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Laterality in stride pattern preferences in racehorses
ANIMAL BEHAVIOUR, 2007, 74, 941e950 doi:10.1016/j.anbehav.2007.01.014
Laterality in stride pattern preferences in racehorses D. E. WILLIAMS* & B . J. NOR RIS †
*Department of Forest, Rangeland, and Watershed Stewardship, Warner College of Natural Resources, 120 Forestry Bldg, Colorado State University, Fort Collins, U.S.A. yDepartment of Biological Sciences, California State University, San Marcos (Received 14 July 2006; initial acceptance 18 August 2006; final acceptance 15 January 2007; published online 19 September 2007; MS. number: A10512R)
During performance, racehorses gallop in an asymmetrical stride with either the left hindhoof striking the ground first (right lead stride pattern) or the right hindhoof striking the ground first (left lead stride pattern). In this study we examined racehorses for a stride pattern preference. Here, we showed that racehorses do have a preference for one stride pattern over the other. Across thoroughbreds, Arabians, and American Quarter horses 90% preferred their right lead stride pattern with 10% preferring the left. In a repeated studies test, a single racehorse consistently preferred one stride pattern over the other. We further showed that stride pattern preference is reflected in stride pattern usage during a 6-furlong morning workout. Horses will run in their preferred stride pattern unless forced to switch while turning, injured, or fatigued (at the end of the race). Finally, we showed that in a small sample, there were minor variations between the right and left lead stride patterns. Because running is intimately linked to respiration in performing racehorses, stride pattern preference might contribute to performance in racehorses. Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Keywords: Equus caballus; laterality; racehorse; stride
Until recently, laterality or handedness, a preferential usage of one side of the body was studied almost exclusively in humans. In more recent years, laterality has been shown to be a widespread phenomenon in a number of vertebrate species (for recent reviews see Bisazza et al. 1997; Rogers & Andrew 2002). Laterality at either the individual or population level has been observed across a wide range of vertebrates including fish (Bisazza et al. 1997, 2000), amphibians (Robins & Rogers 2004), reptiles (Roth 2003; Hews et al. 2004), birds (Casey 2005; Ventolini et al. 2005) and mammals other than primates (Glick & Ross 1981; Cowell et al. 1997; Wells 2003; Schwarting & Borta 2005). It has even been observed in invertebrates (Ades & Ramires 2002; Byrne et al. 2004). These results and others suggest that lateralization is a phenomenon that probably arose early in vertebrate evolution (Vallortigara & Bisazza 2002). In this study we wanted to look for laterality in the racehorse (Equus caballus). Laterality in racehorses is of particular importance because several authors have Correspondence and present address: B. J. Norris, Department of Biological Sciences, CSUSM, San Marcos, CA 92096, U.S.A. (email: [email protected]). D. E. Williams is now at the 222 East View Street, Fallbrook, CA 92028, U.S.A. 0003e 3472/07/$30.00/0
suggested that a laterality bias might affect performance (McGreevy & Rogers 2005; Larose et al. 2006). When a horse is running, it tends to use a stride pattern known as the asymmetrical transverse gallop gait (Hildebrand 1977; Budiansky 1997). This gait consists of two phases: (1) the stance phase when one or more of the horse’s hooves are on the ground; and (2) the suspension phase when the horse is completely airborne (Muybridge 1899). The stance phase is asymmetrical (Adams 1979) with either the right forehoof (right lead stride pattern, RLSP) or the left forehoof (left lead stride pattern, LLSP) touching the ground last (Fig. 1). In the tracks on the ground, the hoof to touch last is in the ‘Lead’. There are distinct differences between the functions of the left and right hooves during asymmetrical gallop gait (Deuel & Lawrence 1987; Drevemo et al. 1987). If the left side and the right side are used slightly differently during the gallop, then laterality might enhance performance if a horse can perform in its preferred stride pattern. When a horse is running, there is a direct link between breathing and galloping with exactly one breath/stride (Hoyt & Taylor 1981). Because of biomechanical constraints, the horse exhales while in the stance phase and inhales while in the suspension phase. Given the direct link between stride pattern and breathing, the possibility exists that
941 Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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ANIMAL BEHAVIOUR, 74, 4
(a)
(b)
LR(1)
LF(3)
RR(2)
LF(4)
LR(2)
RF(4)
RR(1)
RF(3)
Figure 1. Photographs of racehorses in their (a) right lead stride pattern (RLSP) and (b) left lead stride pattern (LLSP). The stride patterns are named for the hoofprints left on the ground, which are shown schematically below each horse. Numbers in parentheses indicate the sequence in which the hooves contact the ground.
a preference for one stride pattern over the other may be linked to performance. Any or all of these factors might combine to give racehorses a preference when running in the asymmetrical gallop. If racehorses display laterality, then running efficiency might vary with lead stride pattern. Recently, there have been several important studies examining laterality in the domestic horse. Deuel & Lawrence (1987) used high-speed cinematography to examine the gallop in American Quarter horses. Although their study involved only four horses, they were able to show that these horses displayed a preference for galloping in their left lead. They were also able to document differences between the left lead and right lead stride patterns. Murphy et al. (2005) also observed laterality in the motor activities of horses. They observed whether horses preferred initiating movement from a standing start with their right leg or left leg. They further observed whether horses preferred passing an obstacle on their left or right under different circumstances. Across all horses tested, there was significant lateralization in that most horses consistently preferred either their right or left side. However, the numbers that preferred the right were not significantly different from the numbers that preferred the left. These results suggest that for the properties measured, horses display laterality at the individual level, but not at the population level. However, when they compared the results based on sex, a significant populationlevel difference was observed in that females displayed significantly more right lateralized responses while males were significantly more left lateralized. McGreevy & Rogers (2005) looked at both motor and sensory laterality in thoroughbreds. When observing whether horses stood with their right limb or left limb advanced, they observed that amongst horses that had a preference, more horses
preferred their left limb. They also observed that preference was stronger in older horses. When the population as a whole was compared, there was a significant left advanced preference. They also examined nostril preference when investigating an interesting olfactory stimulus (stallion faeces). Younger horses showed a significant right nostril bias, but older horses showed no bias. Interestingly, there was no correlation in motor and sensory bias in horses that were tested for both. Finally, Larose et al. (2006) tested whether two breeds of horses preferred to examine a novel stimulus with their right or left eye as well as their right or left nostril. Although there was no significant laterality observed across all horses, there was a correlation between the emotionality of the novel stimulus (as indicated by the horses’ behaviour) and a tendency to view the novel stimulus with the left eye. Taken together, these studies indicate that while horses may show laterality at the individual level, there is little evidence for laterality at the population level. When breaking into a run from a standing start or when transitioning from a trot to a gallop, a racehorse must decide which lead stride pattern to use. Although racehorses are constrained to using their inside lead around turns (LLSP when running anticlockwise around a track; Adams 1979), they have a choice as to which lead to use on straight sections of the track. In this study, we hypothesized that racehorses have a preference for either their right or left lead stride pattern. We tested this by observing racehorses as they began running from a standing start (breaking from the starting gate) and while making the trot-to-gallop transition. We made repeated observations to test stride pattern preference consistency within individual racehorses. We also monitored stride selection during a 6-furlong run. Finally, we compared LLSP and RLSP within individual horses to look for consistent variation
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
between the two stride patterns. If racehorses have a preferred stride pattern, it might in turn influence a horse’s ability to run races at various distances (i.e. sprints that are normally run around one turn, distance races running around two turns; the full track).
METHODS
Animals A total of 9362 horses were observed during the course of the study. Animals observed included thoroughbreds, Arabians, and American Quarter horses. All animals were observed in the U.S.A., where horses race around an oval racetrack in an anticlockwise direction. Because training to race in a particular direction might influence stride pattern preference, American Quarter horses, which race in a straight line, serve as an internal control. The horses were not experimentally manipulated in any way. Observations were made on horses during normal training sessions and while breaking from the gate during races.
Lead Stride Pattern Preference Trot-to-gallop transition During warm-up for morning training sessions, 209 racehorses were observed making the trot-to-gallop transition, and the gender and lead stride pattern of the transverse gallop gait was observed and recorded. If the horse’s left front limb was in the lead position during the first gallop stride from the trot-to-gallop transition, and continued in the same lead, the horse was recorded as using the left lead stride pattern (LLSP). All thoroughbreds were observed at San Luis Rey Downs Training Center in Bonsall, California. All American Quarter horses and Arabian racehorses were observed at Los Alamitos Race Course in Cypress, California. All observations were carried out during one morning training session to rule out the possibility of recording the same horse twice. Only transitions occurring on straight sections of the track were recorded to rule out the possibility of stride pattern preference for turn negotiation benefit.
Breaking from the starting gate When performing, a racehorse starts the race from the standing position in the starting gate. When the horse was observed to break from the starting gate leading with the left forelimb, the horse was recorded as using a left lead stride pattern (Fig. 2). A total of 9116 horses were observed. Video replay examinations were used from Los Alamitos Race Course, in Cypress, California, for the American Quarter horse and the Arabian racehorses. Video replay examinations for the thoroughbred racehorses were used from Del Mar, Hollywood Park, and Santa Anita racetracks in southern California. An additional 85 horses were observed breaking from the starting gate in racetracks in Hong Kong and Australia. These horses race clockwise around the racetrack (as opposed to anticlockwise in U.S.A.) and serve as a further control that stride pattern preferences are not ‘trained’.
Multiple observations from individual racehorses To test whether racehorses consistently express a stride pattern preference, we carried out multiple observations of particular racehorses. We examined video replays of thoroughbred racehorses that were stabled at San Luis Rey Downs Training Center in Bonsall, California and participated in races at southern California racetracks. Stride patterns of 32 horses were recorded during five to seven races for a repeated studies examination.
Statistical Analysis We tested for laterality at the population level for both the trot-to-gallop transition and while breaking from the starting gate. To do this, we calculated a mean proportion of RLSP: RLSP/(RLSP þ LLSP) from each of the six different categories (thoroughbred males, thoroughbred females, Arabian males, Arabian females, American Quarter horse males, American Quarter horse females). Because the categories did not contain equal numbers of observations, we converted the number of observations to proportions for analysis. We used a one-value t test to determine whether the proportion of RLSP horses was significantly different from 0.5 (RLSP ¼ LLSP).
