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Objective—To develop an instrument that could be sandwiched between the hoof and shoe of horses and that would reliably measure vertical ground reaction forces and three-dimensional acceleration at the walk, trot, and canter.

Animals—5 clinically sound Thoroughbreds.

Procedures—The recording instrument (weight, 350 g) consisted of 2 metal plates, 2 bolts, 4 load cells, and 3 accelerometers. It was mounted to the hoof with a glue-on shoe and devised to support as much load exerted by a limb as possible. The load cells and accelerometers were wired to a 16-channel transmitter, and transmitted signals were received and amplified with a telemetry receiver.

Results—The recording instrument could measure in real time the 4 components of the ground reaction force or their resultant force along with acceleration in 3 dimensions as horses walked, trotted, or cantered on a treadmill. Patterns of force-time curves recorded for consecutive strides were similar to each other and to those previously reported, using a force plate.

Conclusions and Clinical Relevance—The recording instrument developed for use in the present study allowed us to record vertical ground reaction force and acceleration in 3 dimensions in horses at the walk, trot, and canter. (Am J Vet Res 2000;61:979–985)

Full access
in American Journal of Veterinary Research


Objective—To determine prevalence of atrial fibrillation (AF) immediately after racing among racehorses that finished well behind the winners and examine potential risk factors for AF in these horses.

Design—Case-control study.

Animals—39,302 racehorses representing 404,090 race starts in races sanctioned by the Japan Racing Association between 1988 and 1997.

Procedure—Horses that finished ≥ 4 (turf races) or 5 (dirt races) seconds behind the winner or that did not complete the race were examined for AF within 5 minutes after the race. Logistic regression and χ 2 analyses were used to determine whether sex, age, race distance, race surface, year, or development of epistaxis was associated with development of AF.

Results—Estimated minimum frequency of AF was 0.03% (123 instances of AF following 404,090 race starts), and estimated minimum prevalence of AF among racehorses was 0.29% (115 horses with AF among 39,302 racehorses). Estimated frequency of AF among horses that finished slowly or did not finish was 1.39% (120 instances of AF among 8,639 examinations), and estimated prevalence of AF in horses that finished slowly was 1.23% (92 instances of AF among 7,500 horses) or 1.01% when only the first time a horse finished slowly was considered (76 instances of AF among 7,500 horses). Atrial fibrillation was paroxysmal in most horses. Among horses that finished slowly, 4-year-old and older horses and horses that raced on turf were more likely to develop AF.

Conclusions and Clinical Relevance—Results suggest that the likelihood of AF among racehorses that finish slowly is related to age and racing surface. (J Am Vet Med Assoc 2003;223:84–88)

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in Journal of the American Veterinary Medical Association


Objective—To determine the frequency of epistaxis during or after racing among racehorses and identify factors associated with development of epistaxis.

Design—Retrospective study.

Sample Population—247,564 Thoroughbred and 4,045 Anglo-Arab race starts.

Procedure—Race start information (breed, age, sex, racing distance, and race type) was obtained for Thoroughbred and Anglo-Arab horses racing in Japan Racing Association-sanctioned races between 1992 and 1997. All horses that raced were examined by a veterinarian within 30 minutes of the conclusion of the race; any horse that had blood at the nostrils was examined with an endoscope. If blood was observed in the trachea, epistaxis related to exercise-induced pulmonary hemorrhage (EIPH) was diagnosed.

Results—Epistaxis related to EIPH was identified following 369 race starts (0.15%). Frequency of EIPHrelated epistaxis was significantly associated with race type, age, distance, and sex. Epistaxis was more common following steeplechase races than following flat races, in older horses than in horses that were 2 years old, following races ≤ 1,600 m long than following races between 1,601 and 2,000 m long, and in females than in sexually intact males. For horses that had an episode of epistaxis, the recurrence rate was 4.64%.

Conclusions and Clinical Relevance—Results suggested that frequency of EIPH-related epistaxis in racehorses is associated with the horse's age and sex, the type of race, and the distance raced. The higher frequency in shorter races suggests that higher intensity exercise of shorter duration may increase the probability of EIPH. (J Am Vet Med Assoc 2001;218:1462–1464)

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in Journal of the American Veterinary Medical Association



To determine histochemical and biochemical properties of muscle during adaptation to training on a flat or sloped track.


22 Thoroughbreds.


Samples were obtained from the middle gluteus muscle before and after training programs were conducted, using a needle-biopsy technique. Training programs consisted of horses running 1,600 m on a flat or sloped track for 16 weeks. Amplitude of middle gluteus muscle activity per burst was calculated. Muscle fiber composition and area were examined on serial cross sections processed by standard histochemical staining procedures (ATPase stain after prior incubation with an acid or base, followed by succinate dehydrogenase [SDH] stain). Furthermore, SDH and phosphofructokinase activities were determined biochemically, and composition of myosin heavy chain (MHC) isoforms was analyzed electrophoretically.


Training resulted in substantial adaptations. Relative contribution of muscle fiber with high SDH activity (type-I and -IIa fibers) to total cross-sectional area, SDH activity, and composition of MHC-IIa isoforms were increased. Gel electrophoresis revealed a large amount of MHC-IIx isoform and a small amount of MHC-IIb isoform in the muscle. Although root mean square of muscle activity for training on a sloped track was 7.6% higher than the value obtained while training on a flat track, muscle histochemical and biochemical properties did not differ significantly between groups training on flat and sloped tracks.


Training adaptations for contractile and metabolic properties of the middle gluteus muscle were evident for the 2 types of training. However, training adaptations did not differ significantly between groups trained on flat or sloped tracks. (Am J Vet Res 1999;60:1536–1539)

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in American Journal of Veterinary Research


Objective—To determine the effect of growth and training on metabolic properties in muscle fibers of the gluteus medius muscle in adolescent Thoroughbred horses.

Animals—Twenty 2-year-old Thoroughbreds.

Procedure—Horses were randomly assigned to 2 groups. Horses in the training group were trained for 16 weeks, and control horses were kept on pasture without training. Samples were obtained by use of a needle-biopsy technique from the middle gluteus muscle of each horse before and after the training period. Composition and oxidative enzyme (succinic dehydrogenase [SDH]) activity of each fiber type were determined by use of quantitative histochemical staining procedures. Whole-muscle activity of SDH and glycolytic enzyme (phosphofructokinase) as well as myosin heavy-chain isoforms were analyzed biochemically and electrophoretically, respectively.

Results—The SDH activity of type-I and -IIA fibers increased during growth, whereas whole-muscle activity was unchanged. Percentage of type-IIX/B muscle fibers decreased during training, whereas that of myosin heavy-chain IIa increased. The SDH activity of each fiber type as well as whole-muscle SDH activity increased during training. An especially noticeable increase in SDH activity was found in type-IIX/B fibers.

Conclusions and Clinical Relevance—Changes in muscle fibers of adolescent Thoroughbreds are caused by training and not by growth. The most noticeable change was for the SDH activity of type-IIX/B fibers. These changes in the gluteus medius muscle of adolescent Thoroughbreds were considered to be appropriate adaptations to running middle distances at high speeds. (Am J Vet Res 2002;63:1408–1412)

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in American Journal of Veterinary Research