Department of Medicine and Surgery, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Box 70 18, S Uppsala, Sweden.

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EQUNE VETERNARY JOURNAL Equine vet. J. (1994) 26 (2) 117-121 7 Plasa latate response to subaxial and axial exerise tests with training, and its relationship to perforane and usle harateristis in Standardbred trotters N.

1 EQUNE VETERNARY JOURNAL Equine vet. J. (1994) 26 (2) Plasa latate response to subaxial and axial exerise tests with training, and its relationship to perforane and usle harateristis in Standardbred trotters N. RONfklS, B. ESSEN-GUSTAVSSON, A. LNDHOLM and Y. ERKSSON Departent of Mediine and Surgery, Faulty of Veterinary Mediine, Swedish University of Agriultural Sienes, Box 70 18, S Uppsala, Sweden. Keywords: horse; blood; latate; usle; exerise Suary Seven young Standardbred trotters, born, raised and trained at the sae ap, perfored subaxial and axial work tests on a trak. The subaxial test onsisted of four 1,OOO runs at the trot, with inreasing speed at eah run. Eah horse perfored this test when 24, 26, 29 and 40 onths old. The axial test onsisted of trotting 1,600 and was perfored at 24 and 29 onths of age. Blood saples for plasa latate analyses were obtained after eah run, during the subaxial test and after the axial test. Musle biopsy saples were obtained at 24 and 29 onths of age. The results showed arked individual differenes in latate response to subaxial effort. Early training only appeared to influene plasa latate response in soe horses. After 40 onths of age the latate response to the final subaxial test was signifiantly lower (7.2 ov) than at 29 onths (14.5 ov). A negative orrelation was found between latate onentration after all runs in the subaxial test, and the horses speed over 1,600. No orrelations were found between latate onentration after the axial test and the horses' speed. The ativity of itrate synthase, a arker for usle oxidative apaity, inreased fro 24 to 29 onths of age. The proportion of Type B fibres dereased, whereas that of Type fibres inreased. t is onluded that latate response to a subaxial work test on a trak an be an iportant tool for evaluating perforane apaity of an individual horse. ntrodution The auulation of blood latate in response to exerise is generally regarded as an indiator of fitness and degree of training, beause it reflets the dependene on anaerobi etaboli pathways (Persson and Ullberg 1974; Jones and Capbell 1982; Persson 1983). The auulation is exponentionally related to work load, expressed as veloity. n several studies the orrelation between blood latate onentration and speed during exerise tests on the trak has been investigated. These work tests were perfored at either subaxial or axial speeds, in Standardbreds (Ashei et al. 1970; Krzywanek 1973; Persson and Ullberg 1974; Lindhol and Saltin 1974; Wilson eta/. 1983) and in Thoroughbreds (Snow and MaKenzie 1977; Kubo eta/. 1984; Bayly eta/. 1987; RonCus e? a/. 1987; Forean et a/. 1990; Lindner et a/. 1992). n soe of these reports it was suggested that horses with superior ability, or those in better ondition, tend to have lower blood latate values in response to a given work load (Kryzwanek 1973; Persson and Ullberg 1974; Snow and MaKenzie 1977; Wilson et a/. 1983; Bayly et a/. 1987). The blood latate response to a given exerise an differ arkedly between individuals and this ay be related to usle fibre properties (Valberg and EssCn-Gustavsson 1987; RonCus et a/. 1987). Musle harateristis of horses differ between individuals and with age, sex and state of training (Ronkus et a/. 1991, 1992). Standardbred trotters start to train at an early age (-18 onths). t is therefore of interest to develop a pratial field test whih an give inforation about the individual horse's physiologial apaity. The purpose of the present study was therefore to investigate usle harateristis in young Standardbred trotters undergoing training and their individual variation in plasa latate auulation in response to subaxial and axial exerise on the trak. Materials and ethods Horses Seven 2-year-old Standardbred trotters, Horses A-G (3 olts, 4 fillies) with an age variation of fl onth, were all bred, raised and trained at the sae ap. Three of the horses ould not partiipate during the whole study, whih lasted fro 24 to 40 onths of age. Horse G was lae fro the age of 29 to 39 onths and Horses C and F were sold when 3 years old. Training prograe The regular training prograe started when the horses were - 15 onths old. During the first onths, the training onsisted of slow trotting and walking. At about 18 onths of age the horses trotted slowly over a distane of 6,000-7,000, 5 days a week. n addition, one a week the horses perfored intense training on an exellent trak, where they trotted near their axiu speed, twie over a distane of 1,000. Fro the age of 22 onths, this type of ore intense training was perfored twie a week. Work tests All tests were perfored under good weather onditions and on the sae trak as was used when the horses were being trained. The sae two professional trainers handled the horses during all tests. Two types of work test were perfored, one subaxial and one axial.

