Effect of chronic clenbuterol administration and exercise training on immune function in horses

Effects of longitudinal exercise training and acute intensive exercise (simulated race test) on immune function have not been reported in horses. Clenbuterol, a beta2-adrenergic agonist, is used to manage inflammatory airway disease in horses. This study investigated the interaction of 8 wk of exercise training with or without 12 wk of clenbuterol administration in horses. Twenty-three untrained standardbred mares (10 +/- 3 yr, Mean +/- SE) were used and divided into four experimental groups. Horses given clenbuterol plus exercise (CLENEX; n = 6) and clenbuterol alone (CLEN; n = 6) received 2.4 microg/kg BW of clenbuterol twice daily (in an average volume of 20 mL) on a schedule of 5 d on and 2 d off for 12 wk. The CLENEX group was also aerobically trained 3 d/wk. Mares given exercise alone (EX; n = 5) were aerobically trained for 3 d/wk, and the control group (CON; n = 6) remained sedentary. Both EX and CON horses were administered similar volumes (approximately 20 mL) of molasses twice daily. A simulated race test (SRT) resulted in an elevation in lymphocyte number postexercise (P < 0.05). There was no significant difference after acute exercise in either monocyte or granulocyte number. Acute exercise resulted in a decrease (P < 0.05) in the percentage of CD4+ and an increase (P < 0.05) in the percentage of CD8+ cells. The SRT resulted in a decreased lymphoproliferative response to pokeweed mitogen (P < 0.05). A SRT had no effect on antibody production in response to equine influenza vaccine. The EX group demonstrated greater cortisol concentrations at rest and at all other time points postexercise after completing the training regimen compared with CLENEX horses (P < 0.05). Preexercise (SRT) peripheral blood monocyte number was lower in CLENEX horses than in other treatment groups (P < 0.05). Clenbuterol and exercise training did not significantly affect post-SRT changes in leukocyte numbers. Exercise training resulted in a decrease (P < 0.05) in the percentage of CD8+ cells post-SRT compared with other groups, but the percentage of CD4+ cells was not altered by either clenbuterol or exercise conditioning. Lymphocyte proliferative response was not affected by clenbuterol or exercise treatment. Horses demonstrated responses to bouts of acute exercise as noted with other species, namely humans and rodents.     

Gait and speed as exercise components of risk factors associated with onset of fatigue injury of the third metacarpal bone in 2-year-old Thoroughbred racehorses

OBJECTIVE: To determine the degree to which components of the training program of 2-year-old Thoroughbred racehorses influence their susceptibility to fatigue injury of the third metacarpal bone (bucked shins). ANIMALS: 226 two-year-old Thoroughbred racehorses. PROCEDURE: Daily training information and health reports on 2-year-old Thoroughbreds were compiled from records provided from 5 commercial stables. For each horse, data (exercise variables) were collected that comprised distance jogged (approx speed of 5 m/s), galloped (approx 11 m/s), and breezed (approx 15 to 16 m/s) until a single instance of bucked shins was reported. Data were coded for analysis using cross-tabulation, graphic, and survival techniques. RESULTS: Of 226 horses, 56 had bucked shins, 9 completed the observation period without bucked shins, and 161 were lost to follow-up. Distinct training strategies were used at stables resulting in significantly different survival profiles among stables. Mean (+/- SD) allocation of exercise to breezing was 0.15 +/- 0.13 miles/wk (maximum, 0.64 miles/wk), to galloping was 4.47 +/- 1.52 miles/wk (maximum, 9.56 miles/wk), and to jogging was 2.34 +/- 1.70 miles/wk (maximum, 8.53 miles/wk). Survival (ie, lack of bucked shins during 1 year of monitoring) was found to be significantly reduced by exercise allocation to breezing, significantly increased by exercise allocation to galloping, and uninfluenced by exercise allocation to jogging. The log of the hazard ratio was reduced by 4.2 +/- 1.5/mile breezed and increased by 0.3 +/- 0.1/mile galloped. CONCLUSIONS AND CLINICAL RELEVANCE: Relationships between different gaits and speeds in the training regimen influence the incidence of bucked shins. To reduce the incidence of bucked shins, trainers should consider allocating more training effort to regular short-distance breezing and less to long-distance galloping.     

