in two herds (mares (n = 12) and geldings (n = 12)). Both pastures (5 ha of clover/grass mixture each) had ad libitum access to water, roughage, minerals and shelter (30 m2 ). 2.2. Stable and habituation process Before initiating the experiment all horses were gradually habituated to being led into the stable, having heart rate equipment fastened with an elastic girth as well as to social isolation in the test arena. In the test arena (20 m × 18 m), the horses were allowed to feed from a black feed bucket (Ø: 0.5 m, height: 0.3 m; containing alfalfa and cracked maize with molasses), which was later used in the test situation. The habituation procedure was complete when all horses voluntarily walked directly to the feed bucket when released in the test arena.
linen in the opening). Then the test horses were divided into two groups balanced according to gender. The groups were then randomly assigned as either observer (n = 11) or control (n = 11). All horses were tested on the same day in a random order, alternating between observers and controls.
2.5.1. Test procedure for observer horses The demonstrator and observer horse were led into the arena together. Both horses were placed at the starting point (approx. 10 m from the linen). The demonstration consisted of the demonstrator horse being led across the linen 5 times by the human handler. Every time the demonstrator was on the side with the feed buckets it was allowed to eat one mouthful from the test bucket, before being led back across the linen. After the demonstration the demonstrator was led from the test bucket to the other feed bucket, where it remained during the test (Fig. 1). The observer was then released from the starting point and had 1 min to cross the linen and thereby succeed the task. The linen was considered crossed when all four legs were on the opposite side. If the observer did not solve the task within 1 min it was caught, returned to the starting point and released for a new trial, without any further demonstration. Each observer was allowed three trials to solve the task.
2.5.2. Test procedure for control horses The demonstrator was led into the arena and placed at the test bucket. The control was then led into the arena and placed at the starting point. The control remained at the starting point for 90 s, corresponding to the duration of the demonstration for observers, i.e. control horses were able to see the demonstrator horse eating from the test bucket but did not see the demonstrator walking across the linen. The control horse was then released and had three 1-min trials to solve the task, similarly to the observer horses.
2.3. Test design The test arena was divided in two areas separated by a fence, which had a 4 m wide opening in the middle (Fig. 1). During the test, a white linen (1.5 m × 4 m) was placed on the ground in the opening. Thus, the horses were required to step on the linen to get to the feed buckets on the opposite side of the fence. Two feed buckets were available to minimise possible aggression arising from demonstrator and test horse sharing one feed bucket. 2.4. Demonstrator horses Since the social status of the demonstrator animal may affect the level of attention from the observers (Nicol and Pope, 1994a,b), we chose socially dominant demonstrators (one from each herd to ensure that the demonstrator horse was familiar to the observers). The dominance hierarchy in each herd was determined through 48 h of behavioural recordings (displacements, aggression, mounting, social play and social grooming) at pasture and a limited resource test (Rørvang, 2013). Prior to testing, both demonstrators were trained to walk calmly across the novel surface. The demonstrators were trained two days with on average 10 (±4) repetitions of gradually approaching and crossing the linen. A handler led the demonstrators during the demonstrations to ensure that they would cross the surface similarly during every demonstration, stay in approximately the same position when eating, and to minimise aggression. 2.5. Test procedure All test horses were first trained to walk straight through the opening in the fence, without the linen (Fig. 1, but without the
2.6. Recordings and statistical methods Latencies to succeed the task were recorded as time from release to accomplishment of the task. Heart rate (HR) was recorded (R–R recordings) using Polar Equine RS800cx (Polar Electro OY, Kemple, Finland), consisting of an Equine Wearlink with a W.I.N.D. transmitter and a wristwatch receiver. Water and gel were used to optimise the contact between electrode and skin. Data from the wristwatch receiver was downloaded using the software Polar ProTrainer, Equine Edition 5TM . Artefacts in the data were corrected using the error correction function in this programme. Data was calculated as average and max HR during the test (beats per minute (bpm)). Although the recordings allowed analysis of heart rate variability (HRV) this was not included due to the very short latency to succeed the task; HRV should be recorded for at least 5 min to provide a valid measure (von Borell et al., 2007). Latencies and HR (average and maximum) were visually evaluated to be normally distributed, and were, thus, analysed using a Welch two-sample ttest using the statistical software “R” (R version 3.0.2., R Core Team, 2013), and evaluated using a significance level of 5%.
