Effects of flunixin on cardiorespiratory, plasma lactate and stride length responses to intense treadmill exercise in Standardbred trotters.

REASONS FOR PERFORMING STUDY: Since nonsteroidal anti-inflammatory drugs, such as flunixin, on account of their anti-inflammatory and analgesic properties, are used in both racing and equestrian sport horses, the question has been raised as to whether these drugs affect the physiological responses to exercise and thus performance potential. OBJECTIVES: The aims of this investigation were to study the effects of flunixin on cardiorespiratory, metabolic and locomotor parameters in horses during intense treadmill exercise. METHODS: Six Standardbred trotters underwent an incremental treadmill exercise test to fatigue, without drug and then after administration of flunixin meglumine (1.1 mg/kg bwt i.m.). Heart rate (HR), oxygen uptake and stride length were measured and venous blood samples drawn repeatedly during the test. RESULTS: Heart rates were found to be significantly higher at submaximal speeds, while the velocity causing a HR of 200 beats/min was significantly decreased after treatment with flunixin. Maximal HR and plasma lactate concentration 5 min after exercise were unchanged after medication. Flunixin caused higher plasma lactate concentrations at all speeds and the lactate threshold was decreased, compared with baseline values. Oxygen uptake levelled off at the highest velocities and did not change after flunixin treatment. Stride length was increased after treatment, although not at the highest velocities. CONCLUSION: The increased HR and lactate responses to exercise after flunixin treatment indicate that it does influence physiological responses, but does not improve the performance potential of clinically healthy horses. However, the lengthened stride during submaximal exercise after medication could imply undetected subclinical lameness, masked in some of the horses, i.e. they have performed with a longer stride at the cost of a higher heart rate and an increased lactate concentration.

Effect of sodium bicarbonate administration on metabolic responses to maximal exercise.

Administration of bicarbonate has been shown to cause metabolic alkalosis both in man and in horses and is, therefore, thought to increase the buffering capacity of the body and thereby delay the onset of fatigue. However, results regarding the influence of sodium bicarbonate loading on performance both in human athletes and in horses are conflicting. The aim of this study was, therefore, to investigate the metabolic response to a standardised treadmill exercise test to fatigue, in horses given bicarbonate (0.6 g/kg bwt), in comparison to horses given placebo (water). Five Standardbred trotters performed the test on 2 occasions. Venous blood samples were collected before and after administration of test substance, during exercise and during recovery. Muscle biopsy specimens were taken at rest, postexercise and at 15 min of recovery. The increases in pH and concentration of bicarbonate in the blood and the shift seen in base excess showed that the administration of sodium bicarbonate caused metabolic alkalosis. Exercise caused similar decreases in muscle ATP, CP and glycogen and similar increases in muscle IMP, lactate and plasma lactate and uric acid concentrations both in the placebo- and bicarbonate-treated group. The effect upon postexercise muscle and plasma metabolites was similar with both test treatments. Duration of exercise did not change after sodium bicarbonate intake. In conclusion, sodium bicarbonate caused metabolic alkalosis, but did not affect the metabolic response or duration of exercise.

Effects of phlebotomy on haemodynamic characteristics during exercise in standardbred trotters with red cell hypervolaemia.

