Benefits and risks of barefoot harness racing in Standardbred trotters

There is a lack of research on the benefits and risks of shoeing conditions in harness racing. Thus, our objectives were to: (a) investigate whether velocity times (VT; s/km) are affected by racing unshod (N = 76,932 records on 5,247 horses); (b) determine the potential risks of galloping, being penalized, and disqualification when competing unshod (N = 111,755 records on 6,423 horses); and (c) identify additional environmental factors that affect VT and risks. VT was found to be significantly influenced by shoeing condition (e.g., unshod, shod front, shod hind, or fully shod), but also by sex, age, season, track, track condition, start method, start position, distance, and driver‐horse performance level (p < 2e‐16). The risks of galloping and disqualification were significantly influenced by shoeing condition, sex, age, season, track, start method, start position, or driver‐horse performance level (p ≤ .05). Horses racing unshod had 0.7 s/km lower VT than fully shod horses and showed better performance when racing on neutral tracks during the late summer than horses with other shoeing conditions during the same period. However, racing unshod increased the relative risks of galloping and disqualification by 15%–35% in all seasons. Horses shod only on the hind hooves showed better performance than fully shod horses, without higher risks associated with competing unshod.     

Risk factors for the hazard of lameness in Danish Standardbred trotters

A follow-up study focusing on health problems interfering with optimal training of Danish Standardbred trotters was conducted with the participation of seven professional trainers. Our aim was to estimate the incidence of health problems that cause interruptions of optimal training, and to identify associations between the hazard of lameness and selected risk factors.The study population was dynamic and contained data of 265 Standardbred trotters monitored during 5 months in 1997 and 1998. The horses were >or=2 years old. Optimal training was defined as when the horse followed scheduled training including fast-speed trotting. Interruption of optimal training could only be caused by health problems and castration.A total of 123 new events of interruption of optimal training caused by health problems were reported. Lameness (injury located to joints and tendons) was the most-frequent cause of interruption of optimal training: 84 events in 69 horses (0.09 events per horse-month). Respiratory diseases (16 events) and muscular problems (seven events) were the second and third most-frequent causes of interrupted training.The effects of trainer, gender, age-group, time with a trainer, participation in races and current month on the hazard of lameness were estimated in a multivariable Cox proportional-hazard model. The effects of trainer, gender and age-group were modelled as time-independent. The effects of time with a trainer, participation in races and the current month were modelled as time-dependent variables.Trainer affected the hazard of lameness. Geldings had higher hazard than mares, as did 3-year olds (compared to >4-year olds). Compared to the period where horses had been trained by the same trainer for >3 months, horses in the period 1.5-2.5 months after they had entered the training regime had higher risk of lameness (hazard ratio: 3.2; 95% CI: 1.1-9.9). Participation in races increased the hazard of lameness significantly in the 5 days after a races.     

Osteochondrosis and osteochondral fragments in Standardbred trotters: prevalence and relationships

Reasons for performing study: Developmental orthopaedic diseases (DOD) such as osteochondrosis (OC)/osteochondrosis dissecans (OCD), palmar/plantar osteochondral fragments (POF), ununited palmar/plantar eminences (UPE) and dorsoproximal first phalanx fragments are well recognised in the horse. Aetiopathogeneses are controversial and molecular genetic screening of DNA has recently been employed for their elucidation. Precise phenotypic definition and knowledge of breed‐specific prevalence and interrelations are essential for the interpretation of following genomic studies in Standardbred trotters. Objectives: To assess the prevalence, trend of development and interrelation of DOD in tarsocrural, metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints in Standardbred trotters. Methods: The tarsocrural and MCP/MTP joints of 464 Norwegian Standardbred yearlings were radiographed and the prevalence and interrelation of osteochondral lesions calculated. Results: Osteochondral lesions were diagnosed in 50.7% of the horses. The prevalence of tarsocrural OC/OCD at the distal intermediate ridge of the tibia (DIT) and the lateral trochlear ridge of the talus (LTT) was 19.3%. The prevalence of OC/OCD in MCP joints was 3.6%, whereas those of POF and UPE in MCP/MTP joints were 23.1 and 3.9%, respectively. Interrelation was evident for 1) most equivalent lesions in joint homologues, 2) OCD DIT and OCD LTT and 3) POF and UPE. Lesions in hock and fetlock joints were generally not significantly associated. Conclusions: The prevalence of tarsocrural OC/OCD in Norwegian Standardbreds is apparently increasing, whereas that of other articular DOD appears stable. Association analyses verify bilateralism for most equivalent lesions and suggest aetiological resemblance also between other lesions. The absence of a significant association between tarsocrural OCD and POF implies that the lesions must be considered statistically different disorders. Potential relevance: The prevalence results emphasise that DOD should be considered in Standardbred breeding regimens (e.g. by sire selection subsequent to progeny testing). Also, improved phenotypic definitions will help elucidate the true causal genes in following genomic studies.     