2.7. Results All controls and observers managed to cross the linen in their first trial and thus there was no treatment difference in the success rate. Observer horses had, however, significantly lower heart rates (Fig. 2), even though there was no difference in the latency to succeed the task (Welch two-sample t-test: (s, mean ± s.e.) Observer: 14.8 ± 4.3 vs. Control: 11.3 ± 5.0, P = 0.38).
M.V. Rørvang et al. / Applied Animal Behaviour Science 171 (2015) 117–120
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Fig. 1. Experimental setup for the test. The hooves illustrate the route, which was demonstrated to the observer horses. The horse illustrates the proximate position of the demonstrator during the test. The white square illustrates the white linen.
Fig. 2. Average and maximum heart rate for control and observer horses (**P < 0.01, *P < 0.05).
3. Discussion The results in the present study showed that prior demonstration of crossing a novel surface led to reduced average and maximum heart rates in observer horses. These results support the findings by Christensen et al. (2008b) and shows that the calming effect can also occur when observation is made from a distance and with a short delay (10 s) between demonstration and test. It should
be noted, however, that the results of the present study are based on a limited number of animals and further studies of this potentially calming effect of a demonstrator are warranted. The treatment difference in heart rates was not reflected in the success rate and latency, suggesting that the intensity of the task was too low for these Icelandic horses. The fear stimulus in this experiment was chosen based on previous results with similarly aged Danish Warmblood horses (Christensen et al., 2011). In that study, 48% of the horses (n = 25) did not step on the linen within a 3-min test time and the test stimulus was replaced by a less frightening task. This is moreover supported by the heart rate data from the study (HR max (bpm), mean ± s.e.: Danish Warmblood: 106 ± 4.7 (unpublished data) vs. Icelandic horses in this study: Observers: 86.2 ± 3.6 and controls: 93.8 ± 5.1). Breed differences in fearfulness have previously been documented, where cold-blooded horses seem to be less fearful compared to warmblood horses (Bagshaw et al., 1994; Górecka-Bruzda et al., 2011). Although several studies emphasise breed differences in behavioural tests (e.g. reviewed by Hausberger and Richard-Yris in 2005) there are only few studies including a sufficient number of horses of different breeds to actually investigate for breed differences. This information may be of both scientific and practical value, when horses are selected for specific purposes, but remains to be studied further. Despite the lack of treatment differences in success rate and latency to succeed, the heart rate differences suggest that using a frightening task may be more relevant to detect social learning in horses, compared to the previously used operant tasks (e.g. Clarke et al., 1996; Lindberg et al., 1999; Ahrendt et al., 2012), or spatial tasks (Rørvang et al., 2015). It would be valuable to repeat this study
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with warmblood horses and to investigate if a stronger fear stimulus could lead to a treatment difference in success rate and latency to succeed in Icelandic horses. 4. Conclusions This small-scale study found that horses observing a calm demonstrator horse crossing a novel surface had significantly lower heart rates when solving the task themselves, compared to control horses with no prior demonstration. The success rate and the latency to succeed was unaffected by social demonstrations, possibly because the stimulus intensity was too low. Our results support the use of a calm demonstrator horse when naive horses are introduced to potentially frightening situations. Conflicts of interest The authors declare that there are no conflicts of interest. Acknowledgements We thank Anna Feldberg Marsbøll and Emeline Cornet for assistance during the experiment. A special thanks to the horse owners for kindly allowing us to use their horses. References Ahrendt, L.P., Christensen, J.W., Ladewig, J., 2012. The ability of horses to learn an instrumental task through social observation. Appl. Anim. Behav. Sci. 139, 105–113. Baer, K.L., Potter, G.D., Friend, T.H., Beaver, B.V., 1983. Observation effects on learning behaviour in horses. Appl. Anim. Ethol. 11, 123–129. Bagshaw, C.S., Ralston, S.L., Fisher, H., 1994. Behavioural and physiological effects of orally administered tryptophan on horses subjected to acute isolation stress. Appl. Anim. Behav. Sci. 40, 1–12. Baker, A.E.M., Crawford, B.H., 1986. Observational learning in horses. Appl. Anim. Ethol. 15, 7–13. Boissy, A., Le Neindre, P., 1990. Social influences on the reactivity of heifers: Implications for learning abilities on operant conditioning. Appl. Anim. Behav. Sci. 25, 149–165. Christensen, J.W., Rundgren, M., Olsson, K., 2006. Training methods for horses: habituation to a frightening stimulus. Equin. Vet. J. 38, 439–443.
