A comparison between the trot of pony and horse foals to characterise equine locomotion at young age

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1 240 EQUINE EXERCISE PHYSIOLOGY 5 Equine vet. J., Suppl. 30 (1999) A comparison between te trot of pony and orse foals to caracterise equine locomotion at young age W. BACK*, H. C. SCHAMHARDTt#, P. R. VAN WEEREN and A. BARNEVELD Departments of General and Large Animal Surgery and tveterinary Anatomy and Pysiology, Utrect University, Yalelaan 12, NL-3584 CM Utrect, Te Neterlands. Keywords: orse; pony; Warmblood; Setland; kinematics; gait Summary Te trot at 3 d s of 24 Setland foals ( ponies ) and 24 Dutc Warmblood foals ( orses ) was recorded at age 4 monts on a treadmill using a modified CODA-3 apparatus to caracterise equine locomotion at young age. Locomotor variables of te ponies were qualitatively and, after scaling, quantitatively compared wit tose of orses. Ponies made sorter strides tan orses, evidenced by a sorter stance and swing duration, altoug teir relative stance durations were similar. Neiter linear nor dynamic scaling procedures could completely compensate for differences in eigt at te witers comparing ponies and orses. Te patterns of te joint angle-time curves were similar. Ponies ad a larger range of pro- and retraction, wit a more protracted forelimb and a more retracted indlimb, terefore demonstrating a more extended trot. Te orses trotted wit more extended elbow, stifle and rsal joints and a more flexed ip joint, wic is in accordance wit te conformation for te Warmblood. Te ponies moved wit a stiffer trot in contrast to te more supple trot of te orses, wic sowed a larger maximal fetlock extension during te stance pase. In conclusion, ponies and orses move qualitatively similarly at age 4 monts, but caracteristic breed differences in conformation and gait quality can already be detected. Scaling metods to compensate for differences in eigt at te witers cannot be applied wen animals move at te same velocity. Introduction Te gait of te young orse is one of te main factors determining its future level of performance. Foal locomotion appeared to be predictive for adult locomotion (Back et al. 1995) and as been evaluated in trotters (Drevemo et al. 1987), coldbloods (Kasper et al. 1995) and in Warmbloods (Back et al. 1994a). Tere are only a few studies in wic te locomotion of ponies as been studied kinematically (Maennicke 1961 ; Genieser 1962; Hoyt and Taylor 1979) and kinetically (Ban et al. 1995), but tis was done only in adult animals. Nowadays ponies are increasingly being used for competitive equine sports, like Autor to wom correspondence sould be addressed. Recently deceased after a tragic accident. driving and racing (Bergen and Arendonk 1993) and are terefore becoming clinically more important. Furtermore, ponies are often used in researc as a ceaper alternative to orses wen data for te equine species ave to be collected. Te aim of tis study was to compare basic stride variables of ponies and orses at a young age to verify if te gait of ponies can be considered representative of tat of orses, wic migt permit te excange of clinical and researc data concerning te locomotor apparatus. Terefore, te trot of pony and orse foals was recorded under standardised conditions at te same velocity. Linear (Giinter 1975) and dynamic (Alexander and Jayes 1983; Alexander 1984; Hof 1996) scaling procedures were applied to compare pony and orse locomotion variables in a way similar to te approac used earlier to compare foal and adult locomotion (Back et al. 1995). Materials and metods Foals After weaning at te age of 3 monts, 24 Setland pony foals ( ponies ) and 24 Dutc Warmblood foals ( orses ) were trained to walk and trot on a ig-speed treadmill. At approximately age 4 monts, wen te kinematic recordings took place, te mean eigt at te witers of te ponies was 82 cm (range: cm) and of te orses 131 cm (range: cm). Te mean weigt of te ponies was 78 kg (range: kg) and of te orses 211 kg (range: kg). Kinematic recordings Te fore and indlimb motion of te trotting ponies and orses at 3 d s, a velocity at wic foals of bot breeds were able to trot comfortably, was recorded on a treadmill using a modified