Objective—To determine whether race history, including
the number of races and total race distance, was
associated with risk of superficial digital flexor tendon
(SDFT) injury in Thoroughbred racehorses in Japan.
Design—Matched case-control study.
Animals—515 Thoroughbred racehorses (case horses)
that sustained an SDFT injury during training or racing
in Japan during 2002 and 951 horses (control horses)
without SDFT injury that were matched with case horses
on the basis of age and month of the latest race.
Procedure—Variables related to race history were
compared between case and control horses by
means of conditional logistic regression.
Results—The odds of SDFT injury increased as mean
race distance and mean body weight at race time
increased. Compared with females that had never competed
in steeplechase races, males regardless of
steeplechase race history and females that had competed
in steeplechase races had higher odds of SDFT injury.
Conclusions and Clinical Relevance—Results suggest
that longer mean distance per race, heavier mean body
weight at race time, steeplechase experience, and sex
(male) increased the risk of SDFT injury in Thoroughbred
racehorses. (J Am Vet Med Assoc 2004;225:90–93)
OBJECTIVE To quantify fatigue-induced electromyographic changes in hind limb muscles in horses.
ANIMALS 8 Thoroughbreds.
PROCEDURES The left and right hind limb longissimus dorsi, tensor fasciae latae, gluteus medius, and biceps femoris muscles were instrumented for surface electromyography. Hoof strain gauges were attached to confirm stride cycle. Each horse was galloped on a treadmill (grade, 3%) at a constant speed (12.6 to 14.7 m/s) to achieve fatigue after approximately 360 seconds. Before and after this exercise, the horses were trotted at 3.5 m/s. At 30-second intervals during galloping an integrated electromyography (iEMG) value for a stride and the median frequency of muscle discharge (MF) in each limb were measured. The mean of stride frequency (SF), iEMG value, and MF of 5 consecutive strides at the start and end of galloping for the lead and trailing limbs were compared. For trotting, these variables were compared at 60 seconds before and after galloping.
RESULTS The mean ± SD value for SF decreased over time (2.14 ± 0.06 to 2.05 ± 0.07 stride/s). In both the lead and trailing limbs, fatigue decreased the iEMG values of the gluteus medius and biceps femoris muscles but not those of the longissimus dorsi and tensor fasciae latae muscles. The MF did not change for any muscle during galloping with fatigue. The SF, iEMG value, and MF did not change during trotting with fatigue.
CONCLUSIONS AND CLINICAL RELEVANCE Fatigue induced by high-speed galloping decreased the gluteus medius and biceps femoris muscles' iEMG values in Thoroughbreds. Fatigue of these less fatigue-resistant hind limb muscles would affect a horse's speed.
OBJECTIVE To determine cardiorespiratory responses of Thoroughbreds to uphill and downhill locomotion on a treadmill at identical gradients.
ANIMALS 5 highly trained Thoroughbred geldings.
PROCEDURES Thoroughbreds were exercised for 2-minute intervals on a treadmill at 1.7, 3.5, 6.0, 8.0, and 10.0 m/s at a 4% incline, 0% incline (horizontal plane), and 4% decline in random order on different days. Stride frequency, stride length, and cardiopulmonary and O2-transport variables were measured and analyzed by means of repeated-measures ANOVA and Holm-Šidák pairwise comparisons.
RESULTS Horses completed all treadmill exercises with identical stride frequency and stride length. At identical uphill speeds, they had higher (vs horizontal) mass-specific O2 consumption (mean increase, 49%) and CO2 production (mean increase, 47%), cardiac output (mean increase, 21%), heart rate (mean increase, 11%), and Paco2 (mean increase, 1.7 mm Hg), and lower Pao2 (mean decrease, 5.8 mm Hg) and arterial O2 saturation (mean decrease, 1.0%); tidal volume was not higher. Downhill locomotion (vs horizontal) reduced mass-specific O2 consumption (mean decrease, 24%), CO2 production (mean decrease, 23%), and cardiac output (mean decrease, 9%). Absolute energy cost during uphill locomotion increased linearly with speed at approximately twice the rate at which it decreased during downhill locomotion.
CONCLUSIONS AND CLINICAL RELEVANCE Findings suggested that for Thoroughbreds, downhill locomotion resulted in a lower energy cost than did horizontal or uphill locomotion and that this cost changed with speed. Whether eccentric training induces skeletal muscle changes in horses similar to those in humans remains to be determined.
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.