Skeletal muscle characteristics in young trained and untrained standardbred trotters.

Muscle biopsies were taken from the middle gluteal muscle of 28 Standardbred trotters, 3-4 years of age. The 13 horses in Group T were trained consistently from 18 months of age, whereas the 15 horses in Group UT were not exposed to any systematic training before 3 years of age. Group T horses had a lower percentage of Type IIB fibres (31%) than did Group UT horses (39%). Citrate synthase (CS) activity, representing oxidative capacity, was higher in Group T (72 mmol kg-1 min-1) than in Group UT (47 mmol kg-1 min-1). Biopsies were taken from 4 horses in each group when they were foals and then annually until 3-4 years of age. Results from this study indicate that regular training of Standardbreds from 18 months of age resulted in increased CS activity and a decrease in the percentage of Type IIB fibres. This study shows that training, not growth, is the main factor that induces a high oxidative capacity and a high Type IIA/IIB fibre ratio in muscle of Standardbred trotters.     

Histochemical properties of muscle fibres types and enzyme activities in skeletal muscles of Standardbred trotters of different ages

Fibre characteristics and enzyme activities were determined for the gluteus, semitendinosus, vastus lateralis and triceps brachii muscles of 55 Standardbred trotters of different ages. Four fibre types (I, IIA, IIB, IIC) were demonstrated by histochemical staining of myofibrillar adenosine triphosphatase after preincubation at different pH values. Type II fibres predominated in all the muscles and the type IIA/IIB ratio was higher in horses over 5 years than in younger horses, except in the vastus in which the IIA/IIB ratio did not change with age. The vastus had the highest proportion of type IIA fibres and the semitendinosus the highest proportion of type IIB fibres. Histochemical demonstration of NADH dehydrogenase disclosed that almost 100 per cent of the type IIA and many of the type I and IIB fibres were medium-stained; the remaining type I fibres were darkly stained and the type IIB fibres lightly stained. In older horses more fibres were stained for NADH dehydrogenase. The activity of triosephosphate dehydrogenase decreased that that of 3-hydroxy-acyl-coA dehydrogenase and citrate synthase increased in all the muscles except the vastus with increasing age. The greatest increase in oxidative capacity occurred in the gluteus and triceps. Training, rather than age, was regarded as the factor inducing these changes. The results emphasise that histochemical data are only semiquantitative, and there are apparent discrepancies in the intensities of histochemical staining and the biochemical evaluation of various enzymes.     

Relationships between biomechanical variables and race performance in French Standardbred trotters

Summary

Little information is available about gait characteristics and the level of performance in racehorses. The aim of that cross-sectional experiment was to study the relationships between some locomotor variables and the level of performance of trotter racehorses. A total of 104 horses from 3 to 7 years old performed a four-step locomotor test on the track with an accelerometric device: Equimetrix™. The population was divided into two groups on the basis of their official performance index: Index of TRot (ITR). These two groups were: an elite performers group (n=52) and a medium performers group (n=52). Locomotor variables: stride frequency, stance and propulsion durations, stride length, symmetry, regularity, dorsoventral, longitudinal and lateral activities were calculated at four different speeds (8.5, 11, 11.7 m/s and maximal speed). The variables were compared between two performance groups by an analysis of variance. The main results indicated that elite performers presented significantly higher stride frequency, longer stance and propulsion durations at submaximal and maximal speed. In conclusion, biomechanical characteristics of trotter racehorses, such as stride frequency and propulsion duration, might be useful criteria to quantify gait efficiency in trotter racehorses.     

Retrospective study of subchondral sclerosis and lucency in the third carpal bone of Standardbred trotters

The aim was to investigate radiographic findings of subchondral sclerosis and subchondral lucency in the dorsoproximal-dorsodistal (DPr-DDi) projection of the third carpal bone (C3) in relation to clinical appearance and to prognosis for racing. In a retrospective study, case records of 89 Standardbred trotters diagnosed with traumatic carpitis confirmed with intra-articular anaesthesia were examined. Records included data on degree of lameness at presentation and after flexion tests and a radiographic examination of the carpus, including a DPr-DDi projection of the C3. Subchondral lucency was found significantly to influence the degree of lameness at presentation and the time to start but did not significantly affect the chance of racing within 30 months post examination. In the present material no significant relationship between degree of sclerosis and lameness or prognosis for racing within 30 months was found, but the low number of C3 with severe sclerosis limited conclusions about that group.     