Christensen, J.W., Zharkikh, T., Ladewig, J., 2008a. Do horses generalise between objects during habituation? Appl. Anim. Behav. Sci. 114, 509–520. Christensen, J.W., Malmkvist, J., Nielsen, B.L., Keeling, L.J., 2008b. Effects of a calm companion on fear reactions in naive test horses. Equin. Vet. J. 40, 46–50. Christensen, J.W., Zharkikh, T., Chovaux, E., 2011. Object recognition and generalisation during habituation in horses. Appl. Anim. Behav. Sci. 129, 83–91. Clarke, J.V., Nicol, C.J., Jones, R., McGreevy, P.D., 1996. Effects of observational learning on food selection in horses. Appl. Anim. Behav. Sci. 50, 177–184. Dwyer, C.M., 2004. How has the risk of predation shaped the behavioural responses of sheep to fear and distress? Anim. Welf. 13, 269–281. Górecka-Bruzda, A., Jastrzebska, E., Sosnowska, Z., Jaworski, Z., Jezierski, T., Chruszczewski, M.H., 2011. Reactivity to humans and fearfulness tests: field validation in Polish cold blood horses. Appl. Anim. Behav. Sci. 133, 207–215. Hausberger, M., Richard-Yris, M.A., 2005. Individual differences in the domestic horse, origins, development and stability. In: Mills, D., McDonnel, S. (Eds.), The Domestic Horse. Evolution, Development and Management of its Behaviour. Cambridge University Press, Cambridge, pp. 32–52. Lansade, L., Bouissou, M.-F., Erhard, H.W., 2008. Fearfulness in horses: a temperament trait stable across time and situations. Appl. Anim. Behav. Sci. 115, 182–200. Lindberg, A.C., Kelland, A., Nicol, C.J., 1999. Effects of observational learning on acquisition of an operant response in horses. Appl. Anim. Behav. Sci. 61, 187–199. McGreevy, P., McLean, A., 2010. Equitation Science. Wiley-Blackwell, Chichester, UK, pp. 328. Nicol, C.J., 2002. Equine learning: progress.and suggestions for future research. Appl. Anim. Behav. Sci. 78, 193–208. Nicol, C.J., Pope, S.J., 1994a. Social learning in small flocks of laying hens. Anim. Behav. 47, 1289–1296. Nicol, C.J., Pope, S.J., 1994b. Social learning in sibling pigs. Appl. Anim. Behav. Sci. 40, 31–43. Rankin, C.H., Abrams, T., Barry, R.J., 2009. Habituation revisited: an updated and revised description of the behavioural characteristics of habituation. Neurobiol. Learn. Mem. 92, 135–138. R Core Team, 2013. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria, URL: http://www.r-project.org/. Rørvang, M.V., Ahrendt, L.P., Christensen, J.W., 2015. Horses fail to use social learning when solving spatial detour tasks. Anim. Cogn. 18, 847–854. Rørvang, M.V., 2013. Hierarchy Formation and Stability in Young Icelandic Horses. Aarhus University (Project report). Visser, E.K., van Reenen, C.G., Hopster, H., Schilder, M.B.H., Knaap, J.H., Barneveld, A., Blokhuis, H.J., 2001. Quantifying aspects of young horses’ temperament: consistency of behavioural variables. Appl. Anim. Behav. Sci. 74, 241–258. von Borell, E., Langbein, J., Després, G., Hansen, S., Leterrier, C., Marchant-Fonde, J., Marchant-Fonde, R., Minero, M., Mohr, E., Prunier, A., Valance, D., Veissier, I., 2007. Heart rate variability as a measure of autonomic regulation of cardiac activity for assessing stress and welfare in farm animals – a review. Physiol. Behav. 92, 293–316.