2 118 Exerise, perforane and usle harateristis \:. x x x x a a E E E E nnnn it ti UJ i E -, h: 7 b: r 7 LL \: 7 Q:, 12

N. RonCus et al. 19 1 -. 401 5 30 E a, 0 - - 5 20 R d.

3 N. RonCus et al E a, R d.a 0 24onths 0 29 onths " Speed (lse) 12 Fig 2: Plasa latate onentrations afer axial work (,600 ) in relation to speed in 7 horses ( AC) at 24 and 29 onths of age. Subaxial test: This test onsisted of four 1,000- runs and the speed was inreased after eah run fro -1.50, -1.45, to ink orresponding to -9.1, -9.5, and /se. The drivers kept the speed as onstant as possible with speed hekpoints every 100. The exat speed was alulated and did not differ ore than fo.o1 /se. The tie between eah 1,000- run was.5 in. After eah run, a blood saple was obtained fro the jugular vein within 30 se. This test was perfored when the horses were 24,26,29 and 40 onths old. Maxial test: The horses trotted as fast as they ould over a distane of 1,600-, with an older horse as a 'paer' during the test. The speed was reorded and iediately after the finish a blood saple was olleted fro the jugular vein and a usle biopsy was obtained. The axial test was perfored 1 week after the subaxial test, at an age of 24 and 29 onths. Blood saples All blood saples were olleted iediately in sodiu heparin vautainer tubes (Beton-Dikinson) using a 0.8 x 40 Venojet needle. They were kept on ie until entrifugation whih was done within 6 h. Latate was then iediately analysed on plasa with a latate analyser (Analox syste, GM7). Musle biopsies Musle biopsy speiens were obtained fro the M. gluteus edius (Lindhol and Piehl 1974). The sae person took all the usle biopsies, fro a site -15 fro the tuber oxae, on a line to the root of the tail. The window of the biopsy needle was inserted to a onstant relative depth of -5, depending on the size of the horse and usle. One saple for bioheial analysis was frozen iediately in liquid nitrogen, while another saple for histoheial analyses was rolled in talu powder before being frozen. All saples were stored at -80 C until analysed. Histoheial analyses: Transverse serial setions (10 p) of the usle biopsy speien were ut in a ryostat at 0 C. These setions were stained for yosin ATPase after both aid (ph 4.3 and ph 4.6) and alkaline (ph 10.3) preinubation (Brooke and Kaiser 1970). Musle fibres were identified as type, type A or type B. Musle fibre oposition was deterined by typing at 6' - 4 A 2; Max. speed (ke) 0 24onths 0 29onths -. Fig 3: Plasa latate onentrations after suhaxin7ul speed (.OOO, 9.5 lse) in relation to axial speed (after n7j in 7 horses (A-G) at 24 and 29 onths if age. least 200 fibres. A oputerised iage analysis syste (BO-RAD, San- Bea, Hadsun, Denark) was used to alulate relative fibre distribution in nuber (%) and area (%) and ean fibre area (p2) for eah fibre type. Bioheial analyses: Freeze-dried usle saples were disseted free of fat, onnetive tissue and blood under a dissetion irosope and weighed. The ativities of itrate synthase (CS) as a arker for oxidative apaity, 3-OH-ayl-CoA dehydrogenase (HAD) as a arker for lipid oxidation, and latate dehydrogenase (LDH) as a arker for glyolyti apaity, were analysed after the saple had been hoogenised in a phosphate buffer at +25"C (Esstn et al. 1980; Esstn-Gustavsson et al. 1983). Statistial analysis All data were analysed by one-fator ANOVA repeated easures and siple linear regression. The values are given as eans k sd. Results Subaxial test The plasa latate response after the subaxial test at 24, 26 and 29 onths did not differ arkedly within horse, but large individual differenes between horses were seen (Fig ). Horses A and B showed the lowest plasa latate values in all subaxial tests. All the horses that perfored a subaxial test at 40 onths of age showed a lower latate response than in the earlier tests. The ean latate response in the final interval of the subaxial test dereased fro 14.5 to 7.2 ol/l during the training period of 16 onths (P = 0,001). Horse G, whih had been out of training for a longer period, showed only a slight derease in plasa latate onentration during this tie. Maxial test Plasa latate onentrations ranged fro 12.8 to 27.3 ol/l after the first axial test and fro 24.2 to 33.6 ol/l after the seond test. The relationship between axial speed over a distane of 1,600 and plasa latate onentrations, when the horses were 24 and 29 onths old, showed individual differenes.

