Emotional Response to Novelty and to Expectation of Novelty in Young Race Horses

The aim of this study was to estimate the emotional response to novelty and to expectation of novelty in young race horses. The novelty in this study was the first training on an automated horse walker at a new training center. To estimate the level of emotionality in horses, the telemetric measurement of heart rate (HR) was used. A hypothesis was developed that expectation of novelty can be as exciting for horses as a novelty test. In this study, 40 horses were studied just before and then during their first walk on an automated horse walker. They were divided into four groups, with 10 horses in each group. These groups were as follows: (1) 1.5-year-old Thoroughbred colts, (2) 1.5-year-old Thoroughbred fillies, (3) 2.5-year-old Purebred Arabian colts, and (4) 2.5-year-old Purebred Arabian fillies. HR was measured at rest before exercise, during handling and moving the horse from the stable, while walking on the automated horse walker for about 20 minutes, while moving the horse from the walker to the stable, and at rest after exercise. HR response to the anticipation of novelty was higher in colts than in fillies, particularly in the group of Thoroughbreds.     

Effect of ration and exercise on plasma creatine kinase activity and lactate concentration in Thoroughbred horses with recurrent exertional rhabdomyolysis

OBJECTIVE: To determine the effects of 3 rations (low grain, fat, high grain) on plasma creatine kinase (CK) activity and lactate concentration in Thoroughbred horses with recurrent exertional rhabdomyolysis (RER). ANIMALS: 5 Thoroughbreds with RER and 3 healthy Thoroughbreds (control horses). PROCEDURES: Rations were formulated to meet (low-grain and fat rations) or exceed (high-grain ration) daily energy requirements. Each ration was fed to horses in a crossover design for 3 weeks. Horses were exercised on a treadmill Monday through Friday; maximum speed on Monday and Friday was 11 m/s (6% slope), on Tuesday and Thursday was 9 m/s, and on Wednesday was 4.5 m/s. Plasma CK activity and lactate concentration were determined before and after exercise. RESULTS: Horses with RER fed the high-grain ration had significantly greater CK activity and change in CK activity 4 hours after exercise, compared with those fed the low-grain ration. Horses with RER exercised at the trot or canter had significantly greater increases in CK activity, compared with those exercised at the gallop. Plasma lactate concentrations after exercise were similar in control and affected horses. Lactate concentration and CK activity were not correlated in horses with RER. CONCLUSIONS AND CLINICAL RELEVANCE: Rations high in grain and formulated to exceed daily energy requirements may increase episodes of rhabdomyolysis in thoroughbred horses susceptible to RER.     

Comparison of the blood plasma catecholamines level in thoroughbred and Arabian horses during the same-intensity exercise

The aim of this study was to compare changes in epinephrine (E), norepinephrine (NE) and dopamine (DA) levels in blood plasma of two racehorses breeds: Arabian and Thoroughbred during moderate intensity exercise performed in the same conditions. The increase in plasma E level just after exercise was higher in Thoroughbreds than in Arabians. During the whole test, the Arabians showed the higher levels of NE and DA as compared to those found in Thoroughbreds.     

Frequency domain analysis of heart rate variability in horses at rest and during exercise

The pattern of variation in heart rate on a beat-to-beat basis contains information concerning sympathetic (SNS) and parasympathetic (PNS) contributions to autonomic nervous system (ANS) modulation of heart rate (HR). In the present study, heart period (RR interval) time series data were collected at rest and during 3 different treadmill exercise protocols from 6 Thoroughbred horses. Frequency and spectral power were determined in 3 frequency bands: very low (VLF) 0-< or = 0.01, low (LO) >0.01-< or = 0.07 and high (HI) >0.07-< or = 0.5 cycles/beat. Indicators of sympathetic (SNSI = LO/HI) and parasympathetic (PNSI = HI/TOTAL) activity were calculated. Power in all bands fell progressively with increasing exercise intensity from rest to trot. At the gallop VLF and LO power continued to fall but HI power rose. SNSI rose from rest to walk, then fell with increasing effort and was lowest at the gallop. PNSI fell from rest to walk, then rose and was highest at the gallop. Normalised HI power exceeded combined VLF and LO power at all gaits, with the ratio HI to LO power being lowest at the walk and highest at the gallop. ANS indicators showed considerable inter-horse variation, and varied less consistently than raw power with increasing physical effort. In the horses studied, the relationship between power and HR changed at exercise intensities associated with heart rates above approximately 120-130 beats/min. At this level, humoral and other non-neural mechanisms may become more important than autonomic modulation in influencing heart rate and heart rate variability (HRV). HRV at intense effort may be influenced by respiratory-gait entrainment, energetics of locomotion and work of breathing. HRV analysis in the frequency domain would appear to be of potential value as a noninvasive means of assessing autonomic modulation of heart rate at low exercise intensities, only. The technique may be a sensitive method for assessing exercise response to experimental manipulations and disease states.     