CODA-3 apparatus. Tis kinematic analysis system uses potodiode markers glued to anatomically defined locations at oof and skin (Fig 1, Back et al. 1994b). On te forelimb 2 markers were fixed to te lateral oof wall: No. 1 at te toe, and No. 2 at te coronary band. Te oter markers were located at te distal (No. 3) and proximal (No. 4) ends of te metacarpus, at te distal end of te radius at te lateral styloid process (No. 5), and proximally at te site of attacment of te lateral collateral ligament of te elbow joint (No. 6), at te lateral epicondyle of te umerus (No. 7), at te caudal part of te greater tubercle (No. 8), and at te proximal end of te scapular spine (No. 9). In te

2 W. Back' ef al TABLE 1: Temporal kinematic variables of 24 pony and 24 scaled Recorded Linearly Dynamically Recorded Forelimb Stride duration (s) f 0.03*t Stance duration (s) f 0.02't Stance duration (%) rt 1.6* Swing duration (s) f 0.02.t Hindlimb Stride duration (s) f 0.03*t Stance duration (s) f 0.01*t Stance duration (%) Swing duration (s) f 0.03't *P<0.05, t = recorded mean orse value outside scaled pony range. TABLE 2: Angular kinematic variables of 24 pony and 24 Forelimb Mean Range Mean f s.d. Scapula rotation (degr.) 16.6 Protraction (degr.) 21.1 Retraction (degr.) Range of pro- & re- (degr.) 43.1 Elbow f 1.5't 19.6 * 1.4't i 1.6* 40.2 f 1.6*t 52.9 f 3.6't 29.6 * 3.1* 82.1 * 3.8* 53.5 f 3.5 Carpus * f 3.1' f f 4.3' Fetlock f 3.2' f 4.2't f * 5.0*t 'Pd.05, = recorded orse value outside pony range. indlimb, te markers on te oof and metatarsus were at similar locations as in te forelimb. Marker No. 5 was located at te distal tibia at te lateral malleolus, No. 6 at te proximal tibia at te site of attacment of te lateral collateral ligament of te stifle joint, No. 7 at te lateral epicondyle of te femur, No. 8 at te cranial part of te greater trocanter, wd No. 9 at te tuber come. Te signal of a one-dimensional accelerometer, wic was glued to te lateral oof wall of te limb to wic te CODA markers were attaced, was used to indicate te beginning of eac stride (t = 0). As only a maximum of 12 markers could be recorded at te same time, te left forelimb and te left indlimb of eac orse were analysed in different recording sessions. Eac animal underwent a warm-up on te treadmill before te actual recording of 10 seconds (3000 frames) took place. TABLE 3: Angular kinematic variables of 24 pony and 24 Hindlimb Mean Range Mean * s.d. Pelvis rotation (degr.) Protraction (degr.) Retraction (degr.) Range of pro- & re- (degr.) Hip Stifle Tarsus Fetlock f i 0.8* f 1.2.t f 1.1 *t f 4.3' i * 4.2* i *3.9*t * 3.Vt i f 4.l.t i 3.2*t f i f f 3.9* i 6.1*t f f 7.4*t *P4.05, = recorded mean orse value outside scaled pony range. From te recorded X, Y, and Z data of te different markers (No. 1-9 in te forelimb and No. 1-9 in te indlimb), te linear and temporal kinematic variables, as well as te joint angle time excursions in te sagittal plane were calculated: scapula rotation (Nos. 8,9), soulder (Nos. 7, 8,9), elbow/stifle (Nos. 5,6,7,8), carpus/tarsus (Nos. 3, 4, 5, 6), fetlock (Nos. 2, 3, 4), pelvis rotation (Nos. 8, 9), ip (Nos. 7, 8, 9). Te markers No. 9 and No. 2 on te forelimb and No. 8 and No. 2 on te indlimb were used to calculate te protraction and retraction angles. Stride lengt and frequency were linearly related to stride duration, because te velocity was kept constant in tis study. Terefore, only stride, stance and swing duration will be discussed. Stance duration was defined as te time elapsed between initial ground contact and te moment tat te fetlock joint angle was similar again to tat at initial ground contact. Segmental eigts were calculated from te difference in vertical coordinates between te proximal and distal markers on a segment at midstance. Scaling procedure Differences in eigt at te witers between te pony and orse foals influence temporal kinematics. To quantitatively compare tese variables, linear and dynamic scaling models, applied earlier to compare locomotor variables of foals and adult orses (Back et al. 1995), were used. Te linear scaling factor was = 1.6 (Gtinter 1975) and te dynamic scaling factor was d131/82 = 1.3 (Alexander and Jayes 1983; Alexander 1984; Hof 1996).