Five Standardbred trotters with red cell hypervolaemia (RCHV) were compared before and after removal of approximately 22% (36 ml/kg bwt) of the total blood volume in order to evaluate the haemodynamic responses, haemorheological alterations and oxygen transport during exercise to fatigue. Data were recorded during submaximal exercise at 4 different speeds on a treadmill and then during continued running at the highest speed step until fatigue. Oxygen uptake (VO2), pulmonary artery pressure (PAP), systemic artery pressure (SAP), heart rate (HR), haematocrit and haemoglobin concentrations (Hb) were measured. Arteriovenous O2 content difference (C(a-v)O2), pulmonary vascular resistance (PVR) and total systemic resistance (TSR) were calculated. Whole blood and plasma viscosity and erythrocyte aggregation tendency were determined with a rotational viscometer. Endoscopy was performed after exercise. ANOVA was used for statistical analysis. Phlebotomy resulted in a decrease in haematocrit and Hb during the course of exercise. Blood and plasma viscosity were lower and erythrocyte aggregation tendency was higher after phlebotomy. Throughout exercise, including submaximal work and continued running to fatigue, PAP, SAP, PVR, TSR and C(a-v)O2 were lower after phlebotomy. HR was higher after phlebotomy during submaximal exercise. Oxygen delivery and VO2 were lower after phlebotomy in the period from submaximal exercise to fatigue. Run time to fatigue was shorter after phlebotomy. Four horses showed exercise-induced pulmonary haemorrhage (EIPH) before phlebotomy and the degree of bleeding was diminished but not abolished after phlebotomy. The reductions in PVR, TSR, PAP and SAP after phlebotomy were probably a result of reduced blood viscosity. In conclusion, although a 22% reduction in blood volume improved the haemodynamic and haemorheological parameters and the degree of EIPH, it was found that RCHV trotters have to rely on high oxygen delivery to the working muscles for maintenance of maximal performance.

Effect of creatine supplementation on muscle metabolic response to a maximal treadmill exercise test in Standardbred horses.

The aim of the present study was to investigate the effect of creatine (Cr) supplementation on muscle metabolic response in connection with a maximal treadmill exercise test, known to cause a marked anaerobic metabolic response and adenine nucleotide degradation. First, 6 Standardbred trotters performed a standardised maximal exercise test until fatigue (baseline test). The test used was an inclined incremental treadmill test in which the speed was increased by 1 m/s, starting at 7 m/s, every 60 s until the horse could no longer keep pace with the treadmill. After this baseline test, the horses were separated into 2 equal groups. One half received a dose of 25 g creatine monohydrate twice daily, and the other group were given the same dose of lactose (placebo). The supplementation period was 6.5 days, after which the maximal treadmill exercise test was performed again. A washout period of 14 days was allowed before treatments were switched between groups and a new supplementation period started. After this second supplementation period a new maximal exercise test was performed. After supplementation with creatine or placebo, horses were stopped after performing the same number of speed steps and duration of exercise as they had in the baseline test. Blood samples for analysis of plasma lactate, creatine (Cr), creatinine, hypoxanthine, xanthine and uric acid concentrations were collected at rest, during each speed step and during recovery. The total blood volume (TBV) was also determined. Muscle biopsies for analysis of muscle metabolites (adenosine triphosphate [ATP], adenosine diphosphate [ADP], adenosine monophosphate [AMP], inosine monophosphate [IMP], creatine phosphate [CP], lactate [La] and glycogen) were taken at rest, immediately post exercise and after 15 min recovery. The results showed no significant increase in plasma Cr or muscle total creatine concentration (TCr) after supplementation with Cr. At the end of exercise ATP and CP concentrations had decreased and IMP and lactate concentrations increased in muscle in all groups. Plasma lactate concentration increased during exercise and recovery and plasma uric acid concentration increased during recovery in all groups. No influence could be found in TBV after supplementation with creatine. These results show that creatine supplementation in the dosage used in this study had no influence on muscle metabolic response or TBV.

Haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia.

In order to evaluate the haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia (RCHV), 12 trotters with RCHV were compared with 9 normovolaemic (NV) trotters. Haemodynamic data were recorded during exercise at 4 different speeds on a treadmill. Oxygen uptake was determined with an open bias flow system. Pulmonary artery pressure (PAP), systemic artery pressure (SAP), heart rate, packed cell volume (PCV) and plasma lactate and haemoglobin ([Hb]) concentrations were measured. Arteriovenous O2 content difference, cardiac output, stroke volume, pulmonary vascular resistance (PVR) and total systemic resistance (TSR) were calculated. Oxygen uptake, arteriovenous O2 content difference, heart rate, cardiac output, stroke volume, TSR and lactate did not differ between groups. The RCHV horses had significantly higher both mean diastolic and systolic PAP compared to NV horses and this difference increased with higher workload. Further, a higher SAP, PVR, PCV and [Hb] were found in RCHV horses during the course of exercise. Eleven of the RCHV horses, but none of the NV, showed exercise-induced pulmonary haemorrhage on endoscopic examination. The increase in red cell volume, resulting in a high PCV and high total blood volume, is suggested to be an important contributor to both the increased blood pressures in pulmonary and systemic circulation during exercise and to the development of exercise-induced pulmonary haemorrhage in RCHV horses.

