Lameness in three-year-old standardbred trotters —Influence of parameters determined before three years of age

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LAMENESS IN THREE-YEAR-OLD STANDARDBRED TROTTERS - INFLUENCE OF PARAMETERS DETERMINED BEFORE THREE YEARS OF AGE G. Gaustad, DVM, PhD1; P. Kjaersgaard, MSc2; N. I. Dolvik, DVM, PhD 3

SUMMARY

The aim of the study was to use available information about a group of Standardbred trotters collected during the first three years of life to predict the risk of lameness in these horses when they reach three years of age. In a previous study on the same population, a sire index defined as the frequency of lameness within each progeny group and presence of radiographic changes other than palmar/ plantar bony fragments in the metacarpo- and metatarsophalangeal joints, were found to be significant predictors of the likelihood of developing lameness. The additional variables used in the present study were training and feeding of the horses, information that was collected retrospectively up to the time of clinical examination. A total of 265 three-year-old Standardbred trotters were randomly sampled for an epidemiological study of lameness. Eighty horses were classified as sound and 185 horses as lame, with moderate and severe signs in 138 and 47 horses, respectively. The sire index was found to be significant for predicting lameness (P<0.01), the risk of lameness increasing approximately 2.0 times for every 10% increase in,sire index. Training and dietary parameters 1 Deceased;2 MedstatResearch, N-2001 Lillestrem, Norway.3NorwegianCollegeof VeterinaryMedicine, Departmentof Large AnimalClinicalSciences, POB 8146 Dep., N-0033Oslo, Norway Acknowledgments: The authors ttlank Torsted Foundationfor economic support for this study. We extend special gratitude to Professor Reidar Birkeland for his help and to Stig karsen for valuable statistical guidance during the planning of the study and interpretation of the results. We also thank kise Gjersrud, our technician and the entire stall at the Norwegian

Authors'addresses:

College of Veterinary Medicine, Department of Large Animal Clinical

Sciences, Surgical Section. We also thank Dr. David Griffiths, Department of Morphology, Genetics and Aquatic Studies, for proofreading of the manuscript.

384

did not influence the risk of lameness significantly. Keywords: Epidemiology; equine; feeding rations; genetic influence; lameness; training

INTRODUCTION

Lameness is a frequent cause of reduced performance in Standardbred trotters. 1'2 The causative lesions may be located in joints 3'4 or in distal bones or the soft tissues, and may be due to hereditary or environmental factors. Sire index, defined as the frequency of lameness in the progeny of a sire, had in a previous study been estimated and proven to be important (P<0.01) for the prediction of the risk of developing lameness by the age of three years, s The presence of radiographic changes other than palmar/ plantar bony fragments in the metacarpo- and metatarsophalangealjoints also attributed significantly (P< 0.05). 5 Palmar/plantar bony fragments in the metacarpo- and metatarsophalangeal joints, radiographic changes in the tarsocrural joints, gender, feeding ration during the first year of life and season of birth had no influence on the risk of lameness at three years of age. s The choice of training regimen is assumed to influence the frequency of lameness .6 The higher incidence of lameness in Standardbred trotters in recent years has been connected to the tendency of having horses do less slow work such as jogging. 7 Experience shows that the intensity of training at which lameness develops is highly variable: while some horses go lame after light training, others tolerate extremely hard training and maximal effort surprisingly well. Management choices for the early training of immature animals are important if horses are to successfully endure subsequent speed training, and may be related

JOURNAL OF EQUINE VETERINARY SCIENCE

to the development of lameness. The necessity of a severe training schedule that produces the mechanical loads necessary to stimulate bone remodeling has been indicated, a However, if these training schedules are instituted too early, they may have serious deleterious effects on the distal synovial joints. In this epidemiologic study we have investigated the influence of diet and training during the second and third years of life combined with data found significant in a first year analysis s on the risk of lameness at three years of age in Standardbred trotters.