Influence of Acute Exercise on Serum Homocysteine in Horse

The effect of acute exercise on serum homocysteine (sHCy) concentration was examined in 10 horses; five Sella Italiana and five Thoroughbreds. All horses underwent standard training before the study (show jumping for Sella Italiana horses and gallop racing for Thoroughbreds). For the study, blood samples were taken at rest, immediately after exercise, and during a recovery period (30 and 60 minutes after exercise) by external jugular venipuncture. sHCy values were determined by high-performance liquid chromatography. Heart rate and blood lactate were monitored to quantify the workloads. In show jumpers, there was a significant effect of sampling time on sHCy (P < .01), which increased significantly after exercise as compared with at rest. In Thoroughbreds, no statistically significant differences were observed in sHCy over time (F_(3,12) = 0.89, P = .05). The baseline values of sHcy were higher in Thoroughbreds than in show jumpers (P < .0002). We infer that physical activity causes biochemical changes that can influence the metabolic pathway of homocysteine in show jumpers, whereas the absence of a significant effect of exercise in Thoroughbreds may reflect an adaptive response of the enzymatic antioxidant defense system.     

Resting concentrations of cardiac troponin I in fit horses and effect of racing

ObjectivesTo determine normal resting values for cardiac troponin I (cTnI) in healthy Standardbred, Thoroughbred and Warmblood horses and investigate if racing has an influence on cTnI concentrations.BackgroundMeasuring cTnI concentrations in plasma is the gold standard for detecting myocardial injury in humans. Cardiac troponin I is highly conserved between species and has gained interest as a marker for cardiac injury in horses. Increased levels of cTnI have been reported in association with endurance and short-term strenuous exercise on a treadmill in horses. However, the effect of true racing conditions has not yet been reported.Animals, materials and methodsBlood samples for analysis of cTnI concentrations in plasma were collected from 67 Standardbred racehorses, 34 Thoroughbred racehorses and 35 Warmblood dressage horses at rest. Blood samples were also collected prior to and after racing in 22 Standardbred racehorses and 6 Thoroughbred racehorses.ResultsAll horses except one had resting plasma cTnI concentrations <0.022 μg/L. Mild increases in cTnI concentrations were seen in some horses 1–2 h after the race (1/17 Standardbreds and 2/6 Thoroughbreds) as well as 10–14 h after the race (4/21 Standardbreds and 1/6 Thoroughbreds).ConclusionsResting cTnI concentrations in horses are low but mildly elevated cTnI concentrations may be detected in some horses 1–14 h after racing. These findings could be of importance when evaluating horses with suspected cardiac disease that recently have performed hard exercise.     

The Effect of Different Physical Exercise on Plasma Leptin,Cortisol, and Some Energetic Parameters Concentrations in Purebred Arabian Horses

Leptin is a hormone that coordinates food intake, energy expenditure, and metabolic rate; it is, however, unknown how exercise influences plasma leptin concentration in horses. The aim of the study was to evaluate the exercise-induced changes in plasma leptin concentration in purebred Arabian horses competing in races and endurance rides. A total number of 26 horses (12 purebred Arabian racehorses aged 3–5 years and 14 endurance horses aged 7–14 years) were studied during performing routine physical exercise. From each horse, blood samples were collected at rest and immediately after the exercise session. Concentrations of plasma leptin, cortisol, lactic acid, uric acid, triacylglycerols, glycerol and free fatty acids were determined. Exercise-induced increase in cortisol and free fatty acid values were higher in endurance horses than in racehorses. Neither endurance nor race exercises influenced the plasma leptin concentration. Further research is needed to elucidate the effects of different types of exercise on leptin synthesis and secretion in horses.     