4 20 Exerise, perforane and usle harateristis TABLE 1: Musle fibre harateristis and enzye ativities in. gluteus at 24 and 29 onths of age Horse A B C D E F G P o. o. o. o. o. o. o. o. o. o. o. o. o. value Fibre type ( h) HA llb Fibre area (p2) A llb Relative area (%) A Enzye (pol/g/in) s HAD LDH CS = itrate synthase; HAD = 3-OH-ayl-CoA dehydrogenase; LDH = latate dehydrogenase. No orrelation was seen between latate values after the axial test and the horse s speed at 24 or 29 onths of age (Fig 2). The horse s speed when it perfored the axial test over 1,600 was negatively orrelated with the latate values after eah run during the subaxial test at 29 onths of age (Fig 3) (Run, r =-0.91;Run2,r=-0.95;Run3,r=-0.82;Run4,r=-0.86). Musle biopsies Large individual differenes in fibre oposition were seen between the horses (Table ). The relative distribution in area of Type fibres inreased signifiantly, fro 11.5% (f5.3) to 15.2% (f3.9) during the period of 5 onths of training, while the ean perentage of Type B fibres dereased signifiantly, fro 44% (f8.4) to 37% (k7.2). The relative distribution in area of Type B fibres dereased signifiantly, fro 56% (f6.6) to 49% (f6.3). The ean CS ativity inreased signifiantly during this period fro 40 to 47 pnol/g/in (Table ). No signifiant orrelations were observed between usle harateristis and perforane or plasa latate onentrations after the work tests. Disussion Plasa latate values after a subaxial test over speeds inreasing fro 9.1 to 10.5 /se and the perforane apaity of horses over 1,600 were orrelated. This agrees with a previous study on older horses in whih axial trotting speed was orrelated with latate response after subaxial exerise at 10 lse on the trak (Persson and Ullberg 1974). The onept of an anaerobi threshold, extrapolated fro the plotted urve of blood latate onentration orrelated to speed, has been defined as the level of work just below that at whih etaboli aidosis ours, defined as VLA4 or V4 (Persson 1983; Wilson et al. 1983). During a standardised exerise test on a treadill, VLA, is said to be a useful indiation for evaluating perforane apaity and/or fitness (Persson 1983). The negative influene of age on the blood latate response to subaxial workload sees to end at aturity, whih is reahed at about 5 years of age (Persson and Ullberg 1974). There were large individual differenes in latate response to both axial and subaxial exerise in the young horses in this study, whih were all born, raised and trained at the sae ap. The relation between subaxial latate response and axiu speed was not as lear when horses were only 24 onths old as when they were 29 onths old. This is probably related to individual geneti onditions for aerobi power and fators suh as otivation, running eonoy and ability to reruit usle fibres and usle etaboli response. The plasa latate level deterined on the trak will be influened by several fators suh as surfae adherene, wind onditions, abient teperature and the ability of the driver of the sulky. However, these variables differed only inially between the work tests. Figure 2 shows that 3 of the horses (A, C and F) atually inreased their axial speed over 1,600 by 1 /se fro 24 to 29 onths of age, whereas the other 3 horses (B, D, E) showed only a sall inrease in speed. Horses A, C and F were also those showing soe hanges in the subaxial latate responses during 5 onths of training (Fig 1). A longer training period is needed, however, to obtain a arked redution in subaxial latate response, a5 seen fro the test ade in Horses A, B, D and E after 1 ore onths of training (Fig ). When training beoes ore intense, ore Type B fibres are reruited and oxidative apaity inreases in fibres (Rontus et al. 1992). No orrelation was seen between plasa