Figure 2. Photograph of nine horses breaking from the starting gate. Eight of the nine horses are in their right lead stride pattern (RLSP) and one is in the left lead stride pattern (LLSP). Note particularly the no. 9 horse in its RLSP and the no. 2 horse in its LLSP.
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ANIMAL BEHAVIOUR, 74, 4
To test for differences based on breed or sex for both the trot-to-gallop transition and breaking from the starting gate, a standard chi-square analysis was used. The percentage of all horses starting in their RLSP for all observations was calculated. This total percentage was used to calculate the expected number of RLSP horses in each of the six categories. The chi-square analysis was used to test whether the observed deviated from the expected in each category. To test for laterality at the individual level, we calculated a laterality index (LI) for each of the 32 horses used in the repeated measures study. The LI was calculated as (RLSP LLSP)/(RLSP þ LLSP)100. If the number of starts in the RLSP is equal to the number of starts in the LLSP, the LI will equal 0. To test for laterality without regard to side, we calculated the mean and standard error for the absolute value of LI for all 32 horses. We then used a one-value t test to determine whether that mean was significantly different from 0. We also examined whether left-lead preferring horses were as likely to start a race in their preferred lead as right-lead preferring horses were. To do this, we calculated the mean of the absolute value of LI for horses that started primarily in their left lead and for horses that started primarily in their right lead. The two means were compared using a ManneWhitney U test.
Stride Pattern Selection during a 6-Furlong Morning Workout Because of the difficulty in counting strides and stride changes of an individual horse during an actual race, 12 thoroughbred racehorses were tested during the course of a 6-furlong morning workout on a standard 1-mile oval racetrack. The distance of 6 furlongs was chosen as this is a standard distance for horse racing. The workout differs from a standard race in one significant way. During a 6-furlong race, the horses break from the gate in an extension of the backstretch, race down the backstretch, through the far turn, and down the homestretch to the finish line (see Fig. 3 for track details). In a morning workout, each horse was warmed up by trotting and slow galloping by the rider before the workout. Each individual horse was allowed to slowly approach the 6-furlong pole (Fig. 3). At approximately 50e75 yards before reaching the break off point, the horse was eased over close to
Backstretch
Far turn
Clubhouse turn
Homestretch Figure 3. A schematic drawing of a standard 1-mile racetrack with the sections of the track labelled. The 6-furlong workout observed in this study is indicated by the dashed line.
the inside rail and allowed to reach a full run so as to be at a full run when passing the 6-furlong mark. The portion of the race where stride usage was monitored is indicated by the dashed line in Fig. 3. Because the 6-furlong mark is within the clubhouse turn, the horses started the workout while turning. The horses completed the clubhouse turn, ran down the backstretch, through the far turn, and down the homestretch to the finish line. Each racehorse was tested individually. The total number of strides for the distance was recorded while recording the number of LLSPs and RLSPs used by each individual racehorse. Each individual racehorse was timed. All racehorses tested were stabled at San Luis Rey Downs training centre in Bonsall, California. Racehorses were selected at random from approximately 500 horses stabled at San Luis Rey Downs without regard to abilities or level of training.
Comparison of Right Lead and Left Lead Stride Patterns Five young prospective thoroughbred racehorses stabled at Galway Downs in Temecula, California, were examined. All horses were under the care of the same trainer and were ridden by the same rider. All five horses were tested while running a simulated race at various distances. The track was freshly harrowed before each trial and each horse was tested while performing alone. When a lead change was observed on a straight portion of the track, it was immediately identified on the track surface, and each hoofprint was marked with a small wire flag placed in the anterior point of the hoofprint. At least two full strides before the lead change and at least two strides after the lead change were flagged. A stake was then placed through a 100-yard measuring tape and pulled taut and secured at the opposite end with another stake. The tape connected the innermost (left side) hoofprint in each stride and served as the X axis in a Cartesian coordinate system to localize each hoofprint. A carpenter’s square was used to localize hoofprints at right angles to the measuring tape (along the Y axis). Where the square intersected the tape defined the position along the X axis and the distance perpendicular to the tape defined the Y axis (see Fig. 4). Thus the position of each hoofprint was mapped on a Cartesian coordinate including the stance phases and the suspension phases. The trailing hindlimb of each lead pattern constituted the 0 position along the Y axis and the innermost hoofprint (left side) constituted the 0 position on the X axis. The two stride patterns before the lead change were designated stride no. 1 and stride no. 2. The two stride patterns after the lead change were designated stride no. 3 and stride no. 4, respectively. Stride patterns no. 1 and no. 4 were used for a comparative analysis. These two strides were chosen for comparison because stride no. 2, the last stride pattern before the change, and stride no. 3, the first stride pattern after the change, may be modified by the horse to assist in the lead change. Of the two patterns, the left lead stride pattern was converted to a mirror image for comparison with the right lead stride pattern (Fig. 4). We also compared stride no. 1 with stride
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
(a)
(c)
(b)
Figure 4. Schematic diagram showing the technique for measuring and comparing (a) right lead stride pattern (RLSP) and (b) left lead stride pattern (LLSP) in horses. Location of the hoofprints was marked and their position localized on Cartesian coordinates. (c) A mirror image of the RLSP was generated and superimposed over the LLSP.
no. 2 to see whether the horses modified their stride pattern in preparation for a lead change. RESULTS
Do Racehorses Have a Preferred Lead Stride Pattern?
significantly different from the predicted results for any category (chi-square test: c25 ¼ 0:14; P ¼ 0.99). Thus, the percentage of horses preferring RLSP during the trot-togallop transition did not vary with breed or sex.
Breaking from the starting gate
Trot-to-gallop transition We observed 209 racehorses across genders and breeds to examine differences in lead preferences during the trotto-gallop transition (Table 1). To test for laterality at the population level, we calculated the mean SEproportion of horses that started in their RLSP (0.91 0.004). We used a one-value t test to determine whether this value was significantly different from 0. The difference was highly significant (t test: t5 ¼ 102.8, P 0.01). We also examined whether the numbers of horses preferring their RLSP versus their LLSP differed according to breed or sex (six categories: male thoroughbreds, female thoroughbreds, male Arabians, female Arabians, male American Quarter horses, female American Quarter horses). We conducted separate tests for stride pattern choice during the trot-to-gallop transition and while breaking from the starting gate. Of the 209 horses tested, 190 (90.9%) completed the transition in their RLSP. This ratio was used to calculate the expected number of horses in each category. For example, 35 male thoroughbreds were observed during the trot-to-gallop transition. Of these, we would expect 32 to use their RLSP (90.9% of 35) and three to use their LLSP. The expected numbers were then compared with the observed values. The observed results did not differ
We observed 9116 horses across genders and breeds to examine differences in lead preferences while breaking from the starting gate (Table 2). The table shows the actual numbers as well as the proportion for each of six categories. We again calculated the mean SE proportion of horses that started in their RLSP (0.89 0.008). A onevalue t test showed the mean was significantly different from 0.5 (t test: t5 ¼ 46.5, P 0.01). We also carried out a second chi-square analysis to examine stride pattern preference when breaking from the starting gate. Of the 9116 horses observed, 90.2% (8226 of 9116) broke from the gate in their RLSP. We again used this percentage to calculate predicted numbers of horses in each of the six categories. The resulting P value was small, but not significant (chi-square test: c26 ¼ 10:7; P ¼ 0.057, power ¼ 0.70). Although the probability value was small, we calculated the power (Hintze 2004). Given the high power, we can conclude that any effect of breed or sex was slight. The decreased probability was principally due to the results from the female Arabians, probably because of the small sample size in this category. An additional 85 thoroughbred horses were observed breaking from the starting gate on racetracks in Hong Kong and Australia. Of the 85 observed, 92% preferred their RLSP and 8% preferred their LLSP. This is relevant
Table 1. Stride pattern preference during the trot-to-gallop transition Thoroughbreds
RLSP LLSP
Arabians
American Quarter horses
Male
Female
Male
Female
Male
Female
32 (0.91) 3 (0.09)
38 (0.90) 4 (0.10)
13 (0.93) 1 (0.07)
22 (0.92) 2 (0.08)
46 (0.90) 5 (0.10)
39 (0.91) 4 (0.09)
Results are shown as total numbers and proportions (in parentheses) of horses observed.
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ANIMAL BEHAVIOUR, 74, 4
Table 2. Stride pattern preference while breaking from the starting gate Thoroughbreds
RLSP LLSP
Arabians
American Quarter horses
Male
Female
Male
Female
Male
Female
2943 (0.91) 306 (0.09)
2791 (0.91) 273 (0.09)
70 (0.90) 8 (0.10)
41 (0.85) 7 (0.15)
1246 (0.88) 165 (0.12)
1135 (0.90) 131 (0.10)
Results are shown as total numbers and proportions (in parentheses) of horses observed.
because in Hong Kong and Australia, horses race clockwise around the track as compared to anticlockwise in U.S.A.