Aquapuncture Improves Metabolic Capacity in Thoroughbred Horses

The aim of this study was to evaluate the effect of aquapuncture on muscle enzymes release and cardiovascular and metabolic variables of Thoroughbred horses during and after exercise. Eighteen healthy Thoroughbred horses, submitted to training for competition, were used. The animals were randomly allotted into three groups: ConG (negative control group), ShG (sham aquapuncture or positive control group), and AcuG (treatment aquapuncture group). The treatments were done twice per week, during a 3-week interval. Physical performance was evaluated under field conditions, with two submaximal incremental velocity tests, separated by a 3-week period. The tests included evaluation of cardiovascular (V₂₀₀) and metabolic (V_La4) capacities and measurement of creatine kinase (CK) and aspartate aminotransferase (AST) before and after exercise. V₂₀₀ values were not different between times or groups. V_La4 values were statistically greater after treatment for the AcuG group compared with pretreatment. CK concentrations were statistically greater after exercise for all groups, and AST concentrations were not different between times or groups. Aquapuncture influenced neither cardiovascular capacity nor the release of muscle enzymes; however, it did improve metabolic capacity of Thoroughbred horses.     

Plasma Coenzyme Q10 and Tocopherols in Thoroughbred Race Horses: Effect of Coenzyme Q10 Supplementation and Exercise

The fundamental role of coenzyme Q10 (CoQ10) in cellular bioenergetics is well established in humans and several other species, yet there is no information about its role in horses. In continuation of our study of serum CoQ10 in Thoroughbred race horses, we examined the effect of CoQ10 supplementation and exercise on changes in plasma CoQ10 and α- and γ-tocopherol concentrations. Two groups of horses, five per group, were used. One group received 1.9 g of CoQ10 daily and the second group 3.4 g as a dietary supplement. Both groups were subjected to graduated training sessions that involved low-intensity exercise (gallop) followed by high-intensity exercise (breeze). CoQ10 supplementation resulted in a significant increase in plasma CoQ10 during low-intensity exercise, whereas the increase following high-intensity exercise was markedly attenuated in both groups (P < .05). There were no changes in plasma α- and γ-tocopherol concentrations following the two exercise sessions. γ-Tocopherol constituted approximately 5% of α-tocopherol; this is the first report of plasma γ-tocopherol in horses. The attenuated response of plasma CoQ10 in horses receiving CoQ10 supplementation following high-intensity exercise may be attributed to its consumption during severe oxidative stress. This finding indicates that in horses not receiving any CoQ10 supplementation, high-intensity exercise would result in a marked depletion of endogenous CoQ10 in plasma, which could compromise their health and physical performance. This documents the importance of CoQ10 in horses. The study also establishes the safety and tolerability of high-dose CoQ10 in Thoroughbred race horses.     

Stress fractures of the tibia and humerus in Thoroughbred racehorses: 99 cases (1992-2000)