Ventilation-perfusion relationships during exercise in standardbred trotters with red cell hypervolaemia.

In order to evaluate the pulmonary gas exchange during exercise in Standardbred trotters with red cell hypervolaemia (RCHV), 12 horses with RCHV were compared with 9 normovolaemic (NV) horses. VO2 and VCO2 were determined with an open bias flow system. Cardiovascular and haemodynamic data were recorded during exercise at 4 different speeds on a treadmill. Pulmonary gas exchange was assessed by conventional blood gas variables (arterial and mixed venous blood gas tensions), and the ventilation-perfusion distribution VA/Q was estimated by the multiple inert gas elimination technique. VA and AaDO2 were calculated. Dispersions of perfusion and ventilation distribution (SDQ, SDV) were determined. HR, RR, Qt, VO2, VA, log SDV, C(a-åv)O2 and lactate did not differ between groups. The degree of hypoxaemia was more pronounced in the RCHV than in the NV (PaO2 = 54 and 59 mmHg; AaDO2 = 41 and 34 mmHg in RCHV and NV, respectively, at highest workload). Further, pH was lower in the RCHV and PaCO2 and VCO2 was significantly higher in the RCHV during the course of exercise (pH = 7.24 and 7.29; PaCO2 = 56 and 51 mmHg; VCO2 = 156 and 135 ml/kg x min in RCHV and NV, respectively, at highest workload). The PaO2 predicted from the VA/Q distribution was higher than actually measured in blood during heavy exercise which may suggest a certain diffusion limitation over the alveolar-capillary membranes in both groups but there was no difference between the 2 groups. The more pronounced hypoxaemia observed in RCHV trotters was mainly caused by increased VA/Q mismatch expressed as a significantly increased log SDQ (0.78 and 0.45 in RCHV and NV, respectively, at highest workload).

Incremental treadmill exercise until onset of fatigue and its relationship to metabolic response and locomotion pattern.

The aim was to study metabolic response and locomotion pattern in Standardbred trotters during incremental treadmill exercise performed by increasing speed by 1 m/s in 1 min steps (start 7 m/s) until the onset of fatigue. The test protocol included determination of oxygen uptake, heart rate (HR), stride length (SL) and stride frequency (SF). Venous blood samples were collected at rest, at the end of each exercise step and after 30 min of recovery. Muscle biopsies were taken at rest and post exercise and muscle temperature was measured after exercise. As horses fatigued at different speed steps (9-11 m/s), variation was seen in running time (180-300 s), oxygen uptake (109-170 ml/kg bwt min), HR (200-225 beats/min), SL (4.4-5.7 m) and SF (116-130 strides/min) at the last speed step. Increased mean plasma lactate concentration (20.5 mmol/l) was seen at onset of fatigue and increased mean uric acid concentration after 30 min of recovery (112.8 mumol/l). After exercise, a decrease was seen in muscle ATP (7.1 mmol/kg d.w.), creatine phosphate (43.9 mmol/kg d.w.) and glycogen (160 mmol/kg d.w.), and an increase was seen in ADP (0.3 mmol/kg d.w.), AMP (0.18 mmol/kg d.w.), IMP (5.8 mmol/kg d.w.) and lactate (100.8 mmol/kg d.w.). At onset of fatigue, muscle temperature varied from 39.9-41.4 degrees C. Running time correlated with SL (r = 0.86), with an increase in IMP (r = 0.79) and AMP (r = 0.70) post exercise and with plasma uric acid concentration (r = 0.74) at 30 min of recovery. SF correlated negatively with the increase in ADP after exercise (r = 0.85). The results of this study indicate that running time during incremental treadmill exercise until the onset of fatigue is related to locomotion pattern and to a marked degree of anaerobic metabolism, especially adenine nucleotide degradation.