MATERIALS

AND METHODS

A random sample of 265 Norwegian-born three-yearold Standardbred trotters ( 157 females and 108 males) was used for an epidemiological study of lameness. The horses were sampled from a population of 753 animals that had been radiographically examined before 21 months of age for the presence of osteochondrosis (OC) and/or bony fragments in the tarsocrural, metacarpo- and metatarsophalangeal joints. ~-12 The sampling procedure divided the 753 horses into five groups based on the incidence of bony fragments and OC. a Surgical removal of previously detected OC and/or bony fragments was taken into account during sampling, a The first group comprised horses with bony fragments on the palmar/plantar aspect of the metacarpo- and/or metatarsophalangeal joints only. 1~ The second group comprised horses with other radiographic changes in the metacarpo- and/or metatarsophalangeal joints only. 1~ The third group comprised horses with OC in the tarsocruraljoints only. 9 The fourth group comprised horses with multiple changes, that is any combination of the previously described groups. The fifth group comprised horses with no discernible radiographic abnormalities. TM The sampled horses were clinically examined by inspection, palpation, walking, trotting and trotting after a one-minute flexion test of the carpal, stifle/tarsal and phalangeal joints separately. 15 All horses were examined at three years of age and by the same veterinarian. The degree of lameness was indicated by a fixed point scale with 0 ~ as no detected lameness and 5 ~ as not weight bearing, le Based on'the presence of spontaneous and postflexion lameness, the horses were divided into three symptom groups, group 1 being sound and groups 2 and 3 being lame with moderate and severe symptoms, respectively. The latter two groups were combined in a stepwise logistic regression to create a bivariate variable. The feeding regimens used during the second and third years of life were obtained by a questionnaire sent to the owners or trainers of all of the 265 horses. Feeding regiaGaustad G, Larsen S, Birkeland R, Dolvik NI unpublished data. bl fattening feed unit = 6.9036 MJ net energy.

Volume 16, Number 9, 1996

mens during the first year were used in the first year's analyses, s Answers were obtained from 17t and 191 horseowners/-trainers each year, respectively. The total amount of hay consumed was recorded, either ad libitum or in kilogram/day (kg/day). If hay was given it ad libitum, the average consumed amount for the second and third years was assumed to be 7 kg/day. The amounts of oats and different concentrate mixtures (kg/day) were recorded as well as different feed supplements (gram/day). Based on these recordings, daily dietary parameters were calculated for each horse. Energy consumption in fattening feed units, b digestible crude protein, calcium, phosphorus, copper, zinc, selenium, vitamin D and vitamin E was also measured. Information about training during three periods; spring and autumn at two years of age and spring at three years of age, was obtained by questionnaires sent to the owners or trainers of the 265 horses. Types and frequencies of different training methods were recorded together with the frequency of rest periods in paddock. The training methods were graded with increasing effort from no training (paddock only), walking with a jogcart, walking with a pressure wagon, jogging/trotting, trotting with a pressure wagon, interval training, to the maximum effort of 'speed training.' The frequencies of each training method were graded increasingly from 1 to 6, from once every second week, once a week, twice a week, every second day, once a day and twice a day. From these data two new training variables were calculated for each of the three periods. One, the maximum training method, expressed the maximum load of training, i.e., the training method representing the highest effort used. The second, called sum training, expressed the total amount of training. The latter parameter was calculated by summation of all registered training frequency values. Answers to questionnaires regarding training were obtained from 179, 189 and 191 horseowners/-trainers respectively for the three training periods. Based on this, the sum training was estimated for 169, 181 and 188 horses. The discrepancies in numbers of horses occurred because ten, eight and three horses respectively had not been trained at all and, therefore, had a sum training value of 0. These horses were omitted from the statistical analyses regarding sum training. The owners/trainers of horses who did not initially respond to the questionnaire were sent two reminder notices. However, data were impossible to acquire from some horses because these had changed owners/trainers, they had been stabled abroad, or information was not obtainable due to other reasons. Therefore, only 160 and 175 horses were included in the logistic regression model for the second and third years of life. Registration number, sire and dam, gender and date of birth of each horse were obtained from the Norwegian Trotting Association. 385