OBJECTIVE: To determine clinical characteristics of and outcome in Thoroughbred racehorses with tibial or humeral stress fractures. DESIGN: Retrospective study. ANIMALS: 99 Thoroughbreds with tibial or humeral stress fractures. PROCEDURE: Information obtained from the medical records included history, signalment, and clinical, radiographic, and scintigraphic findings. Outcome was determined by interviewing trainers, performing follow-up examinations, and analyzing race records. RESULTS: Seventy-four tibial stress fractures were identified in 61 Thoroughbreds, and 48 humeral stress fractures were identified in 39 Thoroughbreds (1 horse was included in both groups). Tibial stress fractures occurred most commonly in 2-year-old or unraced horses. Fractures were located in 1 of 3 sites in the tibia (most commonly, the caudolateral cortex of the mid-diaphysis) and 1 of 4 sites in the humerus (most commonly, the caudodistal cortex). Forty-four of 58 (76%) tibial stress fractures and 18 of 32 (56%) humeral stress fractures were identified radiographically. Humeral stress fractures involving the caudodistal cortex were not detected radiographically. Treatment consisted of rest and exercise restriction, and 49 of 61 (80%) horses with tibial stress fractures and 30 of 39 (77%) horses with humeral stress fractures returned to racing. Humeral stress fractures recurred in 6 horses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that in Thoroughbred racehorses, tibial stress fractures occurred most commonly in unraced 2 year olds, whereas humeral fractures occurred most commonly in older horses that had raced previously. The prognosis for racing following treatment was good.     

The influence of betaine on untrained and trained horses exercising to fatigue

Because exercise fatigue has been associated with the accumulation of lactic acid, factors that influence lactate metabolism during exercise can potentially enhance performance. The objective of this study was to examine the effects of supplemental betaine on eight mature Thoroughbred horses before and after 8 wk of conditioning. The effects of betaine were tested in two cross-over design experiments, allowing each horse to receive both the control and betaine treatments at each fitness level. Ingestion of 80 mg of betaine/kg of BW for 14 d before exercise testing did not alter plasma lactate, glucose, free fatty acids (FFA), or triglyceride concentrations during exercise in the untrained or trained horses. A time x treatment interaction (P < .05) was observed for plasma lactate in untrained horses during recovery from exercise, and plasma lactate concentrations were lower (P < .05) at 60 min after exercise when untrained horses received betaine. Plasma FFA concentrations were lower (P < .05) before exercise and at 720 min after exercise when untrained horses received betaine. These data indicate that betaine may influence lactate metabolism following exercise in untrained horses; however, betaine does not seem beneficial for trained horses.     

Effect of oral administration of dantrolene sodium on serum creatine kinase activity after exercise in horses with recurrent exertional rhabdomyolysis

OBJECTIVE: To determine the effect of oral administration of dantrolene sodium on serum creatine kinase (CK) activity after exercise in horses with recurrent exertional rhabdomyolysis (RER). ANIMALS: 2 healthy horses and 5 Thoroughbreds with RER. PROCEDURE: 3 horses received 2 doses of dantrolene (4, 6, or 8 mg/kg, p.o., with and without withdrawal of food) 2 days apart; 90 minutes after dosing, plasma dantrolene concentration was measured spectrofluorometrically. On the basis of these results, 5 Thoroughbreds with RER from which food was withheld received dantrolene (4 mg/kg) or an inert treatment (water [20 mL]) orally 90 minutes before treadmill exercise (30 minutes, 5 d/wk) during two 3-week periods. Serum CK activity was determined 4 hours after exercise. Plasma dantrolene concentration was measured before and 90 minutes after dosing on the first and last days of dantrolene treatment and before dosing on the first day of the inert treatment period, RESULTS: 90 minutes after dosing, mean +/- SEM plasma dantrolene concentration was 0.62 +/- 0.13 and 0 microg/mL in the dantrolene and inert treatment groups, respectively. Serum CK activity was lower in dantrolene-treated horses (264 +/- 13 U/L), compared with activity in water-treated horses (1,088 +/- 264 U/L). Two horses displayed marked muscle stiffness on the inert treatment. CONCLUSIONS AND CLINICAL RELEVANCE: In 5 horses with RER from which food had been withheld, 4 mg of dantrolene/kg administered orally provided measurable, though variable, plasma concentrations and significantly decreased serum CK activity after exercise in 4 of those horses.     