3 242 Comparison of foal locomotion in orses and ponies 1.5 Forelimb Results Conformation Te mean vertical distances between markers 1 and 8 for te ponies and orses, respectively, were 55.9 and 91.5 cm in te forelimb, and 68.0 and cm in te indlimb. Limb lengt in te orse was 1.6 times te lengt in te pony, wic is similar to teir eigt at te witers relation. At midstance, te ip joint was significantly more flexed in te orse tan in te pony (5.4 degrees difference), wile in te ponies te elbow (6.1 degrees difference), stifle (7.3 degrees difference), tarsal (9.6 degrees difference) and fetlock (10.2 and 8.0 degrees difference for fore and indlimbs respectively) joints were more flexed at midstance Horizontal distance (m) Fig la: Stick diagram at midstance relative to marker No. I on te toe. Te figures represent te mean values of te forelimbs of 24pony (square dots) and 24 orse foals (round dots), and can be considered to represent pony and orse forelimb conformation. Temporal and linear variables Te ponies made 60 cm sorter strides tan te orses (1.4 m vs. 2.0 m) because of a sorter duration of bot stance and swing pase (Table 1). Te absolute values for te orses lay between te linearly and dynamically scaled pony values, wile teir relative stance durations were similar, in bot fore and indlimbs E l v 8 C m c._ fjy U Hindlimb Horizontal distance (m) Angular variables Te angle-time diagrams were similar in sape in ponies and orses (Fig 2). However, ponies trotted wit more scapular rotation, more protraction and a larger range of pro- and retraction in te forelimbs, and more retraction and a larger range of pro- and retraction in te indlimbs (Tables 2 and 3). Te ip joint was in significantly more extended position in te orses tan in te ponies, but te range of motion was identical. Te carpal range of motion was somewat larger in te ponies because of a sligtly larger degree of bot extension and flexion. Stifle and tarsal joints of te orses were, like te soulder and elbow joints, more extended at initial ground contact. Also, te fetlock joints in bot fore and indlimbs were more extended in orses compared to ponies, bot at initial ground contact and at maximal extension. Since maximal flexion was similar, te range of fetlock joint motion was larger in orses. Fig Ib: Stick diagram at midstance relative to marker No. I on te toe. Te figures represent te mean values of te indlimbs of 24 pony (square dots) and 24 orse foals (round dots), and can be considered to represent pony and orse indlimb conformation. Comparison pony-orse Joint angle-time curves were used to qualitatively compare te locomotion patterns of ponies and orses. Quantitatively, te range in wic orse angular variable amplitudes were expected, was defined to be similar to te mean pony value plus or minus one standard deviation (s.d.). For te temporal variables, bot te mean linearly and dynamically scaled pony values * 1 s.d. from te mean were used. Any orse data outside te expected range were marked (t) in te tables (Back et al. 1995). Statistical analysis Te mean of te kinematic variables of te groups of pony and orse foals were statistically compared using a one factor ANOVA test wit a level of significance cosen at *P<0.05. Discussion Tis study sowed tat wen animals were recorded under standardised conditions, pony foal locomotion caracteristics were qualitatively similar to tose of orses. Cross-anatomical differences only resulted in small variations in joint angle variables suc as amplitude or timing of maxima and minima. Wen temporal variables were scaled to account for differences in eigt, orse foal kinematics did not matc eiter linearly or dynamically scaled pony data, but fell in between. Te total ranges of maximal pro- and retraction in fore and indlimbs were significantly larger in ponies because of more protraction in te fore- and more retraction in te indlimbs. Obviously te ponies ad to perform a more extended trot at te required velocity of 3 m/s, wile orses could move at a more collected trot (Clayton 1994; Holmstrom et al. 1995). In midstance, te elbow, stifle and tatsal joints were considerably more extended in te orses, wile te ip joint was more flexed, suggesting a more orizontal position of te femur. Tese conformational differences are likely to originate from selective breeding as tey are in agreement wit te desired

4 W. Back et al. 243 flex Soulder joint flex Elbow joint flex Carpal joint ext I -- I I I I Time (Yo of total stride duration) 1 a a7 s 80 flex g 20 C m c.g 0 7 ext Fetlock joint Fig 2a: Mean joint angle-time diagrams of te soulder; elbow, carpal and forelimb fetlock joints of 24 pony (2 and 24 orse foals (- - -) troning on a treadmill at a velocity of 3 ds flex HIP joint flex Stifle joint 60 - '0 ext ext,; 65 * I I 1 10, I0 Time (Yo of total stride duration) ~ flex Tarsal joint 60 - flex Fetlock joint a 50- F Fig 2b: Joint angle-time diagrams of te ip, stifle, tarsal and indlimb 10 I I I -60, fetlock joints of 24 pony () and 24 I orse foals (- - -) trotting on a treadmill at a velocity of 3 ds.