Statistical methods

The different types of training arc presented by counts and percentages. Sum training was compared with degree of lameness (sound, moderate and severe) using analysis of variance. Pairwise comparisons, were made with Duncan's multivariate test. 17 So also for the amounts of all daily dietary parameters. The 95% confidence intervals were calculated by using Student procedure. TM Maximum training method was compared to degree of lameness using the Kruskal-Wallis analysis of variance. 19 All tests were performed two-sided with a significance level of 5%. The sire index was defined as the percentagc of lamc horses among the progeny of each sire. All of the progeny, both sound and lame, from thc same sire were thcrcfore allotted the same sire index. The explanatory variables (radiographic groups, sire index, maximum training method, sum training and the daily dietary parameters) were entered in a multivariate logistic regression model, with two values of lameness (lame and not lame) as the dependent variable. A stepwise logistic regression proccdure was performed, with the significance level for cntry into the model of the explanatory variable set to 0.20 and significance level for exclusion from thc model to 0.05. 20 From this model the odds ratio was estimated and the 95% confidence intervals were calculated using the Student procedure. For the categorical explanatory variables that were entered into the multivariate model with more than two levels (radiographic groups and maximum training method) a coded indicator variable was needed. For example, the maximum training method was divided in 6 categories. Using cohort equals 6 as a reference category, five new dummy variables were calculated.

RESULTS S e c o n d y e a r of life

The first clinical examination revealed moderate and severe lameness in 138 and 47 horses, respectively, while 80 horses were classified as sound. For the first calculated training variable, the maximum training method during spring of the second year of life, no differences were found between sound, moderately and severely lame horses (P=0.63, Table 1). The frequency of lameness was highest among untrained horses and those subjected to the highest level of speed training and lowest for horses receiving an intermediate training intensity (jogging/trotting). Concerning the second calculated variable, sum training, no statistically significant differences were found (p=0.47, Table 2). Duncan's multivariate test for pairwise comparisons showed no differcnce between the various symptom groups (P>0.05). No differences in the dietary parameters during the second year of life were found between sound, moderately 386

Table 1. Maximum training method in spring at two years of age in 179 horses. The number of horses are given with the percentages in brackets. Walking on ajogcart and on a pressure wagon are combined and jogging/trotting and trotting on a pressure wagon are combined. Soundness

Moderate lameness

Severe Plameness value

2 (20.0)

7 (70.0)

1 (10.0)

17 (33.3) 28 (38.4) 3 (20.0) 6 (20.3)

29 29 10 20

5 (9.8) 16 (21.9) 0.63 2 (13.3) 4 (13.3)

Spring two years

No training (paddock) Walking Jogging/trotting Interval training Speed training

(56.7) (39.7) (66.7) (66.7)

Table 2 . Sum training in spring at two years of age estimated in 169 horses. Expressed as the mean with 95% confidence interval in brackets.

Spring two years

Sum training

Soundness

Moderate lameness

5.7 (5.1,6.3)

5.9 (5.4, 6.4)

Severe Plameness value

6.4 (5.3, 7.6)

0.47

lame and severely lame horses. All variables were entered in a multivariate logistic regression model. A stepwise logistic regression procedure was performed and only the sire indcx was found to contribute significantly to the model (P<0.01, Tablc 3). The estimated odds when the sire index increased 10% was 2.01 with a 95% confidence interval ( 1.65, 2.46) indicating that a 10% increase in sire index from one progeny group to another doubles the risk of being lame at three years of age (Fig. 1). The radiographic groups did not contributc to the model. Similarly, there was no significant correlation between maximum training method during the autumn and

'I

Prob (lameness)