Biochemical and antioxidant changes in plasma and erythrocytes of pentathlon horses before and after exercise

Abstract: Physical exercise in the horse induces a series of normal physiological and biochemical adaptations. Increasing metabolism and oxygen uptake may induce oxidative stress in various organs. The aim of this study was to examine exercise-induced changes in some plasma and RBC biochemical and antioxidant variables in pentathlon horses. Blood samples were taken from 14 horses before, immediately after, and 24 hours after competing in two 1-minute runs of intense exercise over jumps. The peak intensity periods were preceded by a 20-minute warm-up and separated by a 20-minute break. The following plasma biochemical analytes were determined: total protein, uric acid, and lactate concentrations, and lactate dehydrogenase (LDH) and creatine kinase (CK) activities. Total antioxidant status (TAS) and the ferric reducing ability of plasma (FRAP) also were measured. Thiobarbituric acid-reactive substances (TBARS), reduced glutathione (GSH), and total protein concentrations, and glutathione peroxidase (GSHPx) and superoxide dismutase (SOD) activities were determined in RBC hemolysates. Significantly increased concentrations of total protein, lactate, and FRAP, and increased activities of CK and LDH were observed immediately postexercise compared with pre-exercise samples (P < .05). All results returned to approximately initial values after 24 hours of rest. RBC GSH and TBARS concentrations did not change immediately after exercise, but decreased after 24 hours of rest (P < .05). Plasma uric acid and FRAP values were positively correlated in a linear model ( r = .78). In summary, the type of exercise applied in this study, which can be considered quite usual for pentathlon horses, caused detectable biochemical and lipid peroxidative changes in plasma and RBCs. FRAP and TAS values changed in opposite directions, indicating that when antioxidant capacity is assessed using different methods, highly different results may be obtained.     

Changes in salivary and plasma cortisol levels in Purebred Arabian horses during race training session

Physical activity and stress both cause an increase in cortisol release ratio. The aim of this study was to evaluate the use of saliva samples for the determination of cortisol concentrations indicating the work‐load level in horses during race training. Twelve Purebred Arabian horses aged 3–5 years were studied during the routine training session. After the warm‐up, the horses galloped on the 800 m sand track at a speed of 12.8 m/s. Three saliva samples, and three blood samples were collected from each horse. Both types of samples were taken at rest, immediately after return from the track and after 30 min restitution. The concentrations of blood lactic acid (LA), and cortisol in saliva and plasma samples were measured and analyzed. Blood LA, plasma and salivary cortisol levels increased significantly after exercise (P < 0.05). Salivary cortisol concentration determined 30 min after the exercise correlated significantly with plasma cortisol level obtained immediately after exercise (P < 0.05) as well as measured 30 min after the end of exercise (P < 0.05). The determination of cortisol concentration in saliva samples taken from racehorses 30 min after the end of exercise can be recommended to use in field conditions to estimate the work‐load in racehorses.     

Do Thoroughbred and Standardbred horses have similar increases in pulmonary vascular pressures during exertion?

To test the hypothesis that the pulmonary vascular pressures of Thoroughbred and Standardbred horses behave similarly during exertion. Measurements were made on 5 Thoroughbred and 5 Standardbred horses on a treadmill at rest and during 3-minute exercise intervals at speeds predicted to produce 75%, 90%, and 100% maximal heart rate. Left forelimb acceleration, heart rate, esophageal pressure, and pulmonary artery pressure were measured continuously. Pulmonary capillary and wedge pressures were measured during intermittent occlusion of the pulmonary artery. Breathing rate and gait frequency were the fundamental frequencies of the esophageal pressure and limb acceleration signals respectively. The ratio of speed:gait frequency gave stride length. The effects of exertion and breed were evaluated using two-way analysis of variance. Exertion produced significant increases in pulmonary artery (P = 0.001), capillary (P= 0.002), and wedge (P= 0.005) pressures. No significant effect of breed was detected on pulmonary artery pressure, but at exertion pulmonary capillary and wedge pressures were 15% (P= 0.03) and 23% (P= 0.04) greater in Thoroughbreds, respectively. Treadmill speed was ~12% greater (P= 0.04), stride length was ~25% greater (P= 0.0003), gait frequency was ~10% less (P= 0.006), breathing rate was ~10% less (P= 0.001), and heart rate was ~6% less (P= 0.06) for Thoroughbreds. There was no effect of breed on inspiratory or expiratory esophageal pressure although mean esophageal pressure was ~2 mmHg greater (P= 0.03) in exercising Standardbreds. In conclusion, pulmonary capillary and wedge pressures are greater in Thoroughbreds than in Standardbreds at similar fractions of maximal heart rate. This is compatible with the higher incidence of exercise-induced pulmonary hemorrhage observed in Thoroughbreds.     