5 244 Comparison of foal locomotion in orses and ponies conformation for a Warmblood. Te more extended elbow joint enables enoug elbow flexion at collection and for jumping (Bennett 1992; Holmstrom et al. 1995), a more flexed ip joint results in a more protracted indlimb (Holmstrom and Pilipsson 1993), and straigter stifle and tarsal joints increase te loading capacities of te indlimb necessary for collection (Holmstrom et al. 1990; Back et al. 1996). Superior gait quality in Warmbloods as been related to greater fetlock joint extension, representing suppleness (Back et al. 1994b). Terefore, in bot fore- and indlimbs, te inbred suppleness of Warmbloods may, besides te longer moment arm and iger weigteigt ratio, account for te larger maximal fetlock joint extension in te orse foals. In conclusion, ponies and orses sow qualitatively similar movement patterns at 4 monts of age. However, conformational differences and differences in gait quality caracteristics between bot breeds can already be detected at tis age. In animals tat are trotting at te same velocity, it is not possible to convert orse kinematic data into pony data or vice versa by simple linear or dynamic scaling procedures. Acknowledgements We gratefully tank Mrs Marike Kingmans-vd Spek and Mr Joan Knaap for ousing and training of te foals, and Mr Andries Klarenbeek, Mr Jos L.M.A. Lammertink and also te veterinary students Mrs P.M. Derijks, Mrs I.D.E. van Dixoorn, Mrs A. Rutgers and Mrs M.T. Wessel for tecnical assistance. References Alexander, R.McN. (1984) Animal Mecanics, 2nd edn., Blackwell Scientific Publications, Oxford. pp Alexander, R.McN. and Jayes, A.S. (1983) A dynamic similarity ypotesis for te gaits of quadrupedal mammals. J. Zool. 201, Back, W., Scamardt, B.C. and Barneveld, A. (1996) Te influence of conformation on fore and indlimb kinematics of te trotting Dutc Warmblood orse. Pferdeeilkunde 12, Back, W., Barneveld, A,, Scamardt, H.C., Bruin, G. and Hartman, W. (1994a) Longitudinal development of te kinematics in 4.. lo-, 18-, and 26-mont-old Dutc Warmblood orses. Equine vef. J., Suppl. 17, 3-6. Back, W., Barneveld, A., Bruin, G., Scamardt, H.C. and Hartman, W. (1994b) Kinematic detection of superior gait quality in young trotting Warmbloods. Vef. Q. 16, 9-96, Back, W., Scamardt, H.C., Hartman, W., Bruin, G. and Barneveld, A. (1995) Predictive value of foal kinematics for adult locomotor performance. Res. vet. Sci. 59, Barr, A.R.S., Dow, S.M. and Goodsip, A.E. (1995) Parameters of forelimb ground reaction force in 48 normal ponies. Vet. Rec. 3, Bennett, D. (1992) Principles of Conformation Analysis, Volume 11, Fleet Street Publising Co., Gaitersburg, USA, pp Bergen, H.M.J.M. and Arendonk, J.A.M. (1993) Genetic parameters for linear type traits in Setland Ponies. Livestock Prod. Sci. 36, Clayton, H.M. (1994) Comparison of te stride kinematics of te collected, working, medium, and extended trot in orses. Equine vet. J. 26, Drevemo, S., Fredncson, I., Hjerttn, G. and McMiken, D. (1987) Early development of gait asymmetries in standardbred colts. Equine vet. J. 19, Genieser, D. (1962) Analyse der Bewegungswecsel beim Setland pony. Tesis, Giessen. Giinter, B. (1975) Dimensional analysis and teory of biological similarity. Pysiol. Rev. 55, Hof, A.L. (1996) Scaling gait data to body size. Gait and Posfure 4, Hoyt, D.F. and Taylor, C.R. (1979) Wy do ponies use different gaits wen running? Am. Zool. 19, 899. Holmstrom, M. and Pilipsson, J. (1993) Relationsips between conformation, performance and ealt in 4-year-old Swedis Warmblood riding orses. Livesrock Prod. Sci. 33, Holmstrom, M., Magnusson. L.-E. and Pilipsson. J. (1990) Variation in conformation of Swedis Warmblood orses and conformational caracteristics of elite sport orses. Equine vet. J. 22, Holmstrom, M., Fredricson, 1. and Drevemo, S. (1995) Biokinematic effects of collection on te trotting gaits in te dressage orse. Equine vet. J. 27, Kasper. C.A., Clayton, H.M., Wrigt, A.K.. Skuba, E.V. and Petrie, L. (1995) Effect of ig doses of oxytetracycline on metacarpopalangeal joint kinematics in neonatal foals. J. Am. vef. med. Ass. 207, Maennicke, E.M. (1961) er die Bewegungsvorgange des Setland ponies. Tesis, Giessen.