87.67.6. These two means were not significantly different (Mann-Whitney U test: U ¼ 67.5, N1 ¼ 27, N2 ¼ 5, P ¼ 0.69).
Multiple observations from individual racehorses A total of 32 thoroughbred racehorses, including 17 females and 15 males, were used for repeated observations breaking from the starting gate for five to seven races (Table 3). Individual racehorses are typically rested for 30 days between races, limiting the number of observations. Of the horses tested, 62.5% started every race in the same stride pattern (20/32), 31% started one race in their nonpreferred stride pattern (10/32) and 6% started two races in their nonpreferred stride pattern (2/32). When combining the preferences from all racehorses, an individual racehorse had a 94% probability that it would use its preferred stride pattern. To test for laterality on the individual level, we calculated a laterality index (LI) for each horse (Fig. 5). We first tested for laterality in general without regard to side preference by using the absolute value of LI. The mean LI value was 87.23.2. This value was significantly different from 0 (t test: t31 ¼ 27.4, P 0.01). During the repeated observation studies, horses would occasionally break from the gate in their nonpreferred stride. The mean LI for horses that preferred their RLSP most of the time was 87.1 3.6 and the mean LI for horses that preferred their LLSP most of the time was Table 3. Multiple observations from individual horses of left (L) and right (R) stride pattern preference when starting from the gate
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Females
Males
LRRRRRR RRRRRR RRRRRRR RLLLLL RRRRR RLRRRRL LLLLLLL RRRRR RRRRRRR RRRRRR RRRRRRL RRRRRR RRRRRRR LLLLLLL RRRRR RRRRRRR RRLRRRR
RRRRR RRLRRLR RRRRRR RRRRRRR RRRLRRR LLLLLLL RRRRR RRRRRR RRLRRR RRRRRRL RLRRRRR RRRRRR RRRRRRR RLLLLLL RRRLRRR
Does Stride Pattern Preference Effect How a Horse Runs in a 6-Furlong Morning Workout? We examined whether the clear stride pattern preference when first breaking into a gallop influenced the stride pattern selection during a race. Because of the difficulty in monitoring strides and stride changes during an actual race, strides were counted, and lead changes noted for 12 thoroughbreds during a 6-furlong morning workout simulating a race (see Fig. 2). The number of strides and lead changes across time for each horse are shown in Table 4. Since the 6-furlong workout begins within the clubhouse turn, all the horses began the workout in their LLSP. Upon reaching the backstretch, 11 of the 12 horses switched to the RLSP and one (horse 5) remained in the LLSP. This is approximately the percentage we would expect from the previous stride pattern preference study. None of the horses switched stride during the backstretch. Upon reaching the far turn, all the horses again switched to the LLSP, which they maintained throughout the far turn. After entering the homestretch, all 12 horses switched to their RLSP. Eight of the horses maintained their RLSP for the duration of the workout. Two horses switched back into their LLSP during the homestretch, including horse 5, which had run most of the race in its LLSP. The final two horses changed lead 20 15 Horses
946
10 5 0
–100 –80 –60 –40 –20
0
20
40
60
80 100
Laterality index Figure 5. The frequency distribution of the laterality index (LI) for the right lead stride pattern (RLSP) preference in 32 horses. The distribution was bimodal, showing the pervasiveness of laterality in galloping racehorses. The mean LI for left preferred horses and right preferred horses was not significantly different.
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
Table 4. Stride pattern selection of 12 racehorses during a 6-furlong morning workout Horse 1 2 3 4 5 6 7 8 9 10 11 12
Clubhouse turn 1e5L 1e8L 1e6L 1e11L 1e3L 1e4L 1e6L 1e4L 1e3L 1e8L 1e15L
Backstretch 6e95R 9e91R 7e81R 12e90R 1e118L 4e85R 5e84R 7e93R 5e86R 4e89R 9e94R 16e84R
Far turn
Homestretch
Time (s)
96e125L 92e121L 82e120L 91e120L
126e184R 122e166R, 167e183L 121e173R 121e177R 119e141R, 142e180L 120e179R 124e135R, 136e161L, 162e185R 123e188R 121e155R, 156e164L, 165e182R 122e186R 124e183R 132e181R
115 113.2 112.3 113.4 114.1 115.1 116 113 114.3 112.4 113.3 114.2
86e119L 85e123L 94e122L 87e120L 90e121L 95e123L 85e131L
stride twice during the homestretch, from RLSP to LLSP and back to RLSP.
25
Comparison of Right Lead and Left Lead Stride Patterns in Racehorses 20
15
Length (ft)
Five horses were run anticlockwise for one-fourth to five-eighths of a mile on a standard racetrack. Each horse was observed using the left lead stride pattern while negotiating the turn. As each horse straightened out for the stretch run, they ran a few strides in the left lead stride pattern and then switched to the right lead stride pattern. Because all five horses switched to their RLSP as soon as possible, all five appeared to prefer their RLSP. The point of lead change was noted and strides immediately before and after the stride change were individually mapped according to phase (suspension or stance) on a Cartesian coordinate system. At least two strides per phase were mapped. Stride no. 1 and stride no. 2 were LLSPs immediately before a lead change. Stride no. 3 and stride no. 4 were RLSPs immediately following the lead change. A mirror image of stride no. 1 (LLSP) was produced and superimposed onto stride no. 4 (RLSP) so that hoof no. 1 (the trailing hindhoof) during strides 1 and 4 overlapped (Fig. 6). Although there was variation from horse to horse, the RLSP (triangles) and LLSP (squares) were clearly not mirror images of one another. In general, the stance phase of the LLSP appeared to be longer. To examine this more closely, we graphed the duration of the stance phase, suspension phase and total stride for the five horses (Fig. 7). There was no significant difference between the RLSP and the LLSP for stance length (paired t test: t4 ¼ 1.83, P ¼ 0.14), suspension phase length (t4 ¼ 1.25, P ¼ 0.28) or total stride length (t4 ¼ 1.21, P ¼ 0.29). Although there was not a significant difference between the lengths of the different components of the RLSP and the LLSP, in four of the five horses tested, the stance phase of the LLSP was longer than that of the RLSP, while the suspension phase of the LLSP was shorter than that of the RLSP. In two of the horses, the total length of the LLSP was shorter than that of the RLSP, whereas in the other three horses, the total length of the LLSP was longer. Finally, to examine whether the length of the stride immediately before and after a switch differed, we compared
10
5
0
–2
0
2
Width (ft) Figure 6. Comparison of the right lead stride pattern (:: RLSP) and the mirror image of left lead stride pattern (-: LLSP) in five thoroughbred racehorses. Positions of the hoofprints on the track were recorded, the LLSP was converted to a mirror image and the two stride patterns superimposed. The first hind footprints were superimposed.
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ANIMAL BEHAVIOUR, 74, 4
25
Distance (ft)
20
LLSP stance RLSP stance LLSP air RLSP air LLSP total
15 10
RLSP total
5 0
1
2
3
4
5
Horse no. Figure 7. Comparison of left (LLSP) and right lead stride pattern (RLSP) length in thoroughbred racehorses during the stance and suspension (air) phases and of total stride length for each stride pattern.
stride no. 1 (LLSP) with stride no. 2 (Fig. 8). When performing a stride switch, the horse changes stride during the suspension phase. The stance phase comparison for the normal and switch stride was not significantly different (paired t test: t4 ¼ 0.98, P ¼ 0.38), however, a significant increase was seen in both the suspension phase (t4 ¼ 7.18, P ¼ 0.002) and the total stride length (t4 ¼ 9.80, P ¼ 0.001). This result suggests that a racehorse ‘pushes off’ more strongly during the stance phase immediately preceding the switch in the suspension phase.
DISCUSSION The results from the first study clearly show that racehorses have a preference for which stride pattern to use when breaking from the standing position in the starting gate, or making the trot-to-gallop transition. Consistently across sexes and breeds, 90% of all horses observed preferred their right lead stride pattern while 10% preferred their left lead stride pattern. In addition, the results from the repeated measures test revealed that most individual racehorses preferred the same lead stride pattern most of the time. Although all the horses showed a distinct preference in the repeated measures test, occasionally a horse would start in its nonpreferred lead. This result 30
**
25 Length (ft)
948
20 15
**
10 5 0
Stance
Suspension
Total
Figure 8. Comparison of normal left lead stride patterns, LLSPs (,) , and LLSPs associated with a switch (-; horses switch stride pattern during the suspension phase). Values are means SE, N ¼ 5, paired t test: *P < 0.05.
might also be attributed to the jockey or the assistant starter holding the horse’s head to one side before breaking, thus physically influencing the horse. There is only one previous study that examined stride pattern preference in galloping horses. Deuel & Lawrence (1987) suggested that galloping horses have a preference for their LLSP. In their study, four American Quarter horses were tested while running down a 115-m straight track, and all preferred the left lead. These results appear to contrast with those of our study. It is possible that their experimental conditions influenced the choice of stride pattern, because the horses’ running was constrained to permit video monitoring. The horses’ stride pattern choice may also have been influenced by the people and equipment involved in recording the horses. Finally, it is also possible that randomly picked four horses that preferred their LLSP. Our results also appear to contrast with those of previous laterality studies in horses (McGreevy & Rogers 2005; Murphy et al. 2005; Larose et al. 2006). In these studies, laterality was sometimes seen at the individual level, but only weakly, or not at all, at the population level. Murphy et al. (2005) also showed that laterality was correlated with sex in horses. Our current study showed a strong laterality at both the individual and population levels. Furthermore, laterality did not differ between breeds and sexes. Such pervasive laterality (90% versus 10%) has only been seen in handedness in humans (reviewed in Warren 1980) and footedness in some species of parrots (reviewed in Harris 1989; Rogers 1996). Even in parrots, only certain species show a strong preference for holding food in their left foot while eating. Other species showed no preference and a few species are right-footed. It is important to stress at this point that stride pattern preference in racehorses is not a result of training. At no time during their training are racehorses ‘trained’ in a particular stride pattern. They are not ‘trained’ to leave the starting gate in a specific ‘lead’ nor are they trained to change ‘leads’ for turn negotiation, although some riders will try to force a change in stride lead patterns by shifting their weight, pulling the horse’s head to one side using the reins, or whipping the horse’ (on the shoulder, belly, or behind). At slower speeds (during training), many horses
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