Pharmacokinetics of detomidine administered to horses at rest and after maximal exercise

Reason for performing study: Increased doses of detomidine are required to produce sedation in horses after maximal exercise compared to calm or resting horses. Objectives: To determine if the pharmacokinetics of detomidine in Thoroughbred horses are different when the drug is given during recuperation from a brief period of maximal exercise compared to administration at rest. Methods: Six Thoroughbred horses were preconditioned by exercising them on a treadmill. Each horse ran a simulated race at a treadmill speed that caused it to exercise at 120% of its maximal oxygen consumption. One minute after the end of exercise, horses were treated with detomidine. Each horse was treated with the same dose of detomidine on a second occasion a minimum of 14 days later while standing in a stocks. Samples of heparinised blood were obtained at various time points on both occasions. Plasma detomidine concentrations were determined by liquid chromatographymass spectrometry. The plasma concentration vs. time data were analysed by nonlinear regression analysis. Results: Median back‐extrapolated time zero plasma concentration was significantly lower and median plasma half‐life and median mean residence time were significantly longer when detomidine was administered after exercise compared to administration at rest. Median volume of distribution was significantly higher after exercise but median plasma clearance was not different between the 2 administrations. Conclusions and potential relevance: Detomidine i.v. is more widely distributed when administered to horses immediately after exercise compared to administration at rest resulting in lower peak plasma concentrations and a slower rate of elimination. The dose requirement to produce an equivalent effect may be higher in horses after exercise than in resting horses and less frequent subsequent doses may be required to produce a sustained effect.     

Standardized exercise test and daily heart rate responses of thoroughbreds undergoing conventional race training and detraining

Ten healthy sedentary male Thoroughbreds with previous race training experience were studied for 14 weeks. Horses were trained for 9 weeks, using a program designed after those used commonly in the United States. Horses were trained conventionally by slow trotting (250 m/min) for 2 weeks and galloping (390 to 450 m/min) for 4 weeks, followed by 3 weeks of galloping (440 to 480 m/min) and intermittent sprinting exercises (breezes) at distances between 600 and 1,000 m (900 to 950 m/min). The horses were then pasture rested for 5 weeks. A standardized exercise test (SET) involving an 800-m gallop at 800 m/min was administered before and after the 9-week training period and after the 5-week detraining period. Heart rate (HR) was monitored during exercise and at standardized intervals after exercise for 60 minutes. Venous blood for determination of plasma lactate concentration was obtained at 5 minutes after exercise. Heart rate was monitored daily at rest, during exercise, and through the first 60 minutes of recovery. Venous plasma samples (for lactate determination) were obtained 5 minutes after the sprinting exercises. Horses were observed daily before exercise for signs of lameness and were not allowed to train if lame. Differences after 9 weeks' training were seen in the SET recovery HR at 0.5 through 5 minutes after exercise (P less than 0.05 to P less than 0.01). Differences after detraining were seen in the SET recovery HR at 40 and 60 minutes after exercise (P less than 0.05 to P less than 0.01). Neither training nor detraining resulted in differences in plasma lactate concentration after the SET gallop.(ABSTRACT TRUNCATED AT 250 WORDS)     

The efficacy of dantrolene sodium in controlling exertional rhabdomyolysis in the Thoroughbred racehorse