The effect of dietary fish oil supplementation on exercising horses

Ten horses of Thoroughbred or Standardbred breeding were used to study the effects of dietary fish oil supplementation on the metabolic response to a high-intensity incremental exercise test. Horses were assigned to either a fish oil (n = 6) or corn oil (n = 4) treatment. The fish oil (Omega Protein, Hammond, LA) contained 10.6% eicosapentaenoic acid and 8% docosahexaenoic acid. Each horse received timothy hay and a textured concentrate at a rate necessary to meet its energy needs. The supplemental oil was top-dressed on the concentrate daily at a rate of 324 mg/kg BW. Horses received their assigned diet for 63 d, during which time they were exercised 5 d/wk in a round pen or on a treadmill. During wk 1, horses exercised for 10 min at a trot. After wk 1, exercise time and intensity were increased so that at wk 5, exercise time in the round pen increased to 30 min (10 min of cantering and 20 min of trotting) per day. Starting at wk 6, horses were exercised 3 d/wk in the round pen for 30 min and 2 d/wk on a treadmill for 20 min. After 63 d, all horses performed an exercise test consisting of a 5-min warm-up at 1.9 m/s, 0% grade, followed by a step test on a 10% grade at incremental speeds of 2 to 8 m/s. Blood samples were taken throughout exercise. During exercise, horses receiving fish oil had a lower heart rate (treatment x time interaction; P < 0.05) and tended to have lower packed cell volume (treatment effect; P = 0.087). Plasma lactate concentrations were not affected by treatment. Plasma glucose concentrations were not different between groups during exercise but were lower (treatment x time interaction; P < 0.01) for the fish oil group during recovery. Serum insulin tended to be lower in fish oil horses throughout exercise (treatment effect; P = 0.064). There was a tendency for glucose:insulin ratios to be higher for fish oil-treated horses throughout exercise (treatment effect; P = 0.065). Plasma FFA were lower (treatment x time interaction; P < 0.01) in horses receiving fish oil than in horses receiving corn oil during the initial stages of the exercise test. Serum glycerol concentrations also were lower in fish oil-treated horses (P < 0.05). Serum cholesterol concentrations were lower in horses receiving fish oil (treatment effect; P < 0.05), but serum triglycerides were not affected by treatment (P = 0.55). These data suggest that addition of fish oil to the diet alters exercise metabolism in conditioned horses.     

Nutritional management of horses competing in 160 km races

A survey was taken of dietary management and training schedules of 54 horses competing in two 160 km endurance races. A total of 52 owners, representing 54 horses, responded to a questionnaire distributed prior to the races. Diet and training schedules were compared between horses that successfully completed the races and those that were eliminated for metabolic reasons. Horses that completed the races were 11.5 +/- 4 years old, weighed 429 +/- 4.5 kg and were ridden 61 +/- 32 km a week when training. Feed intake was reported as "free choice hay or pasture" by 34 of the respondents. Dry matter (DM) hay intake in these horses was estimated to be 3% body weight (kg) minus the kg DM of grain fed, assuming a maximum intake. They were fed 12.3 +/- 2.3 kg feed per day consisting of 10 +/- 2.3 kg hay and 2.3 +/- 1.4 kg of grain. Most had free access to salt and were fed 1 +/- 1 vitamin/mineral supplement per day. Based on Nutritional Research Council (NRC) values for nutrient content of the reported feeds, diets contained 60 +/- 5% total digestible nutrients (TDN), 12 +/- 2% crude protein, 27 +/- 4% crude fiber, 0.72 +/- 0.4% calcium and 0.29 +/- 0.06% phosphorus. Maximum caloric intake was estimated to be 31.9 Mcal per day. Ratios of nutrients fed per kilometer trained were: kg TDN/km = .14 +/- .08, kg crude protein/km trained = .03 +/- .02, and kg crude fiber/km trained = .06 +/- .04.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of initiation of exercise training in young horses on vitamin K status