will gallop around the turn in their right lead. Horses may learn to change leads for the turn, but they do not all change at the same location before the turn, nor do they all switch back at the same location after leaving the turn. Thus, horses change leads in the turn not because they are trained to do so but because they need to negotiate the turn at fast or full runs. This assertion is reinforced by the results observed in American Quarter horses and thoroughbreds raced in Australia and Hong Kong. American Quarter horses are almost exclusively trained on straight tracks and most run their races in one lead stride pattern. The thoroughbreds in Australia and Hong Kong are trained and race clockwise around the racetrack. In spite of this, both of these groups showed a stride pattern preference that was not significantly different from that of thoroughbreds and Arabians on American tracks. Although horses are not consciously trained to run in a particular stride pattern, there may be an unconscious influence. Riders and other handlers of horses typically approach horses always from the left side. It is possible that this behaviour might in turn influence the horse (Grzimek 1968). It is unclear whether trainers’/riders’ propensity to approach horses from the left developed from a peculiarity of the horse (they are less ‘spooked’ when approached from the left) or the humans riding the horse (usually right-handed). Larose et al. (2006) studied laterality in two breeds of horse: French Saddlebreds and Trotters. The French Saddlebreds are saddle-ridden horses and as such are traditionally approached from the left. The Trotters are harness racers and are typically approached from either side. The two breeds show exactly the same trends in laterality. Murphy et al. (2005) also found a difference in laterality based on sex. These two studies suggest that laterality is not determined solely by humans’ handling of horses in a lateralized manner. Although the horses observed in our study were not specifically trained to race in a particular stride pattern, they were intensively trained to race. The strong laterality observed in our study, but not seen in previous studies, might be a consequence of training. An untrained horse might be more likely to begin running in its nonpreferred stride than a highly trained horse. Counting of stride and lead changes during a morning workout revealed that stride pattern preference influences stride pattern usage during a race. Although racehorses are mechanically constrained to negotiate turns in their LLSP, they are free to choose either stride pattern during the straight stretches. Our results suggest that racehorses change lead stride patterns between two and four times during a 6-furlong race. These numbers are in contrast to Deuel & Lawrence (1987), who suggested that racehorses run the full race using one stride pattern. In addition, the number of lead changes observed in our study contrast strongly with those of a previously published report, which claimed that some horses may change lead stride pattern over 30 times during a race and that other horses run the entire race in the same lead pattern (Leach 1987). While running a simulated race, racehorses will spend most of their time in their preferred lead unless compelled to do otherwise (while in the turn). This was particularly apparent in horse 5, which ran almost the entire race in its LLSP. Only
at the end of the race, perhaps as the horse was tiring, did it switch stride patterns. None of the 12 horses tested ran the entire distance without switching lead stride pattern. Variation in stride pattern usage was consistent but not significantly different in five of the horses we examined. This result may prove significant with a larger sample size. A small difference in stride patterns could compound into a major effect over the course of a race. For example, should a horse have a difference of only one-eighth of an inch between the RLSP and the LLSP, going a mile using 235 strides there would be a difference of approximately 30 inches; many races are decided by only inches. Deuel & Lawrence (1987) suggested that horses running in either their RLSP or LLSP do not change the frequency of their strides, but do change the length. Thus, an increase in stride length will result in an increase in speed. Also, the stance phase is shortened and the suspension phase is lengthened during the stride change. This finding suggests that the stride change requires a special effort, and thus, that the number of stride changes during a race should be minimized for optimal performance. The domestic horse, Equus caballus, is likely to be an ideal candidate to study laterality at the population level. The horse has laterally positioned eyes with little overlap to support bilateral vision (Brooks et al. 1999; Larose et al. 2006). Previous work has suggested that animals with laterally placed eyes use them in an asymmetrical way (Evans et al. 1993; Lippolis et al. 2002, 2005; Larose et al. 2006). Vallortigara & Rogers (2005) suggested that, across many species, the left hemisphere (and the associated right sensory structures) is more involved with analytical analysis of stimuli, while the right hemisphere (and left sensory structures) is more directed towards emotional evaluations. Furthermore, horses are herd animals. It has been suggested that laterality in social animals might play a role in maintaining group integrity (Rogers 2002). Bisazza et al. (2000) examined 16 species of fish and looked for laterality in the tendency to turn in a particular direction when confronted with a predator. Of the six species that were gregarious, 100% showed a population-level laterality. Of the 10 nongregarious species, 60% showed a population-level laterality. Note, however, that the four species that were not lateralized at the population level still displayed laterality at the individual level. Finally, laterality when running in racehorses might have a biomechanical component. As stated earlier, there is a direct link between breath and stride, with exactly one breath/stride. If left and right stride patterns do not match (Deuel & Lawrence 1987; Drevemo et al. 1987), the amount of oxygen exchanged during the LLSP and the RLSP might also differ. The lungs of horses are asymmetrical, with the right, lung having an additional lobe (Getty 1975) so running in the RLSP might allow increased expansion of the right side of the chest cavity and increased oxygen exchange in the right lung. Even if the amount of oxygen exchanged during both stride patterns is the same (i.e. maximal), there still might be differences in the efficiency of the strides, causing more oxygen to be consumed in one stride pattern compared to the other. Although the 90:10 laterality ratio suggests that laterality is a primary cause for stride pattern preference, this does
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not preclude the possibility that consistently running in a preferred stride pattern could result in a biomechanical benefit. Given that individual racehorses prefer a particular stride pattern and that there is a correlation between stride length and breathing in racehorses, as well as constraints on stride pattern for particular parts of the racetrack (LLSP in turns, either RLSP or LLSP in straightaway), stride pattern preference might allow a horse to use the optimum sequence of stride patterns during the course of a particular race. If this is the case, stride pattern preference might not only affect performance, it might dictate performance as well. References Adams, O. R. 1979. Lameness in Horses. 3rd edn. Philadelphia: Lea & Febiger Publishing. Ades, C. & Ramires, E. N. 2002. Asymmetry of leg use during prey handling in the spider Scytodes globula (Scytodidae). Journal of Insect Behavior, 15, 563e570. Bisazza, A., Pignatti, R. & Vallortigara, G. 1997. Laterality in detour behavior: interspecific variation in poeciliid fish. Animal Behaviour, 54, 1273e1281. Bisazza, A., Cantalupo, C., Capocchiano, M. & Vallortigara, G. 2000. Population lateralization and social behavior: a study with 16 species of fish. Laterality, 5, 269e284. Brooks, D. E., Komaromy, A. M. & Kallberg, M. E. 1999. Comparative retinal ganglion cell and optic nerve morphology. Veterinary Ophthalmology, 2, 3e11. Budiansky, S. 1997. The Nature of Horses. New York: Free Press. Byrne, R. A., Kuba, M. J. & Meisel, D. V. 2004. Lateralized eye use in Octopus vulgaris shows antisymmetrical distribution. Animal Behaviour, 68, 1107e1114. Casey, M. B. 2005. Asymmetrical hatching behaviors: the development of postnatal motor laterality in the three precocial bird species. Developmental Psychobiology, 47, 123e135. Cowell, P. E., Waters, N. S. & Denenberg, V. H. 1997. Effects of early environment on the development of functional laterality in Morris maze performance. Laterality, 2, 221e232. Deuel, N. R. & Lawrence, L. M. 1987. Laterality in the gallop gait of horses. Journal of Biomechanics, 20, 645e649. Drevemo, S., Fredricson, I. & Hjerte´n, G. 1987. Early development of gait asymmetries in trotting Standardbred colts. Equine Veterinary Journal, 19, 189e191. Evans, C. S., Evans, L. & Marler, P. 1993. On the meaning of alarm calls: functional references in an avian vocal system. Animal Behaviour, 46, 23e28. Getty, R. G. 1975. Sisson and Grossman’s The Anatomy of the Domestic Animals. 5th edn. Philadelphia: W. B. Saunders. Glick, S. D. & Ross, D. A. 1981. Right-sided population bias and lateralization of activity in normal rats. Brain Research, 205, 222e225. Grzimek, B. 1968. On the psychology of the horse. In: Man and Animal: Studies in Behavior (Ed. by H. Friedrich), pp. 37e45. New York: St. Martin’s Press. Harris, L. J. 1989. Footedness in parrots: three centuries of research, theory, and mere surmise. Canadian Journal of Psychology, 43, 369e396. Hews, D. K., Castellano, M. & Hara, E. 2004. Aggression in females is also lateralized: left-eye bias during aggressive
courtship rejection in lizards. Animal Behaviour, 68, 1201e 1207. Hildebrand, M. 1977. Analysis of asymmetrical gaits. Journal of Mammalogy, 58, 131e156. Hintze, J. 2004. NCSS and PASS. Kaysville, Utah: Number Cruncher Statistical Systems. Hoyt, D. F. & Taylor, C. R. 1981. Gait and the energetics of locomotion in horses. Nature, 292, 239e240. Larose, C., Richard-Yris, M.-A., Hausberger, M. & Rogers, L. 2006. Laterality of horses associated with emotionality in novel situations. Laterality, 11, 355e367. Leach, D. H. 1987. Locomotion of the athletic horse. In: Equine Exercise Physiology. Vol. 2 (Ed. by J. R. Gillespie & N. E. Robinson), Davis, California: ICEEP Publications. Lippolis, G., Bisazza, A., Rogers, L. & Vallortigara, G. 2002. Lateralisation of predator avoidance responses in three species of toad. Laterality, 7, 163e183. Lippolis, G., Westman, W., McAllan, B. M. & Rogers, L. J. 2005. Lateralisation of escape responses in the striped-faced dunnart Sminthopsis macroura (Dasyuridae: Marsupialia). Laterality, 10, 457e470. McGreevy, P. D. & Rogers, L. J. 2005. Motor and sensory laterality in thoroughbred horses. Applied Animal Behaviour Science, 92, 337e352. Murphy, J., Sutherland, A. & Arkins, S. 2005. Idiosyncratic motor laterality in the horse. Applied Animal Behaviour Science, 91, 297e310. Muybridge, E. 1899. Animals in Motion. London: Chapman & Hall. Robins, A. & Rogers, L. J. 2004. Lateralized prey-catching responses in the cane toad, Bufo marinus: analysis of complex visual stimuli. Animal Behaviour, 68, 767e775. Rogers, L. J. 1996. Behavioral, structural and neurochemical asymmetries in the avian brain: a model system for studying visual development and processing. Neuroscience and Biobehavioral Reviews, 20, 487e503. Rogers, L. J. 2002. Advantages and disadvantages of lateralization. In: Comparative Vertebrate Lateralisation (Ed. by L. J. Rogers & R. J. Andrew), pp. 126e153. Cambridge, U.K.: Cambridge University Press. Rogers, L. J. & Andrew, R. J. 2002. Comparative Vertebrate Lateralization. Cambridge, U.K.: Cambridge University Press. Roth, E. D. 2003. ‘Handedness’ in snakes? Lateralization of coiling behaviour in a cottonmouth, Agkistrodon piscivorus leucostoma, population. Animal Behaviour, 66, 337e341. Schwarting, R. K. & Borta, A. 2005. Analysis of behavioral asymmetries in the elevated plus-maze and in the T-maze. Journal of Neuroscience Methods, 141, 251e260. Vallortigara, G. & Bisazza, A. 2002. How ancient is brain lateralization? In: Comparative Vertebrate Lateralisation (Ed. by L. J. Rogers & R. J. Andrew), pp. 9e69. Cambridge, U.K.: Cambridge University Press. Vallortigara, G. & Rogers, L. J. 2005. Survival with an asymmetrical brain: advantages and disadvantages of cerebral lateralization. Behavioral and Brain Sciences, 28, 575e633. Ventolini, N., Ferrero, E. A., Sponza, S., Chiesa, A. D., Zucca, P. & Vallortigara, G. 2005. Laterality in the wild: preferential hemifield use during predatory and sexual behaviour in the black-winged stilt. Animal Behaviour, 69, 1077e1084. Warren, J. M. 1980. Handedness and laterality in humans and other animals. Physiological Psychology, 8, 351e359. Wells, D. L. 2003. Lateralised behaviour in the domestic dog, Canis familiaris. Behavioural Processes, 61, 27e35.