The use of foal and studbook traits in the breeding programmes of Finnhorse and Standardbred trotters

Genetic correlations for body measurements and subjectively scored traits between foals and studbook horses were estimated using bivariate linear mixed models. Observations for nine foal and eleven studbook traits in Finnhorses on 6529 foals and 6596 studbook horses and in Standardbred trotters on 3069 foals and 2112 studbook horses were available from the Finnish horse breeding shows. The number of sires with progeny in both foal and studbook data was 203 in Finnhorse and 145 in Standardbred trotters. Estimates of heritability for body measurements in foals and studbook horses using univariate models were high in both breeds (0.41-0.84). Heritability estimates for subjectively scored traits using univariate models were generally higher for foals (0.08-0.46) than for studbook horses (0.06-0.21) in both breeds. Genetic correlations between foals and studbook horses for body measurements were highly positive ranging from 0.74 to 0.96 in Finnhorses and from 0.79 to 0.99 in Standardbred trotters. Low to highly positive genetic correlations between foals and studbook horses for subjectively scored traits were obtained in Finnhorse trotters, whereas in Standardbred trotters genetic correlations for subjectively scored traits varied from moderately negative to highly positive. Higher estimates of heritability for foal traits and generally high genetic correlations between the foal and studbook traits indicate that an early selection for conformation traits would be efficient in the breeding programmes.     

Use of color Doppler echocardiography to assess the development of valvular regurgitation in Standardbred trotters

OBJECTIVE: To evaluate the incidence and development of valvular regurgitation and its effect on racing performance in Standardbred trotters from 2 to 3.5 years of age. DESIGN: Longitudinal observational study. ANIMALS: 103 horses. PROCEDURE: Horses were examined via echocardiographic imaging 4 times at 6-month intervals. Two-dimensional and M-mode echocardiographic examinations were performed in each horse, and color Doppler imaging was used to detect and evaluate regurgitant blood flow at each valve. RESULTS: For all cardiac valves, the frequency of valvular regurgitation increased significantly during the 18-month study period. Regurgitation was mild in all valves in which it was detected, and no progression in severity was observed at any valve. Tricuspid regurgitation was more prevalent in horses that raced regularly and was diagnosed more frequently in males and horses with larger left ventricular mass and left ventricular internal diameter during diastole. No relationship between racing performance and valvular regurgitation was observed. CONCLUSIONS AND CLINICAL RELEVANCE: The incidence of valvular regurgitation increased during the study period, and it was common at 3.5 years of age. It was not possible to determine whether the increase was a result of maturity or training. The study revealed that there is a high prevalence of mild valvular regurgitation at this age, but apparently, the regurgitation had no effect on racing performance in this age group. Whether regurgitation will progress or influence future performance is not known.     

Effects of two field continuous incremental tests on cardiorespiratory responses in Standardbred trotters

In humans, cardiorespiratory responses are widely evaluated from field incremental exercise tests. On the contrary, equine exercise physiology faces a huge lack of oxygen consumption measurements (VO₂) in field conditions due to technical concerns. The aim of this study was to test the effects of two incremental continuous field tests on cardiorespiratory responses in Standardbred trotters. The two protocols were realized at trot and ended when horses galloped. The tests started at 4.2 m/s (T1) and 6.4 m/s (T2), with speed increments of 1.4 m/s every 3 min for T1 and 0.8 m/s every 2 min for T2. Velocity (v), heart rate (HR) and gas exchanges were recorded continuously, and blood lactate concentration [La^?] was measured before and after tests. Values recorded at the end of the tests were considered as peak values. The v_peak values were 10.6 ± 0.3 and 10.7 ± 0.7 m/s for T1 and T2 respectively. Horses reached higher VO_2peak (T1: 116.6 ± 11.5 ml/min/kg; T2: 88.9 ± 10.2 ml/min/kg; p < 0.05) and HR_peak (T1: 217 ± 5 bpm; T2: 209 ± 3 bpm; p < 0.05) during T1 compared with T2. T1 was significantly longer than T2 (17.5 ± 1.9 vs. 12.9 ± 1.6 min respectively, p < 0.01), and the number of steps entirely ran tended to be different (T1: 5.6 ± 0.6; T2: 6.2 ± 0.8, p = 0.07). Compared to T2, the design of T1 appeared easier to implement and allowed higher cardiorespiratory responses. The relationship between HR‐VO₂ obtained through T1 gave a better correlation between the two variables than T2. These findings suggest that T1 might be better than T2 for evaluating cardiorespiratory adaptations to exercise and for estimating aerobic energy expenditure in exercising trotters.     

Modifications induced by training and diet in some exercise-related blood parameters in young trotters

One consequence of muscular activity is an increase in circulating lactic acid; the interval it takes to return to baseline is an index of the capability for recovery and for the utilization of this catabolyte as oxidable substrate. For the energy demand to be met the diet must provide sufficient energy; its main source for muscle activity sustaining the initial anaerobic contraction is glycogen. However, the considerable activity of aerobic muscle fibers observed in training for endurance as well as trotting races is also sustained by lipids. Their utilization is enhanced by Carnitine, which acts on the transport of fatty acids at mitochondrial level. The present study was designed to investigate the effect of L-Carnitine administration on ten 18-month long yearling (body weight 350–400kg) in pre-qualification training. Three constituted the control group; four received 9g/head/daily of L-Carnitine and three received 12g/head/daily of L-Carnitine.