Twelve Quarter Horses, 18 to 24 mo of age and having an average body weight of 460+/-12 kg, were randomly assigned to one of two exercise treatments (control and exercise) to study the effect of initiation of exercise training in young horses on vitamin K status. The control treatment consisted of hand-walking the horses 7 min/d and 5 d/wk for 180 d. Exercise consisted of the following treadmill exercise regimen: 2 min at 4.5 to 5.4 m/s, 3 min at 13.4 to 14.3 m/s, and 2 min at 4.5 to 5.4 m/s on 5 d/wk for 180 d. Both groups were allowed free access to brome grass hay (273 mg of phylloquinone/100 g) individually. Additionally, the exercise group was fed .45 kg of a grain-mix concentrate (40 mg of phylloquinone/100 g) on the days they were exercised. Jugular venous blood samples were collected at d 0, 30, 60, 90, 120, 150, and 180. Blood samples were analyzed for total serum osteocalcin and vitamin K status via the hydroxyapatite binding capacity of serum osteocalcin calculated as follows: Hydroxyapatite binding capacity of serum osteocalcin = [(total serum osteocalcin - serum osteocalcin following extraction of serum with hydroxyapatite)/total serum osteocalcin] x 100. All horses were killed with an overdose of sodium pentobarbital on d 180. Computed tomographic osteoabsorptiometry was used to measure relative bone density distribution on the surface of the distal radial carpal bone, proximal third carpal bone, and the distal third metacarpal condyle. Relative bone density distribution was measured in Hounsfield units and categorized as low-, medium-, and high-density bone corresponding to 800 to 1,199, 1,200 to 1,299, and 1,300 to 3,000 Hounsfield units, respectively. Carpal and metacarpophalangeal joints were assigned a score of 0 (normal) to 3 (severe) that reflected the presence and severity of joint lesions. Hydroxyapatite binding capacity of serum osteocalcin and serum osteocalcin were unchanged over the 180-d period in both groups. Exercised horses had a higher percentage of high density bone (P < .01) and a lower percentage of low density bone (P < .01) on the surface of the third metacarpal condyle and a higher cumulative gross lesion score (P < .01) in the metacarpophalangeal joint than controls. There were no differences between treatments in relative bone density distribution in the carpal bones, or cumulative gross lesion score of the carpal joints. No significant correlation was present between the serum measures, osteocalcin and hydroxyapatite binding capacity of serum osteocalcin, and the bone measures, relative bone density distribution and joint gross lesion score.     

Endothelin response during and after exercise in horses

The objective of the present study was to measure plasma endothelin-1 (ET-1) at rest and during exercise in the horse. Six healthy, Standardbred and Thoroughbred mares (5.3+/-0.8 years; 445.2+/-13.1 kg) which were unfit, but otherwise accustomed to running on the treadmill, were used in the study. Plasma ET-1 concentrations were measured using a commercially available radioimmunoassay kit. Horses performed three trials: a standing control (CON) trial where blood was collected from the jugular vein every minute for 5 min; a graded exercise test (GXT) where blood samples were collected at the end of each 1 min step of an incremental exercise test; and a 15 min submaximal (60% VO(2max)) steady-state exercise test (SST) where blood samples were collected 1 min before, immediately after, and at 2 min, 10 min and 20 min post-exercise. Plasma ET-1 concentration did not change (P>0.05) during the CON trial where it averaged 0.18+/- 0.03 pg/mL (mean+/-SE). Surprisingly, plasma ET-1 concentration did not change during the GXT trial where it averaged 0.20+/-0.03 pg/mL. There were no differences between the mean concentrations obtained in either trial (P>0.05). Plasma ET-1 concentrations were, however, significantly elevated (P<0.05) immediately following exercise and at 2 min post-exercise in the SST. Post-exercise plasma ET-1 concentrations returned to baseline (P>0.05) by 10 min of recovery. Together, these data may suggest that ET-1 concentrations are altered in response to an exercise challenge.     

Salivary Cortisol Concentration in Exercised Thoroughbred Horses

Both physical activity and stress result in an increase in plasma cortisol level. The measurement of cortisol in plasma requires taking blood samples, which is stressful itself. Therefore, the aim of this study was to evaluate the use of saliva sampling for the determination of cortisol concentrations, indicating the intensity of exercise in horses during race training. Twelve Thoroughbred horses aged 2-3 years were examined during their speed training sessions. The horses galloped on the 1,200-m sand track at a speed of 14.4-15.3 m/s. Three saliva samples and three blood samples were collected from each horse. Both types of samples were taken when the horse was at rest, immediately after returning from the track and 30 minutes after the end of exercise. Blood lactic acid (LA) concentration was determined using the enzymatic cuvette test. The concentrations of cortisol in saliva and plasma samples were measured by enzyme immunoassay methods. Statistically significant correlations were found between salivary cortisol level determined 30 minutes after the end of exercise and blood LA concentration obtained immediately after exercise (P = .003) and between salivary and plasma cortisol levels measured 30 minutes after the end of training session (P = .015). The measurement of cortisol concentration in saliva samples taken from race horses 30 minutes after the end of exercise can be recommended for use in practice under field conditions to estimate the level of relative intensity of exercise in race horses.     