Laterality in stride pattern preferences in racehorses D. E. WILLIAMS* & B . J. NOR RIS †
*Department of Forest, Rangeland, and Watershed Stewardship, Warner College of Natural Resources, 120 Forestry Bldg, Colorado State University, Fort Collins, U.S.A. yDepartment of Biological Sciences, California State University, San Marcos (Received 14 July 2006; initial acceptance 18 August 2006; final acceptance 15 January 2007; published online 19 September 2007; MS. number: A10512R)
During performance, racehorses gallop in an asymmetrical stride with either the left hindhoof striking the ground first (right lead stride pattern) or the right hindhoof striking the ground first (left lead stride pattern). In this study we examined racehorses for a stride pattern preference. Here, we showed that racehorses do have a preference for one stride pattern over the other. Across thoroughbreds, Arabians, and American Quarter horses 90% preferred their right lead stride pattern with 10% preferring the left. In a repeated studies test, a single racehorse consistently preferred one stride pattern over the other. We further showed that stride pattern preference is reflected in stride pattern usage during a 6-furlong morning workout. Horses will run in their preferred stride pattern unless forced to switch while turning, injured, or fatigued (at the end of the race). Finally, we showed that in a small sample, there were minor variations between the right and left lead stride patterns. Because running is intimately linked to respiration in performing racehorses, stride pattern preference might contribute to performance in racehorses. Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Keywords: Equus caballus; laterality; racehorse; stride
Until recently, laterality or handedness, a preferential usage of one side of the body was studied almost exclusively in humans. In more recent years, laterality has been shown to be a widespread phenomenon in a number of vertebrate species (for recent reviews see Bisazza et al. 1997; Rogers & Andrew 2002). Laterality at either the individual or population level has been observed across a wide range of vertebrates including fish (Bisazza et al. 1997, 2000), amphibians (Robins & Rogers 2004), reptiles (Roth 2003; Hews et al. 2004), birds (Casey 2005; Ventolini et al. 2005) and mammals other than primates (Glick & Ross 1981; Cowell et al. 1997; Wells 2003; Schwarting & Borta 2005). It has even been observed in invertebrates (Ades & Ramires 2002; Byrne et al. 2004). These results and others suggest that lateralization is a phenomenon that probably arose early in vertebrate evolution (Vallortigara & Bisazza 2002). In this study we wanted to look for laterality in the racehorse (Equus caballus). Laterality in racehorses is of particular importance because several authors have Correspondence and present address: B. J. Norris, Department of Biological Sciences, CSUSM, San Marcos, CA 92096, U.S.A. (email: [email protected]). D. E. Williams is now at the 222 East View Street, Fallbrook, CA 92028, U.S.A. 0003e 3472/07/$30.00/0
suggested that a laterality bias might affect performance (McGreevy & Rogers 2005; Larose et al. 2006). When a horse is running, it tends to use a stride pattern known as the asymmetrical transverse gallop gait (Hildebrand 1977; Budiansky 1997). This gait consists of two phases: (1) the stance phase when one or more of the horse’s hooves are on the ground; and (2) the suspension phase when the horse is completely airborne (Muybridge 1899). The stance phase is asymmetrical (Adams 1979) with either the right forehoof (right lead stride pattern, RLSP) or the left forehoof (left lead stride pattern, LLSP) touching the ground last (Fig. 1). In the tracks on the ground, the hoof to touch last is in the ‘Lead’. There are distinct differences between the functions of the left and right hooves during asymmetrical gallop gait (Deuel & Lawrence 1987; Drevemo et al. 1987). If the left side and the right side are used slightly differently during the gallop, then laterality might enhance performance if a horse can perform in its preferred stride pattern. When a horse is running, there is a direct link between breathing and galloping with exactly one breath/stride (Hoyt & Taylor 1981). Because of biomechanical constraints, the horse exhales while in the stance phase and inhales while in the suspension phase. Given the direct link between stride pattern and breathing, the possibility exists that
941 Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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(a)
(b)
LR(1)
LF(3)
RR(2)
LF(4)
LR(2)
RF(4)
RR(1)
RF(3)
Figure 1. Photographs of racehorses in their (a) right lead stride pattern (RLSP) and (b) left lead stride pattern (LLSP). The stride patterns are named for the hoofprints left on the ground, which are shown schematically below each horse. Numbers in parentheses indicate the sequence in which the hooves contact the ground.
a preference for one stride pattern over the other may be linked to performance. Any or all of these factors might combine to give racehorses a preference when running in the asymmetrical gallop. If racehorses display laterality, then running efficiency might vary with lead stride pattern. Recently, there have been several important studies examining laterality in the domestic horse. Deuel & Lawrence (1987) used high-speed cinematography to examine the gallop in American Quarter horses. Although their study involved only four horses, they were able to show that these horses displayed a preference for galloping in their left lead. They were also able to document differences between the left lead and right lead stride patterns. Murphy et al. (2005) also observed laterality in the motor activities of horses. They observed whether horses preferred initiating movement from a standing start with their right leg or left leg. They further observed whether horses preferred passing an obstacle on their left or right under different circumstances. Across all horses tested, there was significant lateralization in that most horses consistently preferred either their right or left side. However, the numbers that preferred the right were not significantly different from the numbers that preferred the left. These results suggest that for the properties measured, horses display laterality at the individual level, but not at the population level. However, when they compared the results based on sex, a significant populationlevel difference was observed in that females displayed significantly more right lateralized responses while males were significantly more left lateralized. McGreevy & Rogers (2005) looked at both motor and sensory laterality in thoroughbreds. When observing whether horses stood with their right limb or left limb advanced, they observed that amongst horses that had a preference, more horses
preferred their left limb. They also observed that preference was stronger in older horses. When the population as a whole was compared, there was a significant left advanced preference. They also examined nostril preference when investigating an interesting olfactory stimulus (stallion faeces). Younger horses showed a significant right nostril bias, but older horses showed no bias. Interestingly, there was no correlation in motor and sensory bias in horses that were tested for both. Finally, Larose et al. (2006) tested whether two breeds of horses preferred to examine a novel stimulus with their right or left eye as well as their right or left nostril. Although there was no significant laterality observed across all horses, there was a correlation between the emotionality of the novel stimulus (as indicated by the horses’ behaviour) and a tendency to view the novel stimulus with the left eye. Taken together, these studies indicate that while horses may show laterality at the individual level, there is little evidence for laterality at the population level. When breaking into a run from a standing start or when transitioning from a trot to a gallop, a racehorse must decide which lead stride pattern to use. Although racehorses are constrained to using their inside lead around turns (LLSP when running anticlockwise around a track; Adams 1979), they have a choice as to which lead to use on straight sections of the track. In this study, we hypothesized that racehorses have a preference for either their right or left lead stride pattern. We tested this by observing racehorses as they began running from a standing start (breaking from the starting gate) and while making the trot-to-gallop transition. We made repeated observations to test stride pattern preference consistency within individual racehorses. We also monitored stride selection during a 6-furlong run. Finally, we compared LLSP and RLSP within individual horses to look for consistent variation
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
between the two stride patterns. If racehorses have a preferred stride pattern, it might in turn influence a horse’s ability to run races at various distances (i.e. sprints that are normally run around one turn, distance races running around two turns; the full track).
METHODS
Animals A total of 9362 horses were observed during the course of the study. Animals observed included thoroughbreds, Arabians, and American Quarter horses. All animals were observed in the U.S.A., where horses race around an oval racetrack in an anticlockwise direction. Because training to race in a particular direction might influence stride pattern preference, American Quarter horses, which race in a straight line, serve as an internal control. The horses were not experimentally manipulated in any way. Observations were made on horses during normal training sessions and while breaking from the gate during races.
Lead Stride Pattern Preference Trot-to-gallop transition During warm-up for morning training sessions, 209 racehorses were observed making the trot-to-gallop transition, and the gender and lead stride pattern of the transverse gallop gait was observed and recorded. If the horse’s left front limb was in the lead position during the first gallop stride from the trot-to-gallop transition, and continued in the same lead, the horse was recorded as using the left lead stride pattern (LLSP). All thoroughbreds were observed at San Luis Rey Downs Training Center in Bonsall, California. All American Quarter horses and Arabian racehorses were observed at Los Alamitos Race Course in Cypress, California. All observations were carried out during one morning training session to rule out the possibility of recording the same horse twice. Only transitions occurring on straight sections of the track were recorded to rule out the possibility of stride pattern preference for turn negotiation benefit.
Breaking from the starting gate When performing, a racehorse starts the race from the standing position in the starting gate. When the horse was observed to break from the starting gate leading with the left forelimb, the horse was recorded as using a left lead stride pattern (Fig. 2). A total of 9116 horses were observed. Video replay examinations were used from Los Alamitos Race Course, in Cypress, California, for the American Quarter horse and the Arabian racehorses. Video replay examinations for the thoroughbred racehorses were used from Del Mar, Hollywood Park, and Santa Anita racetracks in southern California. An additional 85 horses were observed breaking from the starting gate in racetracks in Hong Kong and Australia. These horses race clockwise around the racetrack (as opposed to anticlockwise in U.S.A.) and serve as a further control that stride pattern preferences are not ‘trained’.
Multiple observations from individual racehorses To test whether racehorses consistently express a stride pattern preference, we carried out multiple observations of particular racehorses. We examined video replays of thoroughbred racehorses that were stabled at San Luis Rey Downs Training Center in Bonsall, California and participated in races at southern California racetracks. Stride patterns of 32 horses were recorded during five to seven races for a repeated studies examination.
Statistical Analysis We tested for laterality at the population level for both the trot-to-gallop transition and while breaking from the starting gate. To do this, we calculated a mean proportion of RLSP: RLSP/(RLSP þ LLSP) from each of the six different categories (thoroughbred males, thoroughbred females, Arabian males, Arabian females, American Quarter horse males, American Quarter horse females). Because the categories did not contain equal numbers of observations, we converted the number of observations to proportions for analysis. We used a one-value t test to determine whether the proportion of RLSP horses was significantly different from 0.5 (RLSP ¼ LLSP).
Figure 2. Photograph of nine horses breaking from the starting gate. Eight of the nine horses are in their right lead stride pattern (RLSP) and one is in the left lead stride pattern (LLSP). Note particularly the no. 9 horse in its RLSP and the no. 2 horse in its LLSP.