Racing performance in red blood cell hypervolaemic standardbred trotters.

The association between red blood cell hypervolaemia (RCHV) and racing performance was examined in 116 Standardbred trotters referred to the clinic during a 5 year period with histories of impaired racing performance. Red cell hypervolaemia was the only significant abnormality detected in a thorough clinical examination, cell volumes ranging 116-178% of the predicted normal values. They were also compared with the performance traits of the contemporary Swedish Standardbred trotter population (n = 58,058). The performance traits were based on earnings per year and start, best annual racing time, % placings 1 to 3, and calculated individual performance indices (PI) published in the Annual Statistics for Swedish Trotting. These parameters were transformed to approach normal distributions. The results indicated that horses developing RCHV tended to have been superior athletes initially compared to the contemporary population average. After 3 to 4 years of racing (at mean age +/- s.d. 5.5 +/- 1.5 years) their racing performance declined rapidly during the year of diagnosis of RCHV. Therefore, both earning and placing traits were reduced and best racing time increased. Further, the PI, well above the population average prior to diagnosis, was reduced significantly. During the 3 year period following diagnosis, a slight improvement in racing performance was noted although it was not restored to previous racing form. It was concluded that RCHV in the Standardbred trotter may denote the end of a successful racing career.

Temporary suppression of cell-mediated immunity in standardbred horses with decreased athletic capacity.

Eighty Standardbred horses, originating from 5 training campuses, with decreased athletic performance in association with symptoms such as intermittent fever and mild pharyngitis were examined. As control animals, 10 horses from a stable with normally performing horses were used. Virus isolation and clinico-chemical and serological tests were performed. Lymphocyte proliferation tests were carried out to evaluate the capacity of the cell-mediated immunity. In addition, a bioassay for equine type I interferon, as a marker for early viral infections, was established. No specific microbe could be linked to these symptoms, but there was a temporary suppression of the cell-mediated immunity, which might be explained by the serological evidence of an EHV-2 and/or rhinovirus infection.

Heart rate and blood lactate responses to submaximal treadmill exercise in the normally performing standardbred trotter--age and sex variations and predictability from the total red blood cell volume.

The purposes of this study were to elucidate the influences of age and sex on the heart rate (HR, bpm) and blood lactate (LA, mmol/l) related exercise tolerance parameters V2000 (tread ill velocity at HR 200), VLA4 (velocity at LA 4), W200 (power output at V2000), and WLA4 (power output at VLA4), and to establish reference values for these in normally performing Standardbred trotting race horses. A further aim was to improve the predictability of individual normal values by correlating them with the total red blood cell volume (CV) alone or in combination with the blood lactate response at V200 (LA200). In total 205 horses were included in the study. According to their owners and/or trainers they were all performing satisfactorily (in racing or training) for shortly impending racing. The exercise test was performed on an inclined (3.5 degrees) high speed treadmill and consisted of four sequentially increasing speeds, each of 2 min duration, aiming at a final HR at or exceeding 200 bpm. HR was monitored continuously and recorded in parallel with blood sampling during the last 15 s of each speed. Blood volume determination was done with the Evans blue dye dilution technique immediately after the exercise test to ensure complete emptying of the splenic red cell reservoir. Both age and sex influenced significantly on all parameters. These were also all strongly dependent on the total red cell volume. Consequently, it was concluded that markers for work tolerance based on heart rate and blood lactate responses to submaximal treadmill exercise reliably reflect circulatory and muscle metabolic capacities. Further, individual normal values are predictable from the red cell volume alone with variation coefficients between 5 and 9.1%, or, in combination with LA200, between 4.4 and 62%. Disregarding the regression with CV, predictability of normal values is improved by considering age and sex variations.

Androgen receptors and skeletal muscle composition in trotters treated with nandrolone laureate.