Contents lists available at ScienceDirect
Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim
A trained demonstrator has a calming effect on naïve horses when crossing a novel surface Maria Vilain Rørvang ∗ , Line Peerstrup Ahrendt, Janne Winther Christensen Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark
a r t i c l e
i n f o
Article history: Received 26 February 2015 Received in revised form 20 June 2015 Accepted 10 August 2015 Available online 22 August 2015 Keywords: Fear Habituation Social learning Social transmission Heart rate
a b s t r a c t Habituated horses have been found to have a calming effect on conspecifics in fear-eliciting situations. In practice, experienced horses are often used as companions when young horses are introduced to potentially frightening situations, like loading onto a trailer. However, studies of social transmission of habituation in horses are scarce. This study investigated if demonstration by a habituated demonstrator horse influenced the willingness of young Icelandic horses (n = 22, 3 years old) to cross a novel surface. Observer horses (n = 11) were allowed to observe the similarly aged demonstrator horse being led five times across a novel surface. Immediately afterwards the observer horses were given the opportunity to cross the novel surface themselves to obtain food on the other side. Controls (n = 11) were allowed to observe the demonstrator eating on the opposite side of the novel surface but not the demonstration of crossing the novel surface. All observers and controls succeeded the task, but observers had significantly lower average and maximum heart rate, compared to controls. This result suggests a calming effect of the demonstration, which could be exploited for habituation training of horses in fear-eliciting situations. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Fear reactions have definite survival value in wild animals, where the life expectancy depends on avoidance of potential dangers. Throughout domestication, animals´ı threshold for experiencing fear has been elevated, but when a fear-eliciting stimulus surpass this threshold domestic animals will show fear responses similar to their wild ancestors (Dwyer, 2004). In these situations, domestic horses can become dangerous to humans around them. Training domestic horses to react less in fear-provoking situations is, thus, of great importance to ensure safety in the horse-human relationship (Christensen et al., 2006). Habituation is a fundamental learning process, where the animal learns not to react towards specific stimuli (Rankin et al., 2009). Despite the importance of habituation in horse training, it has only been investigated scarcely (McGreevy and McLean, 2010). Some studies have shown that horses readily habituate to various stimuli (Christensen et al., 2008a, 2011), but that they tend to discriminate between stimuli with different appearance (Christensen et al., 2008a). Christensen et al. (2008b) found that a habituated horse had a calming effect on naïve conspecifics during exposure to a sudden stimulus. The
∗ Corresponding author. Tel.: +45 3135 1921. E-mail address: [email protected] (M.V. Rørvang). http://dx.doi.org/10.1016/j.applanim.2015.08.008 0168-1591/© 2015 Elsevier B.V. All rights reserved.