REASONS FOR PERFORMING STUDY: Dantrolene sodium (Dantrium) has been used extensively for the treatment of myopathies in man and anecdotal evidence suggests it is of clinical benefit in the control of exercise-induced rhabdomyolysis (ER) in racehorses, although data to support this are currently lacking. OBJECTIVES: To investigate the efficacy of oral dantrolene sodium in controlling ER in a randomised, double-blind, placebo-controlled crossover trial involving 77 Thoroughbred racehorses in Newmarket, UK. METHODS: Horses were treated on 2 occasions 1 week apart, with treatment days coinciding with a return to exercise following 2 days box rest on each occasion. For the first treatment, each horse was randomly selected to receive either 800 mg dantrolene sodium or a colour-matched placebo administered orally 1 h before exercise. This was followed by crossover to the other treatment on the second occasion, with each horse thereby acting as its own control. Degree of ER was assessed using rising serum creatine kinase (CK) levels, by subtracting pre-exercise blood CK levels from those measured in 6 h post exercise blood samples. For each horse, the difference in change between pre- and post exercise CK values between placebo and dantrolene treatments was calculated, with positive values indicating a greater rise with placebo than with dantrolene sodium treatment. RESULTS: The overall mean difference for all horses was +104.8 iu/l and the null hypothesis, that there was no true difference in non-normally distributed post exercise rises in CK values between placebo and dantrolene treatments, was rejected (P = 0.0013) using the nonparametric Wilcoxon signed rank test. Additionally, no horses given dantrolene sodium showed clinical signs of ER, whereas 3 horses given the placebo developed ER following exercise. The incidence of ER in the study was 4% (3/77). CONCLUSIONS: The results confirmed that oral administration of dantrolene sodium, 1 h before exercise, had a statistically significant effect on reducing the difference between pre- and post exercise plasma CK levels compared with a placebo in the same animals, and preventing clinical ER in susceptible individuals. POTENTIAL RELEVANCE: This study suggested that dantrolene sodium is of use in controlling ER in the Thoroughbred racehorse. Further investigation into pre- and post exercise myoplasmic calcium levels and the repeat of the study late in the season when horses receive a much higher energy ration and more strenuous exercise would appear to be warranted.     

Cardiac output determination by use of lithium dilution during exercise in horses

OBJECTIVE: To compare cardiac output (CO) obtained by the lithium dilution method (LiDCO) with CO calculated from the Fick principle (FickCO), in horses maximally exercising on a high-speed treadmill. ANIMALS: 13 Thoroughbreds. PROCEDURES: In part 1 of the study, 5 horses performed a warm-up (walk, trot, and canter) and exercise test (walk, trot, canter, and gallop [90% to 100% maximum oxygen consumption [{[Formula: see text]O(2)max}]) with measurements of LiDCO and FickCO obtained simultaneously after 60 seconds at each exercise level, for a total of 7 measurements. In part 2 of the study, 8 horses performed a warm-up (walk, trot, and canter) followed by an exercise test (walk and gallop [90% to 100% [Formula: see text]O(2)max], repeated twice). Measurements of LiDCO and FickCO were obtained 60 seconds into the first walk and each gallop of the exercise tests, for a total of 3 measurements. RESULTS: Cardiac output increased significantly with increasing speeds by use of both methods. In part 1, lithium dilution significantly overestimated CO, compared with the Fick principle, during the exercise test (as both injection number and exercise intensity increased). Mean +/- SD bias was 246 +/- 264 mL of blood/min/kg in part 1 and 67 +/- 100mL of blood/kg/min in part 2. Three injections of lithium (part 2) did not result in the same degree of overestimation of LiDCO that was observed with 7 injections (part 1). CONCLUSIONS AND CLINICAL RELEVANCE: Lithium dilution may be an acceptable substitute for the Fick principle as a means to measure CO in maximally exercising client-owned horses.     

Palmar/Plantar Process Fractures of the Proximal Phalanx In 15 Horses

Fifteen fractures of the palmar or plantar process of the proximal phalanx in 15 horses are described. Ten were articular and five were nonarticular. Two modes of therapy were used depending on the location of the fracture. Nonarticular fractures were treated with stall rest or reduction in exercise, and articular fractures were treated with either surgical removal or internal fixation of the fragment. All horses that were operated on were sound within 6 months after surgery. Follow-up information was obtained on all horses through client questionnaire and race records in the racing breeds (Standardbred and Thoroughbred) and client questionnaire alone is the nonracing breeds (Quarterhorse and Arabian). Fourteen horses returned to an equal or better level of performance than before injury; one horse returned to a lower level of performance.