The diet consisted for all subjects in 6 kg hay offered, concentrate (4kg/head/day) and soybean oil (300g/head/day) that provided 98 MJ/d of digestible energy. After one month with the new diet, they were periodically subjected to distance and speed tests. The training workload ranged from 1,600 m to 3,000 m at 650 m/min. Blood samples were collected at rest (AR), immediately after exercise (AE), 20′ (AE₁) and 60′ (AE₂) afterwards. On plasma the profiles relating to effort (lactic acid, ammonia, CK and AST) was determined. For each subject and test lactic acid production (AE-AR), and the recovery curve of lactic acid were also calculated. On the basis of a Diet*Test factorial scheme, there were no significant differences attributable to diet, while differences influenced by training were significant for lactic acid, ammonia, CK and AST.

Of particular interest was the recovery curve of lactic acid when subjects were compared singly on the basis of distance run and time. Decadence time was lowest in horses receiving the higher Carnitine dose and in the more advanced stage of training; more evidently with heavier exercise (3,000 vs 2,000 m).

In conclusion, Carnitine administration could have a favorable effect on subjects who have achieved a certain fitness condition and on the occasion of intense and prolonged effort.     

Comparative study of muscle fiber type composition in the middle gluteal muscle of andalusian, thoroughbred and arabian horses

Samples were taken from the right middle gluteal muscle of 25 Andalusian horses, 20 Thoroughbreds and 10 Arabian horses, all aged between 5-and 12-years-old and not involved in training. Histochemical analysis was carried out using myosin ATPase after acid preincubation (pH 4.4) and NADH-tr in order to determine the percentage of different fiber types. Statistical analysis showed highly significant differences (P<0.001) in the proportion of type 1 and type 2 fibers between breeds. The Thoroughbred was found to have a significantly higher proportion of type 2A fibers (P<0.001) than the other 2 breeds, although differences in the proportion of type 2B fibers in different breeds were not found to be statistically significant. The Andalusian horse was found to have a higher proportion of fast-twitch fibers of low oxidative capacity (type FT) than the other 2 breeds (P<0.001). These results not only confirm those obtained in previous studies of different breeds of horses, but highlight the histochemical differences in the skeletal muscle of breeds of great commercial and sporting interest in Spain.     

Effect of controlled exercise on middle gluteal muscle fibre composition in Thoroughbred foals

REASONS FOR PERFORMING STUDY: Most racehorses are trained regularly from about age 18 months; therefore, little information is available on the effect of training in Thoroughbred foals. HYPOTHESIS: Well-controlled exercise could improve muscle potential ability for endurance running. METHODS: Thoroughbred foals at age 2 months were separated into control and training (treadmill exercise) groups and samples obtained from the middle gluteal muscle at 2 and 12 months post partum. Muscle fibre compositions were determined by histochemical and electrophoretical techniques and succinic dehydrogenase (SDH) activity was analysed in each fibre type. RESULTS: All fibre types were hypertrophied with growth and type I and IIA fibres were significantly larger in the training than the control group at age 12 months. A significant increase of SDH activity was found in type IIX muscle fibres in the training group. CONCLUSIONS: Training in young Thoroughbred horses can facilitate muscle fibre hypertrophy and increase the oxidative capacity of type IIX fibres, which could potentially enhance stamina at high speeds. POTENTIAL RELEVANCE: To apply this result to practical training, further studies are needed to determine more effective and safe intensities of controlled exercise.     

Carnosine, anserine and taurine contents in individual fibres from the middle gluteal muscle of the camel

High muscle camosine and anserine contents contribute significantly to intra-cellular physico-chemical buffering. Our aim was to measure carnosine, anserine and taurine contents directly in individual type I, HA and IIB fibres from the middle gluteus muscle of the camel. Mean carnosine contents in type I, IIA and IIB were 24·6 ±9·2, 39·4 ±11·4 and 42·8 ±18·8 mmol kg⁻¹ dry weight (dw), respectively. Mean anserine contents in type I, HA and IIB fibres were 30·0 ±8·4, 37·3 ±10·1 and 34·5 ±9·7 mmol kg⁻¹ dw, respectively. Mean taurine contents in type I, IIA and HB fibres were 42·4 ±15-9, 203 ±12·9 and 24·7 ±15·9 mmol kg⁻¹ dw, respectively. Higher carnosine contents in type II fibres emphasise the importance of carnosine to intra-muscular acid-base regulation. A specific role for taurine in type I fibres is unclear.