To study the effects of nandrolone laureate (19-nortestosterone) on muscle hypertrophy and concentration of androgen receptors (AR), biopsy specimens were taken from the middle gluteal muscle of 6 Finnhorse trotters (geldings and mares) undergoing training before, immediately after, and 13 weeks after a 14-week treatment with nandrolone. Another 6 similarly trained horses served as controls. An additional 10 mares and 10 geldings were used to study annual variation in muscle concentration of AR. AR was immunohistochemically localized in the nuclei. AR concentration remained constant during the first 14 weeks of the study, but increased significantly during the 13-week follow-up period in both groups. This finding can be explained by the annual variation in AR. In the anabolic steroid (AS)-treated horses, but not in the controls (C), the cross-sectional area of the type I fibres increased significantly during the treatment period, and the percentage of type IIA fibres correlated positively with AR concentration at the end of nandrolone treatment. In the AS group, the concentration of DNA decreased during the 13-week follow-up period, and the percentage of H-chains in the isoenzymes of LDH increased. Protein concentration increased in both groups during the follow-up period. Glycogen content and the activity of citrate synthase in muscle during the study remained unchanged. It can thus be concluded that AS produce differing effects on type I and type II fibres, and the AR concentration in equine muscle may contribute to the change observed in the middle gluteal muscle.

Rectal biopsy diagnosis in horses with clinical signs of intestinal disorders: a retrospective study of 116 cases.

The histology from rectal biopsy specimens taken 1980-1990 on 131 occasions from 116 horses, age 1-18 years, with clinical signs of intestinal disease was evaluated and classified retrospectively. In 40 horses, autopsy results were studied for comparison. Biopsy specimens (21 horses) and post mortem rectal tissue (9 horses) from 30 healthy horses, age 4-22 years, were used as controls. In 105 clinical cases, a biopsy was performed on only one occasion, while repeat biopsy was performed in 11 cases. Specimens showed pathological changes in 60 horses. The findings were classified into acute, chronic or chronic active simple proctitis, granulomatous enteritis, eosinophilic granulomatosis/gastroenteritis, eosinophilic proctitis, erosive/ulcerative proctitis, pseudomembranous proctitis, proctitis with vasculitis and malignant lymphoma. Mild scattered neutrophil infiltration in the lamina propria was found in controls, but neutrophils in crypt or surface epithelia were abnormal findings. Depletion or hyperplasia of goblet cells sometimes accompanied inflammation. Simple proctitis occurred in association with malignant lymphoma and various inflammatory disorders of the gastrointestinal tract apparent at autopsy. Eosinophilic granulomatosis/gastroenteritis and granulomatous enteritis were diagnosed from biopsy specimens in 6 of 12 and 4 of 9 cases, respectively, of these diseases confirmed at autopsy. Reduction of acid mucins in goblet cells was a prominent feature of eosinophilic granulomatosis. Rectal biopsy was found to be a useful adjunct for evaluation of intestinal disease in the horse.

Total blood volume in the normally performing Standardbred trotter: age and sex variations.

The purposes of this study were to elucidate the influences of age and sex on the mass specific blood volume parameters: total blood volume (TBV/BW, ml/kg), plasma volume (PV/ BW, ml/kg), total red cell volume (CV/BW, ml/kg) and maximal packed cell volume (PCV, l/l, i.e. after total mobilisation of the splenic red cell reservoir) and to establish reference values for these in normally performing Standardbred trotting race horses. In total 205 horses were studied. They were all, according to their owners and/or trainers, performing satisfactorily in racing or training for shortly impending racing. Blood volume determination was done with the Evans blue dye dilution technique after exercise induced emptying of the spleen. Both age and sex were found to influence variation of these parameters significantly, with the possible exception of PV/BW, whereas the primary variation appeared to be in CV/BW. It was concluded that taking age and sex dependent variations into consideration will render prediction of normal values for the blood volume parameters in the athletic Standardbred trotter more reliable and the detection of abnormal deviations more precise if five age and sex groups are used for comparisons.

Skeletal muscle characteristics in red blood cell normovolaemic and hypervolaemic standardbred racehorses.