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To test for differences based on breed or sex for both the trot-to-gallop transition and breaking from the starting gate, a standard chi-square analysis was used. The percentage of all horses starting in their RLSP for all observations was calculated. This total percentage was used to calculate the expected number of RLSP horses in each of the six categories. The chi-square analysis was used to test whether the observed deviated from the expected in each category. To test for laterality at the individual level, we calculated a laterality index (LI) for each of the 32 horses used in the repeated measures study. The LI was calculated as (RLSP LLSP)/(RLSP þ LLSP)100. If the number of starts in the RLSP is equal to the number of starts in the LLSP, the LI will equal 0. To test for laterality without regard to side, we calculated the mean and standard error for the absolute value of LI for all 32 horses. We then used a one-value t test to determine whether that mean was significantly different from 0. We also examined whether left-lead preferring horses were as likely to start a race in their preferred lead as right-lead preferring horses were. To do this, we calculated the mean of the absolute value of LI for horses that started primarily in their left lead and for horses that started primarily in their right lead. The two means were compared using a ManneWhitney U test.
Stride Pattern Selection during a 6-Furlong Morning Workout Because of the difficulty in counting strides and stride changes of an individual horse during an actual race, 12 thoroughbred racehorses were tested during the course of a 6-furlong morning workout on a standard 1-mile oval racetrack. The distance of 6 furlongs was chosen as this is a standard distance for horse racing. The workout differs from a standard race in one significant way. During a 6-furlong race, the horses break from the gate in an extension of the backstretch, race down the backstretch, through the far turn, and down the homestretch to the finish line (see Fig. 3 for track details). In a morning workout, each horse was warmed up by trotting and slow galloping by the rider before the workout. Each individual horse was allowed to slowly approach the 6-furlong pole (Fig. 3). At approximately 50e75 yards before reaching the break off point, the horse was eased over close to
Backstretch
Far turn
Clubhouse turn
Homestretch Figure 3. A schematic drawing of a standard 1-mile racetrack with the sections of the track labelled. The 6-furlong workout observed in this study is indicated by the dashed line.
the inside rail and allowed to reach a full run so as to be at a full run when passing the 6-furlong mark. The portion of the race where stride usage was monitored is indicated by the dashed line in Fig. 3. Because the 6-furlong mark is within the clubhouse turn, the horses started the workout while turning. The horses completed the clubhouse turn, ran down the backstretch, through the far turn, and down the homestretch to the finish line. Each racehorse was tested individually. The total number of strides for the distance was recorded while recording the number of LLSPs and RLSPs used by each individual racehorse. Each individual racehorse was timed. All racehorses tested were stabled at San Luis Rey Downs training centre in Bonsall, California. Racehorses were selected at random from approximately 500 horses stabled at San Luis Rey Downs without regard to abilities or level of training.
Comparison of Right Lead and Left Lead Stride Patterns Five young prospective thoroughbred racehorses stabled at Galway Downs in Temecula, California, were examined. All horses were under the care of the same trainer and were ridden by the same rider. All five horses were tested while running a simulated race at various distances. The track was freshly harrowed before each trial and each horse was tested while performing alone. When a lead change was observed on a straight portion of the track, it was immediately identified on the track surface, and each hoofprint was marked with a small wire flag placed in the anterior point of the hoofprint. At least two full strides before the lead change and at least two strides after the lead change were flagged. A stake was then placed through a 100-yard measuring tape and pulled taut and secured at the opposite end with another stake. The tape connected the innermost (left side) hoofprint in each stride and served as the X axis in a Cartesian coordinate system to localize each hoofprint. A carpenter’s square was used to localize hoofprints at right angles to the measuring tape (along the Y axis). Where the square intersected the tape defined the position along the X axis and the distance perpendicular to the tape defined the Y axis (see Fig. 4). Thus the position of each hoofprint was mapped on a Cartesian coordinate including the stance phases and the suspension phases. The trailing hindlimb of each lead pattern constituted the 0 position along the Y axis and the innermost hoofprint (left side) constituted the 0 position on the X axis. The two stride patterns before the lead change were designated stride no. 1 and stride no. 2. The two stride patterns after the lead change were designated stride no. 3 and stride no. 4, respectively. Stride patterns no. 1 and no. 4 were used for a comparative analysis. These two strides were chosen for comparison because stride no. 2, the last stride pattern before the change, and stride no. 3, the first stride pattern after the change, may be modified by the horse to assist in the lead change. Of the two patterns, the left lead stride pattern was converted to a mirror image for comparison with the right lead stride pattern (Fig. 4). We also compared stride no. 1 with stride
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
(a)
(c)
(b)
Figure 4. Schematic diagram showing the technique for measuring and comparing (a) right lead stride pattern (RLSP) and (b) left lead stride pattern (LLSP) in horses. Location of the hoofprints was marked and their position localized on Cartesian coordinates. (c) A mirror image of the RLSP was generated and superimposed over the LLSP.
no. 2 to see whether the horses modified their stride pattern in preparation for a lead change. RESULTS
Do Racehorses Have a Preferred Lead Stride Pattern?
significantly different from the predicted results for any category (chi-square test: c25 ¼ 0:14; P ¼ 0.99). Thus, the percentage of horses preferring RLSP during the trot-togallop transition did not vary with breed or sex.
Breaking from the starting gate
Trot-to-gallop transition We observed 209 racehorses across genders and breeds to examine differences in lead preferences during the trotto-gallop transition (Table 1). To test for laterality at the population level, we calculated the mean SEproportion of horses that started in their RLSP (0.91 0.004). We used a one-value t test to determine whether this value was significantly different from 0. The difference was highly significant (t test: t5 ¼ 102.8, P 0.01). We also examined whether the numbers of horses preferring their RLSP versus their LLSP differed according to breed or sex (six categories: male thoroughbreds, female thoroughbreds, male Arabians, female Arabians, male American Quarter horses, female American Quarter horses). We conducted separate tests for stride pattern choice during the trot-to-gallop transition and while breaking from the starting gate. Of the 209 horses tested, 190 (90.9%) completed the transition in their RLSP. This ratio was used to calculate the expected number of horses in each category. For example, 35 male thoroughbreds were observed during the trot-to-gallop transition. Of these, we would expect 32 to use their RLSP (90.9% of 35) and three to use their LLSP. The expected numbers were then compared with the observed values. The observed results did not differ
We observed 9116 horses across genders and breeds to examine differences in lead preferences while breaking from the starting gate (Table 2). The table shows the actual numbers as well as the proportion for each of six categories. We again calculated the mean SE proportion of horses that started in their RLSP (0.89 0.008). A onevalue t test showed the mean was significantly different from 0.5 (t test: t5 ¼ 46.5, P 0.01). We also carried out a second chi-square analysis to examine stride pattern preference when breaking from the starting gate. Of the 9116 horses observed, 90.2% (8226 of 9116) broke from the gate in their RLSP. We again used this percentage to calculate predicted numbers of horses in each of the six categories. The resulting P value was small, but not significant (chi-square test: c26 ¼ 10:7; P ¼ 0.057, power ¼ 0.70). Although the probability value was small, we calculated the power (Hintze 2004). Given the high power, we can conclude that any effect of breed or sex was slight. The decreased probability was principally due to the results from the female Arabians, probably because of the small sample size in this category. An additional 85 thoroughbred horses were observed breaking from the starting gate on racetracks in Hong Kong and Australia. Of the 85 observed, 92% preferred their RLSP and 8% preferred their LLSP. This is relevant
Table 1. Stride pattern preference during the trot-to-gallop transition Thoroughbreds
RLSP LLSP
Arabians
American Quarter horses
Male
Female
Male
Female
Male
Female
32 (0.91) 3 (0.09)
38 (0.90) 4 (0.10)
13 (0.93) 1 (0.07)
22 (0.92) 2 (0.08)
46 (0.90) 5 (0.10)
39 (0.91) 4 (0.09)
Results are shown as total numbers and proportions (in parentheses) of horses observed.
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Table 2. Stride pattern preference while breaking from the starting gate Thoroughbreds
RLSP LLSP
Arabians
American Quarter horses
Male
Female
Male
Female
Male
Female
2943 (0.91) 306 (0.09)
2791 (0.91) 273 (0.09)
70 (0.90) 8 (0.10)
41 (0.85) 7 (0.15)
1246 (0.88) 165 (0.12)
1135 (0.90) 131 (0.10)
Results are shown as total numbers and proportions (in parentheses) of horses observed.
because in Hong Kong and Australia, horses race clockwise around the track as compared to anticlockwise in U.S.A.
87.67.6. These two means were not significantly different (Mann-Whitney U test: U ¼ 67.5, N1 ¼ 27, N2 ¼ 5, P ¼ 0.69).
Multiple observations from individual racehorses A total of 32 thoroughbred racehorses, including 17 females and 15 males, were used for repeated observations breaking from the starting gate for five to seven races (Table 3). Individual racehorses are typically rested for 30 days between races, limiting the number of observations. Of the horses tested, 62.5% started every race in the same stride pattern (20/32), 31% started one race in their nonpreferred stride pattern (10/32) and 6% started two races in their nonpreferred stride pattern (2/32). When combining the preferences from all racehorses, an individual racehorse had a 94% probability that it would use its preferred stride pattern. To test for laterality on the individual level, we calculated a laterality index (LI) for each horse (Fig. 5). We first tested for laterality in general without regard to side preference by using the absolute value of LI. The mean LI value was 87.23.2. This value was significantly different from 0 (t test: t31 ¼ 27.4, P 0.01). During the repeated observation studies, horses would occasionally break from the gate in their nonpreferred stride. The mean LI for horses that preferred their RLSP most of the time was 87.1 3.6 and the mean LI for horses that preferred their LLSP most of the time was Table 3. Multiple observations from individual horses of left (L) and right (R) stride pattern preference when starting from the gate
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Females
Males
LRRRRRR RRRRRR RRRRRRR RLLLLL RRRRR RLRRRRL LLLLLLL RRRRR RRRRRRR RRRRRR RRRRRRL RRRRRR RRRRRRR LLLLLLL RRRRR RRRRRRR RRLRRRR
RRRRR RRLRRLR RRRRRR RRRRRRR RRRLRRR LLLLLLL RRRRR RRRRRR RRLRRR RRRRRRL RLRRRRR RRRRRR RRRRRRR RLLLLLL RRRLRRR
Does Stride Pattern Preference Effect How a Horse Runs in a 6-Furlong Morning Workout? We examined whether the clear stride pattern preference when first breaking into a gallop influenced the stride pattern selection during a race. Because of the difficulty in monitoring strides and stride changes during an actual race, strides were counted, and lead changes noted for 12 thoroughbreds during a 6-furlong morning workout simulating a race (see Fig. 2). The number of strides and lead changes across time for each horse are shown in Table 4. Since the 6-furlong workout begins within the clubhouse turn, all the horses began the workout in their LLSP. Upon reaching the backstretch, 11 of the 12 horses switched to the RLSP and one (horse 5) remained in the LLSP. This is approximately the percentage we would expect from the previous stride pattern preference study. None of the horses switched stride during the backstretch. Upon reaching the far turn, all the horses again switched to the LLSP, which they maintained throughout the far turn. After entering the homestretch, all 12 horses switched to their RLSP. Eight of the horses maintained their RLSP for the duration of the workout. Two horses switched back into their LLSP during the homestretch, including horse 5, which had run most of the race in its LLSP. The final two horses changed lead 20 15 Horses
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10 5 0
–100 –80 –60 –40 –20
0
20
40
60
80 100
Laterality index Figure 5. The frequency distribution of the laterality index (LI) for the right lead stride pattern (RLSP) preference in 32 horses. The distribution was bimodal, showing the pervasiveness of laterality in galloping racehorses. The mean LI for left preferred horses and right preferred horses was not significantly different.