naïve test horses with habituated companions showed reduced fear reactions and had lower heart rates during the test, compared to controls with non-habituated companions, and, perhaps more importantly, the effects were persistent even when the naïve horses were exposed to the same stimulus alone 3 days later. Similar results have also been shown with heifers by Boissy and Le Neindre (1990), who found that heifers with habituated companions reacted less to frightening stimuli than heifers accompanied by stressed companions. In practice, older and trained horses are also often used in various situations to calm younger horses e.g. when loading onto a trailer (McGreevy and McLean, 2010). The majority of studies investigating social learning in horses in more complex situations, such as discriminating between differently coloured buckets and opening boxes to obtain food, have however, failed to find evidence of social learning (Baer et al., 1983; Baker and Crawford, 1986; Clarke et al., 1996; Lindberg et al., 1999; Ahrendt et al., 2012). It has been argued that the more complex situations have less biological relevance than frightening situations, and social learning may therefore be less likely to occur in complex learning designs (Nicol, 2002). In this study, we included a potentially frightening situation in a traditional social learning experimental design. The situation consisted of crossing a novel surface, which generally induces fear in horses (Visser et al., 2001; Lansade et al., 2008). The naïve observer horses observed from a distance when the trained demonstrator crossed the novel surface,
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before being allowed to solve the task themselves. This set-up differed from the set-up in e.g. Christensen et al. (2008b) where the horses were together during the demonstrations. The new set-up required that observer horses were able to perceive, retain and use the information from the demonstration. We hypothesised observer horses would show reduced fear responses (i.e. cross the novel surface faster and have lower heart rates), compared to control horses, which were not exposed to prior demonstration. 2. Materials and methods 2.1. Animals 24 Icelandic horses (3 years old) participated in the study. The horses were privately owned and had been raised in loose housing systems receiving only routine management training. The horses arrived at the research facility two months before the experiment, where they were pastured 24 h/day in two herds (mares (n = 12) and geldings (n = 12)). Both pastures (5 ha of clover/grass mixture each) had ad libitum access to water, roughage, minerals and shelter (30 m2 ). 2.2. Stable and habituation process Before initiating the experiment all horses were gradually habituated to being led into the stable, having heart rate equipment fastened with an elastic girth as well as to social isolation in the test arena. In the test arena (20 m × 18 m), the horses were allowed to feed from a black feed bucket (Ø: 0.5 m, height: 0.3 m; containing alfalfa and cracked maize with molasses), which was later used in the test situation. The habituation procedure was complete when all horses voluntarily walked directly to the feed bucket when released in the test arena.
linen in the opening). Then the test horses were divided into two groups balanced according to gender. The groups were then randomly assigned as either observer (n = 11) or control (n = 11). All horses were tested on the same day in a random order, alternating between observers and controls.
2.5.1. Test procedure for observer horses The demonstrator and observer horse were led into the arena together. Both horses were placed at the starting point (approx. 10 m from the linen). The demonstration consisted of the demonstrator horse being led across the linen 5 times by the human handler. Every time the demonstrator was on the side with the feed buckets it was allowed to eat one mouthful from the test bucket, before being led back across the linen. After the demonstration the demonstrator was led from the test bucket to the other feed bucket, where it remained during the test (Fig. 1). The observer was then released from the starting point and had 1 min to cross the linen and thereby succeed the task. The linen was considered crossed when all four legs were on the opposite side. If the observer did not solve the task within 1 min it was caught, returned to the starting point and released for a new trial, without any further demonstration. Each observer was allowed three trials to solve the task.
2.5.2. Test procedure for control horses The demonstrator was led into the arena and placed at the test bucket. The control was then led into the arena and placed at the starting point. The control remained at the starting point for 90 s, corresponding to the duration of the demonstration for observers, i.e. control horses were able to see the demonstrator horse eating from the test bucket but did not see the demonstrator walking across the linen. The control horse was then released and had three 1-min trials to solve the task, similarly to the observer horses.