Muscle biopsy specimens from the middle gluteal muscle were studied in 16 red blood cell hypervolaemic (Group HV) and 19 normovolaemic (Group NV) Standardbred racehorses. All horses were stallions, 4-8 years old and having similar mean racing performance values, as described by an individual selection index value. All horses raced regularly but those in Group HV did not perform as expected and were therefore referred to the clinics for exercise tolerance testing. Muscle biopsy specimens were analysed for fibre type distribution (Type I, IIA and IIB), fibre area and relative fibre area. In addition, oxidative capacity of the fibres was evaluated by staining for nicotinamide adenine dinucleotide (NADH) tetrazolium reductase, and the activities of citrate synthase, 3-OH-acyl CoA dehydrogenase and lactate dehydrogenase were analysed in whole-muscle samples. With the exception of a higher percentage of Type IIB fibres in Group HV having a high oxidative capacity as evaluated by the NADH stain, no significant difference were found in fibre composition, fibre area or enzyme activity between the Groups HV and NV.

Metabolic response to standardised exercise test in standardbred trotters with red cell hypervolaemia.

Plasma concentrations of lactate, amino acids, ammonia and products of purine catabolism were studied before, during and after a standardised incremental exercise test in 29 Standardbred trotters admitted to the clinic for exercise tolerance testing. According to their red cell volume the horses were divided into red cell normovolaemic and red cell hypervolaemic (polycythaemic) groups. The exercise-response curve for taurine differed significantly in the two groups, whereas all the other amino acids behaved similarly. The [branched-chain amino acid]/[alanine] ratio, a proposed indicator for the use of amino acids in gluconeogenesis, was at rest significantly higher in the polycythaemic horses. Post-exercise concentrations of ammonia and allantoin, both end products of ATP breakdown, were lower in the polycythaemic horses. No differences were observed in the VLA4 and V200 markers for lactate and heart rate responses to incremental exercise, the oxidative capacity of the gluteus medius muscle, the enzyme activities or the post-exercise concentration of lactate, uric acid and hypoxanthine. It is concluded that horses with red cell hypervolaemia behave in a submaximal standardised exercise test on a treadmill in the same way as do red cell normovolaemic horses. The results suggest that the rate of amino acid utilisation in gluconeogenesis and the ability of amino acids to produce energy aerobically may be elevated in polycythaemic horses.

Skeletal muscle characteristics in young trained and untrained standardbred trotters.

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

Pulmonary gas exchange correlated to clinical signs and lung pathology in horses with chronic bronchiolitis.

Eight horses (mean weight 438 kg) with chronic obstructive pulmonary disease (COPD) were studied for clinical signs, ventilation/perfusion relationships (VA/Q) and lung morphology. Four horses were killed and necropsied after the study. In horses with COPD, minute ventilation was almost twice as high as normal, whereas PaO2 was significantly decreased. Cardiac output was normal, but pulmonary artery pressure and pulmonary vascular resistance were significantly increased. The VA/Q distribution was abnormal with an increased scatter of VA/Q ratios. However, shunt (VA/Q = 0) was increased in one horse only. Ventilation of dead space and high VA/Q regions (VA/Q greater than 10) were increased markedly and comprised 74 per cent of minute ventilation. On lung biopsy, all horses showed chronic bronchiolitis with epithelial hyperplasia and metaplasia. Diffuse acinar hyperinflation also was evident at necropsy. There was a significant inverse correlation between the respiratory rate and the fractional ventilation of normal VA/Q regions. Also, there was a significant agreement between the extent of bronchiolar epithelial hyperplasia in necropsy specimens of lungs and the degree of ventilation of high VA/Q regions and dead space. The findings suggest that hyperinflation of the lung due to obstructed airways may be the common denominator of increased ventilation of high VA/Q regions and dead space ventilation and of elevated pulmonary artery pressure in horses with COPD from chronic bronchiolitis.

Effects of a draft-loaded interval-training program on skeletal muscle in the horse.