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 χ2
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)
Objective—To determine the frequency of epistaxis
during or after racing among racehorses and identify
factors associated with development of epistaxis.
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
Objective—To determine whether warm-up exercise at different intensities alters kinetics and total contribution of aerobic power to total metabolic power in subsequent supramaximal exercise in horses.
Procedures—Horses ran at a sprint until fatigued at 115% of maximal oxygen consumption rate (
O2max), beginning at 10 minutes following each of 3 warm-up protocols: no warmup (NoWU), 1 minute at 70%
O2max (moderate-intensity warm-up [MoWU]), or 1 minute at 115%
O2max (high-intensity warm-up [HiWU]). Cardiopulmonary and blood gas variables were measured during exercise.
O2 was significantly higher in HiWU and MoWU than in NoWU throughout the sprint exercise period. Blood lactate accumulation rate in the first 60 seconds was significantly lower in MoWU and HiWU than in NoWU. Specific cardiac output after 60 seconds of sprint exercise was not significantly different among the 3 protocols; however, the arterial mixed-venous oxygen concentration difference was significantly higher in HiWU than in NoWU primarily because of decreased mixed-venous saturation and tension. Run time to fatigue following MoWU was significantly greater than that with NoWU, and there was no difference in time to fatigue between MoWU and HiWU.
Conclusions and Clinical Relevance—HiWU and MoWU increased peak values for
O2 and decreased blood lactate accumulation rate during the first minute of intense exercise, suggesting a greater use of aerobic than net anaerobic power during this period.
OBJECTIVE To determine whether racehorses undergoing regular exercise at 2 intensities or stall rest during a period of reduced training (detraining) would differentially maintain their cardiopulmonary and oxygen-transport capacities.
ANIMALS 27 Thoroughbreds.
PROCEDURES Horses trained on a treadmill for 18 weeks underwent a period of detraining for 12 weeks according to 1 of 3 protocols: cantering at 70% of maximal rate of oxygen consumption (
o2max) for 3 min/d for 5 d/wk (canter group); walking for 1 h/d for 5 d/wk (walk group); or stall rest (stall group). Standardized treadmill exercise protocols (during which cardiopulmonary and oxygen-transport variables were measured) were performed before and after detraining.
o2max, maximal cardiac output, and maximal cardiac stroke volume of all groups decreased after 12 weeks of detraining with no differences among groups. After detraining, arterial-mixed-venous oxygen concentration difference did not decrease in any group, and maximal heart rate decreased in the walk and stall groups. Run time to exhaustion and speeds eliciting
o2max and maximal heart rate and at which plasma lactate concentration reached 4mM did not change in the canter group but decreased in the walk and stall groups.
CONCLUSIONS AND CLINICAL RELEVANCE Horses following the cantering detraining protocol maintained higher values of several performance variables compared with horses following the walking or stall rest protocols. These results suggested that it may be possible to identify a minimal threshold exercise intensity or protocol during detraining that would promote maintenance of important performance-related variables and minimize reductions in oxygen-transport capacity in horses.
Objective—To evaluate sevoflurane as an inhalation
anesthetic for thoracotomy in horses.
Animals—18 horses between 2 and 15 years old.
Procedure—4 horses were used to develop surgical
techniques and were euthanatized at the end of the
procedure. The remaining 14 horses were selected,
because they had an episode of bleeding from their
lungs during strenuous exercise. General anesthesia
was induced with xylazine (1.0 mg/kg of body weight,
IV) followed by ketamine (2.0 mg/kg, IV). Anesthesia
was maintained with sevoflurane in oxygen delivered
via a circle anesthetic breathing circuit. Ventilation
was controlled to maintain PaCO2 at approximately 45
mm Hg. Neuromuscular blocking drugs (succinylcholine
or atracurium) were administered to eliminate
spontaneous breathing efforts and to facilitate
surgery. Cardiovascular performance was monitored
and supported as indicated.
Results—2 of the 14 horses not euthanatized died as
a result of ventricular fibrillation. Mean (± SD) duration
of anesthesia was 304.9 ± 64.1 minutes for horses
that survived and 216.7 ± 85.5 minutes for horses
that were euthanatized or died. Our subjective opinion
was that sevoflurane afforded good control of
anesthetic depth during induction, maintenance, and
Conclusions and Clinical Relevance—Administration
of sevoflurane together with neuromuscular
blocking drugs provides stable and easily controllable
anesthetic management of horses for elective thoracotomy
and cardiac manipulation. (Am J Vet Res