2.3. Test design The test arena was divided in two areas separated by a fence, which had a 4 m wide opening in the middle (Fig. 1). During the test, a white linen (1.5 m × 4 m) was placed on the ground in the opening. Thus, the horses were required to step on the linen to get to the feed buckets on the opposite side of the fence. Two feed buckets were available to minimise possible aggression arising from demonstrator and test horse sharing one feed bucket. 2.4. Demonstrator horses Since the social status of the demonstrator animal may affect the level of attention from the observers (Nicol and Pope, 1994a,b), we chose socially dominant demonstrators (one from each herd to ensure that the demonstrator horse was familiar to the observers). The dominance hierarchy in each herd was determined through 48 h of behavioural recordings (displacements, aggression, mounting, social play and social grooming) at pasture and a limited resource test (Rørvang, 2013). Prior to testing, both demonstrators were trained to walk calmly across the novel surface. The demonstrators were trained two days with on average 10 (±4) repetitions of gradually approaching and crossing the linen. A handler led the demonstrators during the demonstrations to ensure that they would cross the surface similarly during every demonstration, stay in approximately the same position when eating, and to minimise aggression. 2.5. Test procedure All test horses were first trained to walk straight through the opening in the fence, without the linen (Fig. 1, but without the
2.6. Recordings and statistical methods Latencies to succeed the task were recorded as time from release to accomplishment of the task. Heart rate (HR) was recorded (R–R recordings) using Polar Equine RS800cx (Polar Electro OY, Kemple, Finland), consisting of an Equine Wearlink with a W.I.N.D. transmitter and a wristwatch receiver. Water and gel were used to optimise the contact between electrode and skin. Data from the wristwatch receiver was downloaded using the software Polar ProTrainer, Equine Edition 5TM . Artefacts in the data were corrected using the error correction function in this programme. Data was calculated as average and max HR during the test (beats per minute (bpm)). Although the recordings allowed analysis of heart rate variability (HRV) this was not included due to the very short latency to succeed the task; HRV should be recorded for at least 5 min to provide a valid measure (von Borell et al., 2007). Latencies and HR (average and maximum) were visually evaluated to be normally distributed, and were, thus, analysed using a Welch two-sample ttest using the statistical software “R” (R version 3.0.2., R Core Team, 2013), and evaluated using a significance level of 5%.
2.7. Results All controls and observers managed to cross the linen in their first trial and thus there was no treatment difference in the success rate. Observer horses had, however, significantly lower heart rates (Fig. 2), even though there was no difference in the latency to succeed the task (Welch two-sample t-test: (s, mean ± s.e.) Observer: 14.8 ± 4.3 vs. Control: 11.3 ± 5.0, P = 0.38).
M.V. Rørvang et al. / Applied Animal Behaviour Science 171 (2015) 117–120
119
Fig. 1. Experimental setup for the test. The hooves illustrate the route, which was demonstrated to the observer horses. The horse illustrates the proximate position of the demonstrator during the test. The white square illustrates the white linen.
Fig. 2. Average and maximum heart rate for control and observer horses (**P < 0.01, *P < 0.05).
3. Discussion The results in the present study showed that prior demonstration of crossing a novel surface led to reduced average and maximum heart rates in observer horses. These results support the findings by Christensen et al. (2008b) and shows that the calming effect can also occur when observation is made from a distance and with a short delay (10 s) between demonstration and test. It should
be noted, however, that the results of the present study are based on a limited number of animals and further studies of this potentially calming effect of a demonstrator are warranted. The treatment difference in heart rates was not reflected in the success rate and latency, suggesting that the intensity of the task was too low for these Icelandic horses. The fear stimulus in this experiment was chosen based on previous results with similarly aged Danish Warmblood horses (Christensen et al., 2011). In that study, 48% of the horses (n = 25) did not step on the linen within a 3-min test time and the test stimulus was replaced by a less frightening task. This is moreover supported by the heart rate data from the study (HR max (bpm), mean ± s.e.: Danish Warmblood: 106 ± 4.7 (unpublished data) vs. Icelandic horses in this study: Observers: 86.2 ± 3.6 and controls: 93.8 ± 5.1). Breed differences in fearfulness have previously been documented, where cold-blooded horses seem to be less fearful compared to warmblood horses (Bagshaw et al., 1994; Górecka-Bruzda et al., 2011). Although several studies emphasise breed differences in behavioural tests (e.g. reviewed by Hausberger and Richard-Yris in 2005) there are only few studies including a sufficient number of horses of different breeds to actually investigate for breed differences. This information may be of both scientific and practical value, when horses are selected for specific purposes, but remains to be studied further. Despite the lack of treatment differences in success rate and latency to succeed, the heart rate differences suggest that using a frightening task may be more relevant to detect social learning in horses, compared to the previously used operant tasks (e.g. Clarke et al., 1996; Lindberg et al., 1999; Ahrendt et al., 2012), or spatial tasks (Rørvang et al., 2015). It would be valuable to repeat this study
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