latate values after the axial exerise over 1,600 and how fast the horses were able to trot. However, one study on ature Thoroughbreds has shown that the axial blood latate onentration after 1,600 ight orrespond to speed (Kubo et al. 1984). No orrelations were evident fro 24 to 29 onths of age between the horses individual usle harateristis and plasa latate values after the subaxial tests, or the perforane apaity over 1,600. However, the horses that had lower plasa latate values after the subaxial test and trotted 1,600 at a high speed were also those with a lower perentage of Type B fibres and a higher CS ativity. n previous training studies over 6 onths or ore, the Type A/B fibre ratio and Type / fibre ratio inreased (Lindhol et al. 1983; Henkel 1983; Rontus et al. 1992). Studies of shorter training periods of 5-15 weeks, however, did not reveal any hanges in usle fibre type,

5 N. Ron& rt ol. 121 although hanges were seen in usle enzye ativity (Hodgson et a/. 1985, 1986; EssCn-Gustavsson ef a/. 1989). The results of this study also support previous observations that the Type A/B fibre ratio, Type /l fibre ratio and CS ativity inrease with training. Training, not growth, is the ain fator that indues a high oxidative apaity and a high Type A/B fibre ratio in the usle of Standardbred trotters (Rontus ef a/. 1992). This study also orroborates previous observations that trained horses rely to a great extent on aerobi energy release and less latate prodution during subaxial exerise than do untrained individuals (Thornton et al. 1983; Bayly et al. 1987). Horses A and B showed the lowest plasa latate values after all subaxial tests, and these 2 horses were the first to start raing, both as 2-year-olds. Horse A was opeting best of all the horses inluded in the study during the 3-year-olds season and was ranked as one of the 15 best 3-year-old trotters that year in Sweden. Horses E and F were not ready to start until they were 4 years old. This shows how iportant the right geneti onstitution is for the young horse's early perforane apaity. Even though only a few horses were studied, it is evident that easureent of plasa latate after a subaxial work test on the trak, as a refletion of physiologial variables, an provide iportant inforation about a horse's physiologial apaity, and an be used to predit perforane. This type of inforation an also be useful for trainers for plaing a young horse at the right training level. Aknowledgeents This study was supported by the Swedish Raing board (ATG) and AGRA nsurane Copany. We thank Kerstin and Hans- Gunnar Tillander who willingly put their fine horses at our disposal. Referenes Ashei. A.. Knudsen, O., Lindhol, A,, Rulker. C. and Saltin, B. (1970) Heart rates and blood latate onentrations of Standardbred horses during training and raing. J. A. wf. ed. Ass. 157, Bayly. W.M., Grant, B.D. and Pearson, R.C. (1987) Latate onentrations in Thoroughbred horses following axial exerise under field onditions. n: Equine Exerise Physiology 2. Eds: J. R. Gillespie and N. E. Robinson. Edwards Brothers, Ann Arbor. pp Brooke, M.H. and Kaiser, K.K. (1970) Musle fibre types: How any and what kind? Arh. Neurol. 23, EssCn, B., Lindhol, A. and Thornton, J. (1980) Histoheial properties of usle fibre types and enzye ativities in skeletal usle of Standardbred trotters of different ages. Equine iw. J. 12, EssCn-Gustavsson. 