08

0.6 /

0.4~ 0.2 10

20

30

40

50

60

70

80

90

100

Risk index (%)

Figure 1. Predicted probability of lameness as a function of sire index. JOURNAL OF EQUINE VETERINARY SCIENCE

Table 3. Logistic regression analysis for the second year of life. Regression coeff,

Standard error

-3.57 0.07

0.77 0.01

Intercept Sire index

Wsld P-value Chi-square

21.57 32.09

<0.01 <0.01

Table 5 . Sum training in autumn at two years of age estimated in 186 horses and sum training in spring at three years of age estimated in 188 horses. Expressed in mean with 95% confidence interval in brackets. Moderate Severe PSoundness lameness lameness value Autumn two years

Sum training Table 4. Maximum training method in the autumn at two years of age for 189 horses and in the spring at three years of age in 191 horses. The number of horses are given with the percentages in brackets. Walking on a jogcart and on a pressure wagon are combined and jogging/trotting and trotting on a pressure wagon are combined. Soundness

Moderate lameness

Severe Plameness value

Autumn two years

No training (paddock) Walking Jogging/trotting Interval training Speed training

0 (0.0) 8 17 5 30

(40.0) (41.5) (23.8) (28.8)

2 (66.7) 10 21 11 55

1 (33.3)

(50.0) (51.2) (52.4) (52.9)

2 (10.0) 3 (7.3) 5 (23.8) 19 (18.3)

2 (66.7)

1 (33.3)

0.38

Sum training

Table

6.

Intercept Sire index

7.6 (7.0, 8.1) 8.4 (7.9, 8.9)

8.0 (6.7, 9.4) 7.7 (6.4, 9.0)

0.41 0.38

Logistic regression analysis third year of life. Regression coeff.

Standard error___

Wald Chi-square

Pvalue

-4.08 0.07

0.79 0.01

26.96 37.30

<0.01 <0.01

The estimated odds ratio was the same as in the two years' analysis.

DISCUSSION

Spring three years

No Training (paddock) Walking Jogging/trotting Interval training Speed training

Spring three years

7.2 (6.5, 7.9) 8.6 (7.9, 9.2)

0 (0.0) 4 9 10 38

(40.0) (40.9) (38.5) (29.2)

3 8 14 73

(30.0) (36.4) (53.8) (56.2)

3 (30.0) 5 (22.7) 2 (7.7) 19 (14.6)

0.24

lameness for sound or moderately lame or severely lame horses (P=0.38, Table 4). The highest incidences of lameness tended to occur among both non-trained horses and those undergoing speed-training, although this trend was less pronounced than during the spring. There was no difference in sum-training between groups (P=0.41, Tablc 5; Duncan's multivariate test, P>0.05). T h i r d y e a r of life

There was no significant correlation between maximum training method during the spring period and lameness for sound, moderately, or severely lame horses (P= 0.24, Table 4). As in the second year, both untrained horses and those receiving speed training tended to have higher incidences of lameness, although this trend was not significant. There were no differences in the effects of sumtraining between groups. No differences between the three symptom groups were found in dietary parameters for the third year of lifc. All variables were entered in a multivariate logistic regression model. A stepwise logistic regression procedure was performed and the sire index was found to make a significant contribution to the model (P<0.01, Table 6). Volume 16, Number 9, 1996

The causes of lameness may be hereditary or environmental, or a combination of the two. We found that the sire index, combined with nutritional and training factors from the second and third years of life significantly predicted the risk of lameness at threc years of age. This implies a gcnetic factor in the development of lameness at three years of age. As an example, if respectively 30% and 40% of two half siblings groups from different sires become lame, the probability for lameness in a member of the latter group is twice that of a member of the former. This is in accordance with the first year analysis 5 and verifies the importance of the genetic factor in the development of lameness. In this study wc have used all parameters available before the time of clinical evaluation to estimate their potentials as risk factors for lameness. Since the horses were examined at three years of age, information regarding environmental factors (training and feeding) had to be collected retrospectively, which might have reduced the degree of sensivity of the study. Answers were obtained from the different owners or trainers and this may also have weakened the validity of the results as to the importance of feeding and training. The presence of radiographic changes othcr than palmar/plantar bony fragments in the metacarpo- and/or metatarsophalangeal joints (radiographic group 2) corrclatcd signifiicantly in the first year analysis with an increased risk for lameness by three ycars of agc. s When combined with the new factors of training and feeding during thc 387