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
Table 4. Stride pattern selection of 12 racehorses during a 6-furlong morning workout Horse 1 2 3 4 5 6 7 8 9 10 11 12
Clubhouse turn 1e5L 1e8L 1e6L 1e11L 1e3L 1e4L 1e6L 1e4L 1e3L 1e8L 1e15L
Backstretch 6e95R 9e91R 7e81R 12e90R 1e118L 4e85R 5e84R 7e93R 5e86R 4e89R 9e94R 16e84R
Far turn
Homestretch
Time (s)
96e125L 92e121L 82e120L 91e120L
126e184R 122e166R, 167e183L 121e173R 121e177R 119e141R, 142e180L 120e179R 124e135R, 136e161L, 162e185R 123e188R 121e155R, 156e164L, 165e182R 122e186R 124e183R 132e181R
115 113.2 112.3 113.4 114.1 115.1 116 113 114.3 112.4 113.3 114.2
86e119L 85e123L 94e122L 87e120L 90e121L 95e123L 85e131L
stride twice during the homestretch, from RLSP to LLSP and back to RLSP.
25
Comparison of Right Lead and Left Lead Stride Patterns in Racehorses 20
15
Length (ft)
Five horses were run anticlockwise for one-fourth to five-eighths of a mile on a standard racetrack. Each horse was observed using the left lead stride pattern while negotiating the turn. As each horse straightened out for the stretch run, they ran a few strides in the left lead stride pattern and then switched to the right lead stride pattern. Because all five horses switched to their RLSP as soon as possible, all five appeared to prefer their RLSP. The point of lead change was noted and strides immediately before and after the stride change were individually mapped according to phase (suspension or stance) on a Cartesian coordinate system. At least two strides per phase were mapped. Stride no. 1 and stride no. 2 were LLSPs immediately before a lead change. Stride no. 3 and stride no. 4 were RLSPs immediately following the lead change. A mirror image of stride no. 1 (LLSP) was produced and superimposed onto stride no. 4 (RLSP) so that hoof no. 1 (the trailing hindhoof) during strides 1 and 4 overlapped (Fig. 6). Although there was variation from horse to horse, the RLSP (triangles) and LLSP (squares) were clearly not mirror images of one another. In general, the stance phase of the LLSP appeared to be longer. To examine this more closely, we graphed the duration of the stance phase, suspension phase and total stride for the five horses (Fig. 7). There was no significant difference between the RLSP and the LLSP for stance length (paired t test: t4 ¼ 1.83, P ¼ 0.14), suspension phase length (t4 ¼ 1.25, P ¼ 0.28) or total stride length (t4 ¼ 1.21, P ¼ 0.29). Although there was not a significant difference between the lengths of the different components of the RLSP and the LLSP, in four of the five horses tested, the stance phase of the LLSP was longer than that of the RLSP, while the suspension phase of the LLSP was shorter than that of the RLSP. In two of the horses, the total length of the LLSP was shorter than that of the RLSP, whereas in the other three horses, the total length of the LLSP was longer. Finally, to examine whether the length of the stride immediately before and after a switch differed, we compared
10
5
0
–2
0
2
Width (ft) Figure 6. Comparison of the right lead stride pattern (:: RLSP) and the mirror image of left lead stride pattern (-: LLSP) in five thoroughbred racehorses. Positions of the hoofprints on the track were recorded, the LLSP was converted to a mirror image and the two stride patterns superimposed. The first hind footprints were superimposed.
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ANIMAL BEHAVIOUR, 74, 4
25
Distance (ft)
20
LLSP stance RLSP stance LLSP air RLSP air LLSP total
15 10
RLSP total
5 0
1
2
3
4
5
Horse no. Figure 7. Comparison of left (LLSP) and right lead stride pattern (RLSP) length in thoroughbred racehorses during the stance and suspension (air) phases and of total stride length for each stride pattern.
stride no. 1 (LLSP) with stride no. 2 (Fig. 8). When performing a stride switch, the horse changes stride during the suspension phase. The stance phase comparison for the normal and switch stride was not significantly different (paired t test: t4 ¼ 0.98, P ¼ 0.38), however, a significant increase was seen in both the suspension phase (t4 ¼ 7.18, P ¼ 0.002) and the total stride length (t4 ¼ 9.80, P ¼ 0.001). This result suggests that a racehorse ‘pushes off’ more strongly during the stance phase immediately preceding the switch in the suspension phase.
DISCUSSION The results from the first study clearly show that racehorses have a preference for which stride pattern to use when breaking from the standing position in the starting gate, or making the trot-to-gallop transition. Consistently across sexes and breeds, 90% of all horses observed preferred their right lead stride pattern while 10% preferred their left lead stride pattern. In addition, the results from the repeated measures test revealed that most individual racehorses preferred the same lead stride pattern most of the time. Although all the horses showed a distinct preference in the repeated measures test, occasionally a horse would start in its nonpreferred lead. This result 30
**
25 Length (ft)
948
20 15
**
10 5 0
Stance
Suspension
Total
Figure 8. Comparison of normal left lead stride patterns, LLSPs (,) , and LLSPs associated with a switch (-; horses switch stride pattern during the suspension phase). Values are means SE, N ¼ 5, paired t test: *P < 0.05.
might also be attributed to the jockey or the assistant starter holding the horse’s head to one side before breaking, thus physically influencing the horse. There is only one previous study that examined stride pattern preference in galloping horses. Deuel & Lawrence (1987) suggested that galloping horses have a preference for their LLSP. In their study, four American Quarter horses were tested while running down a 115-m straight track, and all preferred the left lead. These results appear to contrast with those of our study. It is possible that their experimental conditions influenced the choice of stride pattern, because the horses’ running was constrained to permit video monitoring. The horses’ stride pattern choice may also have been influenced by the people and equipment involved in recording the horses. Finally, it is also possible that randomly picked four horses that preferred their LLSP. Our results also appear to contrast with those of previous laterality studies in horses (McGreevy & Rogers 2005; Murphy et al. 2005; Larose et al. 2006). In these studies, laterality was sometimes seen at the individual level, but only weakly, or not at all, at the population level. Murphy et al. (2005) also showed that laterality was correlated with sex in horses. Our current study showed a strong laterality at both the individual and population levels. Furthermore, laterality did not differ between breeds and sexes. Such pervasive laterality (90% versus 10%) has only been seen in handedness in humans (reviewed in Warren 1980) and footedness in some species of parrots (reviewed in Harris 1989; Rogers 1996). Even in parrots, only certain species show a strong preference for holding food in their left foot while eating. Other species showed no preference and a few species are right-footed. It is important to stress at this point that stride pattern preference in racehorses is not a result of training. At no time during their training are racehorses ‘trained’ in a particular stride pattern. They are not ‘trained’ to leave the starting gate in a specific ‘lead’ nor are they trained to change ‘leads’ for turn negotiation, although some riders will try to force a change in stride lead patterns by shifting their weight, pulling the horse’s head to one side using the reins, or whipping the horse’ (on the shoulder, belly, or behind). At slower speeds (during training), many horses
WILLIAMS & NORRIS: STRIDE PATTERN PREFERENCE
will gallop around the turn in their right lead. Horses may learn to change leads for the turn, but they do not all change at the same location before the turn, nor do they all switch back at the same location after leaving the turn. Thus, horses change leads in the turn not because they are trained to do so but because they need to negotiate the turn at fast or full runs. This assertion is reinforced by the results observed in American Quarter horses and thoroughbreds raced in Australia and Hong Kong. American Quarter horses are almost exclusively trained on straight tracks and most run their races in one lead stride pattern. The thoroughbreds in Australia and Hong Kong are trained and race clockwise around the racetrack. In spite of this, both of these groups showed a stride pattern preference that was not significantly different from that of thoroughbreds and Arabians on American tracks. Although horses are not consciously trained to run in a particular stride pattern, there may be an unconscious influence. Riders and other handlers of horses typically approach horses always from the left side. It is possible that this behaviour might in turn influence the horse (Grzimek 1968). It is unclear whether trainers’/riders’ propensity to approach horses from the left developed from a peculiarity of the horse (they are less ‘spooked’ when approached from the left) or the humans riding the horse (usually right-handed). Larose et al. (2006) studied laterality in two breeds of horse: French Saddlebreds and Trotters. The French Saddlebreds are saddle-ridden horses and as such are traditionally approached from the left. The Trotters are harness racers and are typically approached from either side. The two breeds show exactly the same trends in laterality. Murphy et al. (2005) also found a difference in laterality based on sex. These two studies suggest that laterality is not determined solely by humans’ handling of horses in a lateralized manner. Although the horses observed in our study were not specifically trained to race in a particular stride pattern, they were intensively trained to race. The strong laterality observed in our study, but not seen in previous studies, might be a consequence of training. An untrained horse might be more likely to begin running in its nonpreferred stride than a highly trained horse. Counting of stride and lead changes during a morning workout revealed that stride pattern preference influences stride pattern usage during a race. Although racehorses are mechanically constrained to negotiate turns in their LLSP, they are free to choose either stride pattern during the straight stretches. Our results suggest that racehorses change lead stride patterns between two and four times during a 6-furlong race. These numbers are in contrast to Deuel & Lawrence (1987), who suggested that racehorses run the full race using one stride pattern. In addition, the number of lead changes observed in our study contrast strongly with those of a previously published report, which claimed that some horses may change lead stride pattern over 30 times during a race and that other horses run the entire race in the same lead pattern (Leach 1987). While running a simulated race, racehorses will spend most of their time in their preferred lead unless compelled to do otherwise (while in the turn). This was particularly apparent in horse 5, which ran almost the entire race in its LLSP. Only