Plasma cortisol and ACTH concentrations in the warmblood horse in response to a standardized treadmill exercise test as physiological markers for evaluation of training status

Reliable physiological markers for performance evaluation in sport horses are missing. To determine the diagnostic value of plasma ACTH and cortisol measurements in the warmblood horse, 10 initially 3-yr-old geldings of the Hannovarian breed were either exposed to a training schedule or served as controls. During experimental Phase 1, horses were group-housed, and half of the horses were trained for 20 wk on a high-speed treadmill. During Phase 2, groups were switched and one group was trained for 10 wk as during Phase 1, whereas the control group was confined to boxes. During Phase 3 horses were initially schooled for riding. Thereafter, all horses were regularly schooled for dressage and jumping, and half of the horses received an additional endurance training for 24 wk. During all phases horses were exposed at regular intervals to various standardized treadmill exercise tests. During and after the tests frequent blood samples were taken from an indwelling jugular catheter for determination of ACTH and cortisol. Treadmill exercise increased both hormones. Maximum ACTH concentrations were recorded at the end of exercise, and maximum cortisol levels were recorded 20 to 30 min later. Except for one test there were no differences in ACTH levels between trained horses and controls. There was no significant effect of training on the cortisol response (net increase) to treadmill exercise in any of the tests during Phase 1. During Phase 2 higher cortisol responses were recorded in controls than in trained horses (P < .05) after 10 wk of training (controls confined to boxes). During Phase 3 plasma cortisol responses were also higher in controls than in trained horses (P < .05 after 6, 18, and 24, P < or = .07 after 12 wk of training) when the inclination of the treadmill was 5%, but not at 3%. There was no overlap in net cortisol responses at 30 min between trained and untrained horses. An ACTH application after 24 wk of training resulted in higher cortisol responses in controls than in trained horses (P < or = .05), without any overlap between the groups at 30 min after ACTH. Plasma cortisol responses to either treadmill exercise or ACTH injection may be a reliable physiological marker for performance evaluation. Prerequisites are sufficient differences in training status and sufficient intensity of exercise test conditions.     

Arterial blood PO2 and PCO2 in horses during early halothane-oxygen anaesthesia

Arterial blood was collected from 25 clinically normal horses immediately before and serially throughout the first hour of halothane oxygen anaesthesia. Blood was analysed for oxygen and carbon dioxide partial pressure (PaO2, PaCO2). Measurements of inspired oxygen concentration during anaesthesia permitted direct correlation with blood gases. Horses were divided arbitrarily into two groups based on their age: two to seven years, n = 15; over seven years, n = 10. Average (+/- sd) PaO2 and PaCO2 was 14.1 +/- 1.5 kPa (106 +/- 11 mmHg) and 5.9 +/- 0.6 kPa (44.4 +/- 4.4 mmHg) respectively in conscious, young horses and 14.0 +/- 0.7 and 5.8 +/- 0.5 kPa (105 +/- 5 and 43.3 +/- 3.8 mmHg) respectively in conscious older horses. Arterial oxygen tension decreased to 9.3 +/- 1.0 and 8.5 +/- 1.4 kPa (69.6 +/- 7.8 and 63.7 +/- 10.4 mmHg) in young and older air breathing horses respectively immediately following intravenous anaesthetic induction, recumbency and orotracheal intubation. At this time, PaCO2 was 6.5 +/- 0.5 and 6.0 +/- 0.7 kPa (48.7 +/- 3.5 and 45.1 +/- 4.9 mmHg) respectively. By 30 mins after the start of halothane in oxygen (6 litres/min) anaesthesia PaO2 increased to a maximum in both study groups. Arterial PCO2 increased steadily during anaesthesia and 60 mins after induction PaCO2 was 10.5 +/- 2.4 kPa (78.5 +/- 17.8 mmHg) in the younger horses and 9.2 +/- 1.6 kPa (68.8 +/- 11.8 mmHg) in the older horses. During inhalation anaesthesia PaO2 tended to be greater at comparable time periods in the younger horses despite a slightly greater degree of hypoventilation.     

