bluuebunny/crossref_metadata_2025 huggingface dataset:
An MRI study of the effect of treadmill training on bone morphology of the central and third tarsal bones of young Thoroughbred horses
Authors: WHITTON R. C. , MURRAY RACHEL. C. , BUCKLEY C. , GOODSHIP A. E. , LEKEUX P.
Published: June 2010

Training results in marked modelling of the subchondral bone of the carpus, but the effect of training on the subchondral bone of the distal tarsal joints is unknown. The aim of this study was to determine whether training influenced modelling of the third and central tarsal bones in Thoroughbred horses. Twelve untrained Thoroughbred horses were divided into 2 groups.Group 1underwent a 19 week progressive training regimen on a high speed treadmill.Group 2were walked for 40 min daily. Images of left tarsi were obtained by magnetic resonance imaging (MRI) with a 0.5 Tesla superconducting magnet using a spin echo sequence. Sagittal and oblique sagittal slices were made perpendicular to the articular surfaces of the intertarsal joints and were analysed using image analysis software to measure the proportion of dense subchondral bone in the dorsal facet of each bone. Mean ± s.d. percentage area of dense subchondral bone in the dorsal facet of the central tarsal bone inGroup 1was 47 ± 8 medially, 46 ± 4 sagitally and 50 ± 11 dorsolateral, whereas inGroup 2it was 39 ± 16 medially, 43 ± 8 sagitally and 53 ± 7 dorsolateral. For the third tarsal bone mean ± s.d. percentage area of dense subchondral bone inGroup 1was 32 ± 10 medially, 39 ± 11 sagitally and 44 ± 8 dorsolateral, whereas inGroup 2it was 28 ± 8 medially, 37 ± 6 sagitally and 41 ± 9 dorsolaterally. There was no significant difference in percentage area of dense subchondral bone between the trained and untrained horses. An effect of treadmill training of Thoroughbred horses on modelling of the central and third tarsal bones could not be demonstrated.
Radiographic measures of bone shape in young Thoroughbreds during training for racing
Authors: DAVIES HELEN M. S. , GALE SUSAN M. , BAKER I. D. C.
Published: June 2010

The aim of this study was to determine if changes in the shape of the third metacarpal bone (MC3) during the first preparation for racing in young Thoroughbred racehorses could be measured radiographically. Lateral radiographs of each MC3 were taken when the horses commenced training, every 2 weeks for 10 weeks, and again at 6 months after the start of training. The width of the dorsal cortex (DC), palmar cortex (PC), and medulla (M) were measured at a position 2.5 cm distal to the nutrient foramen before the subject of each radiograph was identified. The following ratios were calculated: z=DC/M; RI = [(DC+PC)/M]x[DC/PC]. The results showed that the shape of the MC3 changed during training for racing and that these changes may be measured on standard lateral radiographs. The dorsal cortex became proportionately thicker than the rest of the bone dimensions in the dorsopalmar plane. The proportionate increases in dorsal cortex dimensions were greater in horses that were recorded as shin sore during racing than in horses that were racing with no recorded shin soreness.
Nerve block and intra‐articular anaesthesia of the forelimb In the sound horse
Authors: DREVEMO S. , JOHNSTON C. , ROEPSTORFF L. , GUSTåS PIA
Published: June 2010

Nerve blocks and intra‐articular anaesthesia are used extensively as routine methods in lameness evaluation. The method is based on the assumption that the technique itself does not change the movement pattern. The aim of this study was to carry out a quantitative kinematic study to confirm or reject the hypothesis that high palmar digital nerve block (HPDN) and intra‐articular fetlock joint anaesthesia (IAF) influence significantly the movement pattern of the horse.