at the end of the race, perhaps as the horse was tiring, did it switch stride patterns. None of the 12 horses tested ran the entire distance without switching lead stride pattern. Variation in stride pattern usage was consistent but not significantly different in five of the horses we examined. This result may prove significant with a larger sample size. A small difference in stride patterns could compound into a major effect over the course of a race. For example, should a horse have a difference of only one-eighth of an inch between the RLSP and the LLSP, going a mile using 235 strides there would be a difference of approximately 30 inches; many races are decided by only inches. Deuel & Lawrence (1987) suggested that horses running in either their RLSP or LLSP do not change the frequency of their strides, but do change the length. Thus, an increase in stride length will result in an increase in speed. Also, the stance phase is shortened and the suspension phase is lengthened during the stride change. This finding suggests that the stride change requires a special effort, and thus, that the number of stride changes during a race should be minimized for optimal performance. The domestic horse, Equus caballus, is likely to be an ideal candidate to study laterality at the population level. The horse has laterally positioned eyes with little overlap to support bilateral vision (Brooks et al. 1999; Larose et al. 2006). Previous work has suggested that animals with laterally placed eyes use them in an asymmetrical way (Evans et al. 1993; Lippolis et al. 2002, 2005; Larose et al. 2006). Vallortigara & Rogers (2005) suggested that, across many species, the left hemisphere (and the associated right sensory structures) is more involved with analytical analysis of stimuli, while the right hemisphere (and left sensory structures) is more directed towards emotional evaluations. Furthermore, horses are herd animals. It has been suggested that laterality in social animals might play a role in maintaining group integrity (Rogers 2002). Bisazza et al. (2000) examined 16 species of fish and looked for laterality in the tendency to turn in a particular direction when confronted with a predator. Of the six species that were gregarious, 100% showed a population-level laterality. Of the 10 nongregarious species, 60% showed a population-level laterality. Note, however, that the four species that were not lateralized at the population level still displayed laterality at the individual level. Finally, laterality when running in racehorses might have a biomechanical component. As stated earlier, there is a direct link between breath and stride, with exactly one breath/stride. If left and right stride patterns do not match (Deuel & Lawrence 1987; Drevemo et al. 1987), the amount of oxygen exchanged during the LLSP and the RLSP might also differ. The lungs of horses are asymmetrical, with the right, lung having an additional lobe (Getty 1975) so running in the RLSP might allow increased expansion of the right side of the chest cavity and increased oxygen exchange in the right lung. Even if the amount of oxygen exchanged during both stride patterns is the same (i.e. maximal), there still might be differences in the efficiency of the strides, causing more oxygen to be consumed in one stride pattern compared to the other. Although the 90:10 laterality ratio suggests that laterality is a primary cause for stride pattern preference, this does
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ANIMAL BEHAVIOUR, 74, 4
not preclude the possibility that consistently running in a preferred stride pattern could result in a biomechanical benefit. Given that individual racehorses prefer a particular stride pattern and that there is a correlation between stride length and breathing in racehorses, as well as constraints on stride pattern for particular parts of the racetrack (LLSP in turns, either RLSP or LLSP in straightaway), stride pattern preference might allow a horse to use the optimum sequence of stride patterns during the course of a particular race. If this is the case, stride pattern preference might not only affect performance, it might dictate performance as well. References Adams, O. R. 1979. Lameness in Horses. 3rd edn. Philadelphia: Lea & Febiger Publishing. Ades, C. & Ramires, E. N. 2002. Asymmetry of leg use during prey handling in the spider Scytodes globula (Scytodidae). Journal of Insect Behavior, 15, 563e570. Bisazza, A., Pignatti, R. & Vallortigara, G. 1997. Laterality in detour behavior: interspecific variation in poeciliid fish. Animal Behaviour, 54, 1273e1281. Bisazza, A., Cantalupo, C., Capocchiano, M. & Vallortigara, G. 2000. Population lateralization and social behavior: a study with 16 species of fish. Laterality, 5, 269e284. Brooks, D. E., Komaromy, A. M. & Kallberg, M. E. 1999. Comparative retinal ganglion cell and optic nerve morphology. Veterinary Ophthalmology, 2, 3e11. Budiansky, S. 1997. The Nature of Horses. New York: Free Press. Byrne, R. A., Kuba, M. J. & Meisel, D. V. 2004. Lateralized eye use in Octopus vulgaris shows antisymmetrical distribution. Animal Behaviour, 68, 1107e1114. Casey, M. B. 2005. Asymmetrical hatching behaviors: the development of postnatal motor laterality in the three precocial bird species. Developmental Psychobiology, 47, 123e135. Cowell, P. E., Waters, N. S. & Denenberg, V. H. 1997. Effects of early environment on the development of functional laterality in Morris maze performance. Laterality, 2, 221e232. Deuel, N. R. & Lawrence, L. M. 1987. Laterality in the gallop gait of horses. Journal of Biomechanics, 20, 645e649. Drevemo, S., Fredricson, I. & Hjerte´n, G. 1987. Early development of gait asymmetries in trotting Standardbred colts. Equine Veterinary Journal, 19, 189e191. Evans, C. S., Evans, L. & Marler, P. 1993. On the meaning of alarm calls: functional references in an avian vocal system. Animal Behaviour, 46, 23e28. Getty, R. G. 1975. Sisson and Grossman’s The Anatomy of the Domestic Animals. 5th edn. Philadelphia: W. B. Saunders. Glick, S. D. & Ross, D. A. 1981. Right-sided population bias and lateralization of activity in normal rats. Brain Research, 205, 222e225. Grzimek, B. 1968. On the psychology of the horse. In: Man and Animal: Studies in Behavior (Ed. by H. Friedrich), pp. 37e45. New York: St. Martin’s Press. Harris, L. J. 1989. Footedness in parrots: three centuries of research, theory, and mere surmise. Canadian Journal of Psychology, 43, 369e396. Hews, D. K., Castellano, M. & Hara, E. 2004. Aggression in females is also lateralized: left-eye bias during aggressive
courtship rejection in lizards. Animal Behaviour, 68, 1201e 1207. Hildebrand, M. 1977. Analysis of asymmetrical gaits. Journal of Mammalogy, 58, 131e156. Hintze, J. 2004. NCSS and PASS. Kaysville, Utah: Number Cruncher Statistical Systems. Hoyt, D. F. & Taylor, C. R. 1981. Gait and the energetics of locomotion in horses. Nature, 292, 239e240. Larose, C., Richard-Yris, M.-A., Hausberger, M. & Rogers, L. 2006. Laterality of horses associated with emotionality in novel situations. Laterality, 11, 355e367. Leach, D. H. 1987. Locomotion of the athletic horse. In: Equine Exercise Physiology. Vol. 2 (Ed. by J. R. Gillespie & N. E. Robinson), Davis, California: ICEEP Publications. Lippolis, G., Bisazza, A., Rogers, L. & Vallortigara, G. 2002. Lateralisation of predator avoidance responses in three species of toad. Laterality, 7, 163e183. Lippolis, G., Westman, W., McAllan, B. M. & Rogers, L. J. 2005. Lateralisation of escape responses in the striped-faced dunnart Sminthopsis macroura (Dasyuridae: Marsupialia). Laterality, 10, 457e470. McGreevy, P. D. & Rogers, L. J. 2005. Motor and sensory laterality in thoroughbred horses. Applied Animal Behaviour Science, 92, 337e352. Murphy, J., Sutherland, A. & Arkins, S. 2005. Idiosyncratic motor laterality in the horse. Applied Animal Behaviour Science, 91, 297e310. Muybridge, E. 1899. Animals in Motion. London: Chapman & Hall. Robins, A. & Rogers, L. J. 2004. Lateralized prey-catching responses in the cane toad, Bufo marinus: analysis of complex visual stimuli. Animal Behaviour, 68, 767e775. Rogers, L. J. 1996. Behavioral, structural and neurochemical asymmetries in the avian brain: a model system for studying visual development and processing. Neuroscience and Biobehavioral Reviews, 20, 487e503. Rogers, L. J. 2002. Advantages and disadvantages of lateralization. In: Comparative Vertebrate Lateralisation (Ed. by L. J. Rogers & R. J. Andrew), pp. 126e153. Cambridge, U.K.: Cambridge University Press. Rogers, L. J. & Andrew, R. J. 2002. Comparative Vertebrate Lateralization. Cambridge, U.K.: Cambridge University Press. Roth, E. D. 2003. ‘Handedness’ in snakes? Lateralization of coiling behaviour in a cottonmouth, Agkistrodon piscivorus leucostoma, population. Animal Behaviour, 66, 337e341. Schwarting, R. K. & Borta, A. 2005. Analysis of behavioral asymmetries in the elevated plus-maze and in the T-maze. Journal of Neuroscience Methods, 141, 251e260. Vallortigara, G. & Bisazza, A. 2002. How ancient is brain lateralization? In: Comparative Vertebrate Lateralisation (Ed. by L. J. Rogers & R. J. Andrew), pp. 9e69. Cambridge, U.K.: Cambridge University Press. Vallortigara, G. & Rogers, L. J. 2005. Survival with an asymmetrical brain: advantages and disadvantages of cerebral lateralization. Behavioral and Brain Sciences, 28, 575e633. Ventolini, N., Ferrero, E. A., Sponza, S., Chiesa, A. D., Zucca, P. & Vallortigara, G. 2005. Laterality in the wild: preferential hemifield use during predatory and sexual behaviour in the black-winged stilt. Animal Behaviour, 69, 1077e1084. Warren, J. M. 1980. Handedness and laterality in humans and other animals. Physiological Psychology, 8, 351e359. Wells, D. L. 2003. Lateralised behaviour in the domestic dog, Canis familiaris. Behavioural Processes, 61, 27e35.