Plasma ionized calcium and parathyroid hormone concentrations in horses after endurance rides

OBJECTIVE: To evaluate changes in plasma ionized calcium (Ca2+) and parathyroid hormone (PTH) concentrations in horses competing in endurance rides. DESIGN: Longitudinal clinical study. ANIMALS: 28 horses. PROCEDURE: Venous blood samples were obtained from horses before and after racing 80 km. Plasma pH and concentrations of Ca2+, PTH, inorganic phosphorus, albumin, lactate, and magnesium were measured. RESULTS: Overall, a significant decrease in mean (+/- SD) plasma Ca2+ concentration (from 6.44 +/- 0.42 to 5.64 +/- 0.42 mg/dl) and a significant increase in plasma PTH concentration (from 49.9 +/- 30.1 to 148.1 +/- 183.0 pg/ml) were found after exercise. Exercise also resulted in significant increases in plasma inorganic phosphorus, albumin, and lactate concentrations. No changes in plasma magnesium concentration or pH were detected after exercise. Plasma PTH concentration was not increased after exercise in 8 horses; in these horses, plasma PTH concentration decreased from 58.2 +/- 26.3 to 27.4 +/- 22.4 pg/ml, although plasma Ca2+ concentration was also decreased. CONCLUSIONS AND CLINICAL RELEVANCE: Plasma Ca2+ concentration was decreased after racing for 80 km, compared with values obtained before racing. In most horses, an increase in plasma PTH concentration that was commensurate with the decrease in plasma Ca2+ was detected; however, some horses had decreased plasma PTH concentrations.     

Comparison of yearling, two-year-old and adult Thoroughbreds using a standardised exercise test

The purpose of this study was to compare exercise measurements in yearling, two-year-old and adult Thoroughbreds using a standardised treadmill incremental exercise test. Peak oxygen consumption (VO2 peak: 128.0 +/- 2.1, 140.0 +/- 2.1, 163.7 +/- 3.4; ml/kg/min +/- se, P less than 0.05), peak packed cell volume (PCV peak: 0.50 +/- 0.01, 0.58 +/- 0.01, 0.64 +/- 0.01 litres/litre +/- se, P less than 0.05) and the maximum number of steps completed in the exercise test (STEPmax: 7.7 +/- 0.1, 8.1 +/- 0.1, 8.6 +/- 0.1; steps +/- se, P less than 0.05) increased with age and degree of physical activity. Peak venous lactate concentration (LACpeak: 21.3 +/- 1.5, 19.5 +/- 1.7, 14.4 +/- 1.7; mmol/litre +/- se, P less than 0.05) and peak respiratory exchange ratio (Rpeak) were significantly higher in both groups of younger horses compared to the adult racehorses. Peak heart rate (HRpeak: 230 +/- 2, 231 +/- 3, 229 +/- 3; beats/min +/- se) did not change with age or training. The rate of change of VO2 between steps in the exercise test (VO2trans) was significantly lower in the adult racehorses at the highest exercise intensities. The slopes of the linear approximation between R (LinR bx), the natural log transformation of venous lactate concentration (LogLAC bx), and heart rate (HR bx) with velocity were significantly lower in the trained adult racehorses. The slope of venous lactate concentration normalised to per cent VO2peak (LogLAC per cent bx) was significantly lower and R breakpoint (R brkpt) normalised to per cent VO2peak was significantly higher in the trained adult racehorses. There was a more rapid decrease in venous lactate and a more rapid return to initial R values in the adult horses relative to the younger, untrained horses. No significant age or training effects were found in the remainder of the post exercise measurements. These results indicate that aerobic power and exercise capacity increased with age and training. Anaerobic power was already well developed even at a young age.     

Metabolic responses to oral tryptophan supplementation before exercise in horses

This study was conducted to evaluate the effects of oral tryptophan (Trp) supplementation on exercise capacity and metabolic responses in horses. Three horses had to perform an exercise test: a 15-min warm-up followed by a 60-min walk (1.7 m/s, W1), a 10-min trot (3.1 m/s, T1), a second 60-min walk (1.7 m/s, W2), a second 10-min trot (3.1 m/s, T2) and a final 30-min walk (1.7 m/s, W3) until the horses were unwilling to continue. The horses exercised on a treadmill at a 6% incline and with a constant draught load of 40 kg (0.44 kN). Two hours before exercise horses were given 50 g Trp (9.8-10.7 g Trp/100 kg BW) by nasogastric tube. A control exercise test was conducted without Trp. During the control test, one horse was able to finish the final 30-min walk (W3), whereas two horses finished W3 after Trp administration. Higher plasma Trp levels after Trp administration did not change significantly during exercise (Trp: start exercise, 524 +/- 41 micromol/l; end exercise 547 +/- 20 micromol/l; control: start exercise, 70 +/- 10 micromol/l; end exercise, 58 +/- 21 micromol/l). After Trp supplementation, blood lactate concentrations were significantly lower after the first and second trotting periods. Free fatty acids in plasma increased during exercise without any treatment-related differences. Although experimental plasma Trp levels were seven times higher than the control levels, Trp supplementation had no effect on exercise performance and metabolic responses to draught load exercise.     