Seven Standardbred horses trotting at 4.5 m/s were recorded at 240 Hz on a treadmill before and after anaesthesia by use of a ProReflex video system. Time variables, segment and joint angles were calculated. The high palmar digital nerve block (HPDN) resulted in a longer stance time and caused a greater fetlock joint angle range and greater maximal pastern joint angle. No systematic differences in time and angle variables were observed after intra‐articular fetlock joint anaesthesia (IAF). In conclusion, HPDN but not IAF affects locomotor pattern in sound horses. Distal limb proprioception is important in normal movement, while fetlock intra‐articular proprioception is apparently not. Interpretation of the effect of HPDN in lame individuals should incorporate more variables than maximal overextension of the fetlock joint.
The effect of training on the calcified zone of equine middle carpal articular cartilage
Authors: MURRAY RACHEL C. , WHITTON R. C. , VEDI S. , GOODSHIP A. E. , LEKEUX P.
Published: June 2010

Carpal osteochondral injury is frequently observed in strenuously trained horses. It is clear that the integrity of articular cartilage and subchondral bone are intimately related, although there is controversy about which component is the most important. Calcified cartilage provides the mechanical link between soft hyaline cartilage and stiff subchondral bone so it is essential to understand the tissue's response to exercise. Middle carpal calcified and uncalcified (hyaline) cartilage thickness was investigated in horses undergoing high‐ and low‐intensity exercise. Twelve untrained horses (18–21 months) were paired, and randomly assigned to an exercise group.Group 1underwent 19 weeks progressive high‐intensity training on a high‐speed treadmill.Group 2underwent walking exercise only. Osteochondral specimens were obtained from 8 test sites per carpus immediately after euthanasia. Histomorphometric measurements of total cartilage, hyaline layer, and calcified zone thickness were obtained from decalcified and undecalcified samples. Mean ± s.d. (μm) calcified cartilage thickness for dorsal cartilage fromGroup 1was 271 ± 73 and fromGroup 2was 163 ± 49; for palmar cartilage fromGroup 1was 195 ± 42 andGroup 2was 150 ± 52.Group 1horses had significantly thicker total cartilage (P<.0001) and calcified zone (P<.0001) thanGroup 2, but there was no difference in hyaline layer. Within each group all dorsal sites had thicker calcified cartilage (P<.003) than palmar sites, but no difference in hyaline or total cartilage. These findings indicate that high‐intensity exercise leads to greater calcified zone depth without alteration in hyaline cartilage thickness, and that this response is maximal at sites that withstand high, intermittent loads. Increasing calcified cartilage thickness with exercise may maintain the articular surface stiffness gradient in the face of alterations in hyaline cartilage and/or subchondral bone stiffness.
Muscle adenine nucleotide degradation during submaximal treadmill exercise to fatigue
Authors: ESSÉN‐GUSTAVSSON BIRGITTA , GOTTLIEB‐VEDI MARIANNE , LINDHOLM A.
Published: June 2010

The aim was to investigate metabolic response in muscle during submaximal treadmill exercise to fatigue, with a special emphasis on adenine nucleotide degradation products such as inosine monophosphate (IMP) in muscle and hypoxanthine, xanthine and uric acid in plasma. Five Standardbred trotters performed treadmill exercise on 2 occasions, once at 7 m/s and once at 10 m/s. Venous blood samples were taken at rest, during exercise and at the end of exercise. Muscle biopsies were taken before and after exercise and muscle temperature was measured before and after exercise. Running time differed among horses and was 48–58 min at 7 m/s and 10–15.5 min at 10 m/s. Both lactate and uric acid concentrations in plasma showed a gradual increase during exercise at both 7 and 10 m/s. At the end of exercise, values for uric acid were higher and values for lactate lower at 7 m/s compared with at 10 m/s. No marked changes were seen in plasma concentrations of hypoxanthine or xanthine with exercise.