second and third years, this significance vanished, indicating a decreased importance of these radiographic findings predicting lameness at three years of age. Considering the high frequency of lameness in racehorses, few studies have investigated the effect of training on bones and joints. Almost 100 years ago it was noted that bone became more densely mineralized and stronger when stressed, and lost mineralization and strength when rested. 21 This is verified in modern experiments by noninvasive techniques measuring bone density and strength in live horses. 8 Using ultrasound velocity measurement and single photon absorptiometry, it has been shown that bone responds to exercise by minimizing cortical bone porosity and increasing bone mass. The effect of immobilization and training on joints has also been documented. 8 Reduced joint cartilage results in a decrease in proteoglycan content of the joint cartilage, with subsequent softening of the cartilage and presumably increased susceptibility to injury. The main goals in training of the racehorse are to obtain good performance capability, maintain soundness throughout the training period and to make the horse fit for racing. In this study, we have investigated the connection between training and soundness by recording the incidence of lameness at three years of age. While a range of training methods are used, we have included the most common: walking with a jogcart, walking with a pressure wagon, jogging/trotting, trotting with a pressure wagon, interval training and regular speed training. Additionally, swimming, riding and working with a long rein in sand or chopped rubber are reported to be used. Few studies have addressed the connection between training methods and lameness, although new training methods and interval training have been launched to prevent lameness, r Experience indicates that certain training methods seem to provoke lameness to a greater extent than others. In this study there was no influence of maximum training method on the risk of developing lameness. However, in the spring of the second year, there was a higher frequency of lameness among both non-trained horses (paddock only) and horses trained at maximum effort. The same tendency, but not as prominent, was recorded in the two following training periods, suggesting that horses trained by the method with strongest effort are more susceptible to lameness. Regarding untrained horses (paddock rest), it is quite likely that many of these were not in training because they were already lame. Most of them should have been in training at this age, as they all were destined to race. In a study of carpitis in Norwegian cold-blooded trotters a significant correlation was found between frequency of disease, at four years of age, and training at two years of agefl a This study showed the same pattern, with a higher frequency of disease in horses receiving maximum effort in autumn of the second year of age.

388

In the present study information regarding training was collected retrospectively from different owners and trainers. A response was obtained from 67%, 71% and 72% of the study population for the three periods, respectively. One must always bear in mind that there is a wide range of opinion among horseowners concerning management. Consequently, information on how the horses were trained was difficult to interpret through a questionnaire. A bias may also have been introduced if different training regimens were used by those who answered the questionnaire and those who did not. None of the dietary parameters influenced the risk of lameness, a finding in accordance with the results of the first year analysis of the same population, s Information on feeding rations during the second and third year of life was collected when the horses were sampled for the study at three years of age, 66% and 74% of the study population, respectively. The percentages of answers for these periods were higher than for the first year study (60%). s Amounts of the different forages were given as an average for the winter period, but may well have varied within this period as the level of training was stepped up. If hay was available ad libitum, the daily intake was set to 7 kg, although this is of course an assumption and may therefore have weakened the calculations. This study has estimated the validity of different parameters for predicting the risk of lameness at three years of age. We do not know the long-term effects of the evaluated parameters on incidence of lameness in adult or in elderly horses; for this a follow-up examination of lameness, performance and durability would be necessary.