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.     

Amino acid supplementation improves muscle mass in aged and young horses

The objective of the study was to evaluate the effect of supplementary AA on the ability to support muscle mass in aging horses. Sixteen horses of light horse type were used in a 2 x 2 factorial arrangement of treatments with two age groups [< or = 10 yr (average = 9.1 +/- 0.29 yr) and > or = 20 yr (average = 22.4 +/- 0.87 yr)] and two diet groups [no supplementation (N) or supplementary lysine and threonine (S; 20.0 and 15 g/d, respectively)]. Horses were fed the diets for 14 wk and received regular light exercise throughout the study. Body weight, BCS, and venous blood samples were taken every 2 wk. Plasma was analyzed for total protein, albumin, creatinine, urea N (PUN), and an AA profile, including 3-methyl histidine (3MH) and sulfur AA. Photographs of the horses taken at the start and at the end of the experiment were used to assign a subjective muscle mass score from 1 to 5 (1 = lowest to 5 = highest). There was no difference in BW caused by diet; however, the S-group horses tended (P = 0.064) to gain more weight (6.91 +/- 2.3 kg), and in fact, the N-group horses lost weight (- 11.76 +/- 5.2 kg) during the experiment. Repeated measures analysis revealed that BCS was lower for the aged vs. the young horses (P = 0.001) as well as for the S- vs. the N-group horses (P = 0.026). Subjective muscle mass scores were not different at the start of the experiment but were greater (P = 0.047) for the S-group horses (3.77 +/- 0.13) at the end of the experiment compared with the N-group horses (3.28 +/- 0.14). Plasma creatinine was greater (P = 0.032), and PUN was lower (P = 0.027), for S-group horses compared with N-group horses. Initial 3MH concentrations were not different; however, at the end of the experiment, 3MH was lower for the S-group horses (P = 0.016) compared with the N-group horses. Plasma lysine and threonine concentrations were greater for S-group horses at the end of the experiment than for N-group horses (P = 0.023 and 0.009, respectively). Both 3MH and PUN concentrations were negatively correlated to lysine (R2 = 0.57 and 0.65, respectively) and threonine intake (R2 = 0.56 and 0.60, respectively) at the end of the study. These data suggest that horses receiving supplementary AA were able to maintain muscle mass better than those without supplementation, regardless of age, as evidenced by the improvement in muscle mass scores, lower BCS with no difference in BW, greater creatinine, and lower 3MH and PUN concentrations in the S-group horses.     

Pharmacokinetics of marbofloxacin in mature horses after single intravenous and intramuscular administration

The pharmacokinetic behaviour of marbofloxacin, a new fluoroquinolone antimicrobial agent developed exclusively for veterinary use, was studied in mature horses (n = 5) after single-dose i.v. and i.m. administrations of 2 mg/kg bwt. Drug concentrations in plasma were determined by high performance liquid chromatography (HPLC) and data obtained were subjected to compartmental and noncompartmental kinetic analysis. This compound presents a relatively high volume of distribution (V(SS) = 1.17 +/- 0.18 l/kg), which suggests good tissue penetration, and a total body clearance (Cl) of 0.19 +/- 0.042 l/kgh, which is related to a long elimination half-life (t(1/2beta) = 4.74 +/- 0.8 h and 5.47 +/- 1.33 h i.v. and i.m. respectively). Marbofloxacin was rapidly absorbed after i.m. administration (MAT = 33.8 +/- 14.2 min) and presented high bioavailability (F = 87.9 +/- 6.0%). Pharmacokinetic parameters are not significantly different between both routes of administration (P>0.05). After marbofloxacin i.m. administration, no adverse reactions at the site of injection were observed. Serum CK activity levels 12 h after administration increased over 8-fold (range 3-15) compared with pre-injection levels, but this activity decreased to 3-fold during the 24 h follow-up period. Based on the value of surrogate markers to predict clinical success, Cmax/MIC ratio or AUC/MIC ratio, single daily marbofloxacin dose of 2 mg/kg bwt may not be effective in treating infections in horses caused by pathogens with an MIC > or = 0.25 microg/ml. However, if we use a classical antimicrobial efficacy criteria, marbofloxacin can reach a high plasma peak concentration and maintain concentrations higher than MICs determined for marbofloxacin against most gram-negative veterinary pathogens throughout the administration period. Taking into account the fact that fluoroquinolones are considered to have a concentration-dependent effect and a long postantibiotic effect against gram-negative bacteria, a dose of 2 mg/kg bwt every 24 h could be adequate for marbofloxacin in horses.     