Five Standardbred trotters were trained on a treadmill 3 times/wk for 12 wk by intervals of draft-loaded exercise. The draft load was 34 kp and the velocity approximately 7 m/s. Muscle biopsies were taken from the gluteus medius and longissimus muscles before training and after 2, 4, 8, and 12 wk of training and from the brachiocephalicus muscle before and after training. Both the percentage and the area of type IIa fibers increased and the percentage of type IIb fibers decreased in the gluteus medius muscle during the first 2 wk of training, and then no further significant difference was noted. The percentage of type I fibers increased in the brachiocephalicus muscle, and the area of type IIb fibers increased in the longissimus muscle. The citrate synthase activity increased in the gluteus muscle only, and the increase was seen during the first 2 wk. No significant differences were seen in 3-hydroxy-acyl-CoA dehydrogenase and lactate dehydrogenase activities in the muscles during the entire training period. Less glycogen was utilized in the gluteus muscle and less blood lactate accumulated when the horses performed an unloaded submaximal exercise test after compared with before training. It can be concluded that rapid changes are induced in the gluteus medius muscle when horses are trained pulling a light-draft resistance at a submaximal trotting speed.

Blood chemistry and skeletal muscle metabolic responses during and after different speeds and durations of trotting.

Eight standardbred horses trotted on a treadmill for 55 mins at a sub-maximal speed of 5m/sec and subsequently performed an exercise test consisting of 2 min intervals at increasing speed. Heart (HR) and respiratory (Rf) rates and venous blood samples were obtained before, during and for 5 mins after exercise. Gluteus medius muscle biopsies and rectal temperatures were taken before and after exercise. The mean HR was 132/min and the mean Rf was 156/min during the 5m/sec trotting. With 5m/sec exercise, plasma free fatty acids (FFA), glucose, creatinine and cortisol concentrations increased markedly. Blood lactate increased slightly and plasma potassium increased initially and then decreased with a lengthened duration of trotting. Within 5 mins post exercise plasma FFA, glucose and cortisol concentrations continued to rise, whereas creatinine and lactate levels declined slightly and potassium concentrations declined rapidly to below resting values. The mean intramuscular (im) glycogen utilisation was 86 mmol/kg, no significant changes occurred in creatine phosphate (CP), adenosine triphosphate (ATP) and glucose-6-phosphate (G-6-P) concentrations and muscle lactate decreased significantly. During the second exercise test mean HR was 215/min and Rf 126/min at top speed. No significant change was seen in plasma glucose whereas cortisol levels rose to a lesser extent, and creatinine lactate, ammonia and potassium concentrations to a greater extent, compared to 5 m/sec trotting. Post exercise, these parameters continued to increase except for creatinine which declined slightly and potassium which decreased rapidly. The mean im glycogen utilisation was 144 mmol/kg, ATP concentrations were unaltered, CP declined, lactate and G-6-P increased during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulatory and muscle metabolic responses to draught work compared to increasing trotting velocities.

Circulatory and muscle metabolic responses were studied in 10 horses which all performed incremental draught work at a low trotting speed on a treadmill (D-test) and also exercise with gradually increasing velocities (S-test). Exercise was continued until the horses could no longer maintain the weights above the floor or maintain speed trotting without changing gait to a gallop. Muscle biopsies were taken from the gluteus and the semitendinosus muscles before, and immediately after, exercise. The heart rate (HR) increased linearly with both increasing draught resistance and velocity and reached mean values of 212 and 203 beats/min, respectively. Blood lactate levels increased exponentially to mean values of 12.9 and 7.9 mmol/litre in the two tests. Both HR and blood lactate levels were significantly higher at the cessation of work in the D-test compared to the S-test. The relationship between HR and blood lactate response in the S-test was similar to that in the D-test. The red cell volume was determined after a standardised exercise tolerance test and was significantly correlated both to the weightloading and to the velocity, producing a HR of 200 beats/min. The changes seen in muscle glycogen and glucose-6-phosphate were similar in the two tests, whereas significantly higher lactate levels and lower creatine phosphate and adenosine triphosphate levels were seen in the D-test compared to the S-test. It was concluded that high oxidative capacity is of importance both for fast trotting and for draught work.(ABSTRACT TRUNCATED AT 250 WORDS)