8.. Lindhol, A,, MMiken. D., Persson, S.G.B. and Thornton, J. (1983) Skeletal usle harateristis of young Standardbreds in relation to growth and early training. n: Equine Exerise Physiology. Eds: D. H. Snow, S. G. 8. Persson and R.J. Rose. Granta Editions, Cabridge. pp EssCn-Gustavsson. B., MMiken. D., Karlstro, K., Lindhol, A., Persson, S.G. B. and Thornton. J. ( 1989) Musular adaptation of horses during intensive training and detraining. Equine ref. J Forean, J.H.. Bayly. B.M.. Grant. B.D. Gollnik, P.D. (1990) Standardized exerise test and daily heart rate responses of Thoroughbreds undergoing onventional rae training and detraining. A. J. ref. Res Henkel. P. (1983) Training and growth indued hanges in the iddle gluteus usle of young Standardbred Trotters. Equrne wf. J. 15, Hodgson, D.R., Rose, R.J., Diauro. J. and Allen, J.R. (19x5) Effets of a subaxial treadill training prograe on histoheial properties, enzye ativities and glyogen utilisation of skeletal usle in the horse. Eyrti~i~ wt. J Hodgson, D.R.. Rose, R.J., Diauro, J. and Allen, J.R. ( 1986) Effets of training on usle oposition in horses. An]. J. W. Res , Jones, N.L. and Capbell. E.J.M. (1982) C/ini,u/ Exrr,ise Tesriyq. W. 8. Saunder.;, London. Krzywanek, H. (1973) Studies on the evaluation of atual perforane apaity of trotters. Zenthl. Vet. Med. A. 20, Kubo. K., Takagi, S.. Murakai, M. and Kai, M. (1984) Heart rate and blood latate onentration of horses during axial work. Bull. Equine Res. /nst Lindhol, A. and Piehl, K. (1974) Fibre oposition, enzye ativity and onentration of etabolites and eletrolytes in usle of Standardbred horses. Afa wf. sand. 15, Lindhol, A. and Saltin, B. (1974) The physiologial and bioheial response of Standardbred horses to exerise of varying speed and duration. A wr..s1~and Lindhol. A,, EssCn-Gustavsson. B., MMiken. D.. Persson. S.G.B. and Thornton, J.R. ( 1983) Musle histoheistry and bioheistry of Thoroughbred horses during growth and training. n: Eqaine E\-rrise Physiology. Eds: D. H. Snow, S. G. B. Persson. and R. J. Rose. Granta Editions, Cabridge. pp Lindner, A,. von Wittke, P., Shald, M.. Kusserow. J. and Soer. H. (1992) Maxial latate onentrations in horses after exerise of different duration and intensity. J. equine iw. Si. 12, Persson, S.G.B. (1983) Evaluation of exerise tolerane and fitness in the perforane horse. n: Equine Eserise Physiolo,yy. Eds: D. H. Snow, S. G. B. Persson and R. J. Rose. Granta Editions. Cabridge. pp Persson, S.G.B. and Ullberg, L.E. (1974) Blood volue in relation to exerise tolerane in trotters. J. S. Af,: w. Ass. 45, RonCus, M., Essbn-Gustavsson, B., Lindhol, A. and Persson. S.G.B. (19x7) A field study of irulatory response and usle harateristis in young Thoroughbreds. n: Equine Eserise Physiology 2. Eds: J. R. Gillespie and N. E. Robinson. Edwards Brothers, Ann Arbor. pp x3. RonCus. M.. Lindhol. A. and Ashei, A. (1991) Musle harateristis in Thoroughbreds of different age and sexes. Equine ret. J. 23, RonCus. M., EssCn-Gustavsson, B.. Lindhol. A. and Persson. S.G.B. (1992) Skeletal usle harateristis in young trained and untrained Standardbred trotters. Equine ref. J. 24, Snow, D.H. and MaKenzie. G. (1977) Soe etaboli effets of axial exerise in the horse and adaptation with training. Equine ref../ Thornton, J., EssCn-Gustavsson, B.. Lindhol, A., MMiken, D. and Persson. S.G. B. (1983) Effets of training and detraining on oxygen uptake, ardia output. blood gas tension, ph and latate onentrations during and after exeribe in horses. n: Equine E.wrise P/.YSifJ/f>gV Eds: D.H. Snow, S. G. B. Persson and R. J. Rose. Granta Editions, Cabridge. pp Valberg, S. and EssCn-Gustavsson, 8. (1987) Metaboli response to raing deterined in pools of type, A. and B fibres. n: Eqrtiii E.t~e,r~i.si~ Physiology 2. Eds: J. R. Gillespie and N. E. Robinson. Edwards Brothers, Ann Arbor. pp, Wilson, R.G.. sler, R.B. and Thornton, J. R. (1983) Heart rate. lati aid prodution and speed during a standardized exerise test in Standardbred horses, n: Equine Exerise Physiolo,qy. Eds: D. H. Snow, S. G. B. Person and R. J. Rose. 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