Ingestion of starch-rich meals after exercise increases glucose kinetics but fails to enhance muscle glycogen replenishment in horses

Fatiguing exercise substantially decreases muscle glycogen concentration in horses, impairing athletic performance in subsequent exercise bouts. Our objective was to determine the effect of ingestion of starch-rich meals after exercise on whole body glucose kinetics and muscle glycogen replenishment. In a randomized, cross-over study seven horses with exercise-induced muscle glycogen depletion were either not fed for 8 h, fed half of the daily energy requirements ( approximately 15 Mcal DE) as hay, or fed an isocaloric amount of corn 15 min and 4 h after exercise. Starch-rich meals fed after exercise, when compared to feed withholding, resulted in mild to moderate hyperglycemia (5.7+/-0.3 vs. 4.7+/-0.3 mM, P<0.01) and hyperinsulinemia (79.9+/-9.3 vs. 39.0+/-1.9 pM, P<0.001), 3-fold greater whole body glucose kinetics (15.5+/-1.4 vs. 5.3+/-0.4 micromol kg(-1)min(-1), P<0.05), but these only minimally enhanced muscle glycogen replenishment (171+/-19 vs. 170+/-56 and 260+/-45 vs. 294+/-29 mmol/kg dry weight immediately and 24 h after exercise, P>0.05). It is concluded that after substantial exercise-induced muscle glycogen depletion, feeding status only minimally affects net muscle glycogen concentrations after exercise, despite marked differences in soluble carbohydrate ingestion and availability of glucose to skeletal muscle.     

Pulmonary wedge pressure and heart frequency measurements during standardized treadmill exercise for extension of left atrial function diagnosis in warmblood horses

In 12 healthy warmblood horses (six trained and six untrained) the pulmonary wedge pressure and heart frequency was measured at rest and during a standardised exercise test on a treadmill. The mean pulmonary wedge pressure at rest was 14.53 +/- 2.36 mmHg. There was no significant difference in pulmonary wedge pressure either at rest or during exercise between trained and untrained horses. During walking (1.8 m/s) the mean pulmonary wedge pressure was 19.62 +/- 4.03 mmHg, during trotting (4 und 5 m/s) it was between 22.38 +/- 3.92 mmHg and 25.28 +/- 3.7 mmHg. During canter (6 m/s) and gallop (8 m/s) the mean pulmonary wedge pressure increased to a level of 25.54 +/- 4.3 mmHg and 31.86 +/- 4.29 mmHg. There was a significant increase in pulmonary wedge pressure with each incremental step of the standardised treadmill test. Concerning mean heart frequency a highly significant increase could be observed at the beginning and at the end (treadmill speed of 7 and 8 m/s) of the standardised exercise test. At higher intensity of the exercise test (7 m/s and 8 m/s) untrained horses showed a significantly increased heart rate compared to trained horses. Neither at rest nor during the different exercise levels a significant correlation factor greater 0.5 between heart frequency and pulmonary wedge pressure could be observed. The increase of heart frequency and pulmonary wedge pressure during exercise showed no correlation. Between left atrial size and pulmonary wedge pressure a statistical weak correlation could be observed up to a treadmill velocity of 6 and 7 m/s.     

Assessment of copper and zinc status of farm horses and training thoroughbreds in south-east Queensland

The copper and zinc concentrations in the blood of stabled thoroughbred horses and in Australian Stock Horses mares at pasture, either late pregnant or lactating were determined by an atomic absorption spectroscopic method. The plasma concentration of the trace elements in these apparently normal horses were generally below the "normal" range. The plasma copper, caeruloplasmin copper, whole blood copper and plasma zinc concentrations in the stabled thoroughbreds were 0.76 +/- 0.19 micrograms/ml (n = 82), 0.56 +/- 0.14 micrograms/ml (n = 83), 0.75 +/- 0.18 micrograms/ml (n = 82) and 0.47 +/- 0.09 micrograms/ml (n = 83) respectively. The plasma copper and zinc concentrations of all the brood mares at pasture (pregnant and lactating) were 0.56 +/- 0.20 micrograms/ml and 0.47 +/- 0.11 micrograms/ml (n = 30). The plasma copper concentration of the pregnant group of mares (0.64 +/- 0.18 micrograms/ml; (n = 14) was greater than that of the lactating mares (0.49 +/- 0.21; (n = 16). Variation in the plasma copper concentration was also identified between stabled and farm horses, between horses of different stables and between horses of different ages. The proportion of plasma copper bound to caeruloplasmin was 73 +/- 11.8%. These low concentrations of copper and zinc in the plasma of apparently normal horses are of clinical significance since recent evidence has indicated that copper deficiency appears to promote the development of skeletal abnormalities in foals. An alternative to the use of a single plasma sample to identify the copper or zinc deficient horse was discussed.     