CONCLUSION

Using our observed variables from the second and third year of life, we may conclude that the sire index and, therefore, ancestry, contributes significantly (P< 0.01) to the risk of lameness at three years of age. The risk of lameness increased by a factor 2.0 for every 10% increase in the sire index. In view of the high frequency of lameness in racehorses a better training regimen with an optimized prophylactic approach to orthopedic health should be aimed. The study indicates that it may be possible to select towards sounder horses if lameness data were available for the Standardbred population. Selection of healthy strong sires is recommended if lameness in racing horses is to be prevented.

REFERENCES

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Kallthea,1985;2:448-449. 2. Bendroth M: Orsaker til I&g startfrekvens hos 3-4 ®a travh&star. Sve Vet Tidsskr 1986;38S9:1-10. 3. Rose RJ: An analysis of conditions causing lameness in the horse. Proceedings 54th Annu Aust Vet Assoc 1977;99-102. 4. Todhunter RJ, Lust G: Pathophysiology of synovitis: clinical signs and examination in horses. Continuing Education 1990;12:(7)980-992. 5. Gaustad G, Kjaersgaard P, Dolvik NI: Lameness in threeyear-old Standardbred trotters - influence of some factors available in the first year of life. J Equine Vet Sci 1995;15:233-239. 6. Lindholm A: Different Methods of training of the Standardbred trotter. Proc. of the International Conference on Equine Sports Medicine, Stockholm, Sweden,1990;36-39. 7. Gabel AA: New training methods and interval training to prevent lameness. Proc. 29th ConfAAEP 1983; 55-60. 8. Jeffcott LB: Training Effects on Bone and Joints. Proc of the International Conference on Equine Sports Medicine, Stockholm, Sweden,1990; 14-17. 9. Grendahl AM: The incidence of osteochondrosis in the tibiotarsal joint of Norwegian Standardbred trotters. A radiographic study. J Equine Vet Sci 1991 ;11:272-274. 10. Grendahl AM: The incidence of bony fragments and osteochondrosis in the metacarpo- and metatarsophalangeal joints of Standardbred trotters. A radiographic study. J Equine Vet Sci 1992;12:81-85. 11. Gr~ndahl AM: Incidence and development of ununited proximoplantartuberosity of the proximal phalanx in Standardbred

trotters. Vet radiol 1992;203(1):18-21. 12. Grendahl AM, Gaustad G, Engeland A: Progression and association with lameness and racing performance of radiographic changes in the proximal sesamoid bones of young Standardbred trotters. Equine Vet J 1994;26(2):152-155. 13. Birkeland R: Chip fractures of the first phalanx in the metatarsophalangealjoint of the horse. Acta Radiol Suppl, 1972; 319:73-77. 14. Grendahl AM, Engeland A:lnfluence of radiographically detectable orthopedic changes on racing performance in Standardbred trotters. JAm Vet Med Assoc 1995;206:1013-1017. 15. Stashak TS: Adams' Lameness in Horses, 4th Ed. Philadelphia: Lea & Febiger:Philadelphia,1987; pp.100-156. 16. ~,sheim A, Lindblad G: Intraarticular treatment of arthritis in race-horses with sodium hyaluronate. Acta vet Scand 1976;17:379-394. 17. Scheff~ H: Analysis of Variance, New York: John Wiley and Sons, Inc., 1959. 18. BhattacharyyaGK, JohnsonRA: Statistical Concepts and Methods, New York: John Wiley and Sons, Inc.,1977. 19. Lehmann EL: Nonparametrics. Statistical Methods based on Ranks. San Francisco: Holden-Day, Inc., 1989. 20. Hosmer DW, Lemeshow S: Appfied logistic regression. New York: John Wiley and Sons, Inc., 1989. 21. WollfJ: VirchowsArch PathAnatPhysiol, 1899;155,256. 22. Dolvik NI: Prevalence and risk factors in serous arthritis in the carpal joint of Norweigan coldblooded trotters. Vet Research Comm 1994;18:281-288.

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