The effect of interval versus continuous exercise on plasma leptin and ghrelin concentration in young trotters

The effect of interval vs. continuous exercise on plasma leptin and ghrelin concentration in young Standardbred horses was studied. The experiment was conducted on 27 trotters, in the age between 2 and 3 years. They were divided into two groups according to the type of exercise. Blood samples were collected through jugular venipuncture in the following experimental conditions: at rest, immediately after exercise and 30 minutes after the end of the effort. Plasma leptin and ghrelin concentrations were determined using RIA tests. The continuous exercise induced an increase in plasma leptin concentration whereas the interval type of exercise did not influence the level of this hormone (3.47 +/- 0.78 vs. 4.07 +/- 0.94 and 2.31 +/- 0.15 vs. 2.36 +/- 0.21 ng/mL, respectively). The plasma ghrelin concentration measured after the continuous exercise, significantly increased (720 +/- 27.4 vs. 814 +/- 13.8; p < or = 0.05) whereas concentration of this hormone assessed after the interval exercise, significantly dropped (982 +/- 56.5 vs. 842 +/- 35.6 pg/mL; p < or = 0.05). The changes in plasma ghrelin concentration measured after the end of the effort correlated inversely with blood lactic acid concentration. In conclusion, the obtained results showed that medium-intensive type of exercise, such as trot, interval or continuous, slightly affected plasma leptin level but significantly affected plasma ghrelin concentration in young Standardbred trotters.     

Effects of an external nasal strip and frusemide on pulmonary haemorrhage in Thoroughbreds following high-intensity exercise.

The purpose of this study was to examine the effects of an external nasal strip (NS), frusemide (FR) and a combination of the 2 treatments (NS + FR) on exercise-induced pulmonary haemorrhage (EIPH) in Thoroughbred horses. It was hypothesised that both the NS and FR would attenuate EIPH as assessed by red blood cell count in bronchoalveolar lavage fluid. In random order, 8 horses completed each of 4 sprint exercise tests on a treadmill: 1) NS; 2) FR (0.5 mg/kg bwt i.v., 4 h pre-exercise); 3) NS + FR; and 4) control (C; no treatment). After a 5 min warm-up (4.5 m/s), horses completed 2 min running at 120% maximum oxygen consumption (VO2max) with the treadmill set at 3 degrees incline. Mean +/- s.d. running speed was 14.2+/-0.2 m/s. In the FR and NS + FR trials, horses carried weight equal to that lost as a result of frusemide administration. During exercise at 120% Vo2max, oxygen consumption (Vo2) and carbon dioxide production (Vco2) were measured at 15 s intervals. Plasma lactate concentration was measured in samples collected before exercise, at the end of the sprint and after 5 min cool-down at the trot. Thirty minutes after the run, bronchoalveolar lavage (BAL) was performed and the red cell count in the fluid quantified. Vo2 and Vco2 were significantly lower in NS and NS + FR trials than in the C and FR trials at the end of the sprint exercise protocol. However, plasma lactate concentrations did not differ among treatments. Compared with the C trial (61.1+/-30.5 x 10(6) red blood cells/ml BAL fluid), pulmonary haemorrhage was significantly (P<0.05) decreased in both the NS (15.9+/-4.0 x 106 RBC/ml) and FR (12.2+/-5.8 x 10(6) RBC/ml) trials. EIPH in the NS + FR trial (7.9+/-1.0 x 10(6) RBC/ml) was further diminished (P<0.05) compared to the NS trial, but not different from the FR trial. We conclude that both the external nasal strip and frusemide attenuate pulmonary haemorrhage in Thoroughbred horses during high-speed sprint exercise. The external nasal strip appears to lower the metabolic cost of supramaximal exertion in horses. Given the purported ergogenic effects of frusemide, the external nasal strip is a valuable alternative for the attenuation of EIPH.