Muscle glycogen decreased after exercise at both 7 and 10 m/s with a marked depletion seen in some fibres. Muscle lactate concentrations increased after exercise at both 7 m/s and at 10 m/s. No significant changes were seen in adenosine triphosphate (ATP), ADP and AMP concentrations, whereas IMP concentrations increased after exercise at both 7 m/s and at 10 m/s. The results of this study indicate that AMP deamination occurs with submaximal exercise and that development of fatigue may be related to adenine nucleotide degradation in muscle.
Skeletal muscle Na+‐K+‐ATPase and K+homeostasis during exercise: effects of short‐term training
Authors: McCUTCHEON L. JILL , GEOR R. J. , SHEN HUA
Published: June 2010

The objective of this study was to determine the effects of 10 consecutive days of moderate intensity training on 1) the concentration of middle gluteal muscle Na+‐K+‐ATPase as determined by vanadate‐facilitated [3H]ouabain binding; and 2) plasma potassium regulation before, during and after exercise at 100% of the pre‐training maximum rate of oxygen consumption (V̇o2max). Six mature, unfit Thoroughbred horses completed both incremental (for determination of V̇o2max) and high‐intensity exercise protocols before (HI1) and after (HI2) training. Three additional horses undertook no training or exercise tests and served as controls for determination of middle gluteal muscle Na+‐K+‐ATPase concentration. Training consisted of 10 consecutive days of running at 55% V̇o2maxfor 60 min per day (13–14 km/day). For each high intensity exercise protocol, horses completed a 10 min warm‐up at 50% V̇o2max, followed by exercise at 100% of pre‐training V̇o2max(6° incline, mean speed 9.8 m/s) until fatigue. Training resulted in a 13.8% increase in resting plasma volume (pre: 20.9 ± 0.8 1; post: 23.8 ± 0.9 1; P = 0.03), and an 8.9% increase in V̇o2max(pre: 142 ± 4 ml/kg/min; post: 155 ± 4 ml/kg/min; P=0.004) during HI. Peak values for plasma potassium concentration and content during exercise decreased by 13% (P=0.02) and 7% (P = 0.0002), respectively, after training whereas training had no effect on increases in packed cell volume, plasma total solids, and erythrocyte K+concentration and content during exercise. Following training, there was also a significant (23%) increase in Na+‐K+‐ATPase concentration in biopsies of middle gluteal muscle, as measured by vanadate‐facilitated [3H]ouabain binding. We conclude that 10 days of moderate intensity exercise results in increases in skeletal muscle Na+‐K+‐ATPase and attenuation in the elevation in plasma K+during high intensity exercise at the same absolute workload. The increase in middle gluteal muscle Na+‐K+‐ATPase concentration is consistent with decreases in K+efflux from working muscle during exercise.
Skeletal myosin heavy chain composition and carriage training
Authors: RIVERO J. L. L. , SERRANO A. L.
Published: June 2010

Three different myosin heavy chain (MHC) isoforms have been identified in the equine gluteus medius muscle: the slow or MHC‐I and the 2 fast MHC‐IIA and MHC‐IIX isoforms. They are distributed in 3 fibre types containing a single MHC (I, IIA, IIX) and 2 hybrid types co‐expressing 2 isoforms (I+IIA, IIA+IIX). The aim of this study was to determine if heavy carriage training alters skeletal MHC composition in horses. Fourteen Andalusian mares age 42–46 months were used. Seven horses were used as controls to estimate the effects of growth on muscle. The remaining 7 horses underwent a training programme based on carriage exercise for 8 months. The intensity of exercise was individually adjusted to each horse according to a standardised exercise test. Gluteus medius muscle biopsies were analysed biochemically for MHC composition by electrophoresis, immunohistochemically for fibre types with specific anti‐MHC monoclonal antibodies, and histochemically for fibre type areas, fibre oxidative capacity and capillaries. After training, MHC‐IIIX decreased and MHC‐I increased. The percentages of type IIX and IIAX (i.e. fibres co‐expressing MHCs IIA and IIX) fibres decreased, whereas the percentage of type I fibres increased. Neither MHC‐IIA composition nor type IIA fibre percentage changed with training. The training had no significant effect on fibre areas and capillaries, but the percentage of fibres with high oxidative capacity increased. The control group showed no changes in muscle variables after the 8 month training period. These results suggest that carriage training alters MHC composition in equine skeletal muscle, reflecting a conversion of MHC isoforms in the order IIX→ IIA→ I and suggesting a reduction in the velocity of shortening of the muscle, but an increase in fatigue resistance.
Blood glucose clearance after feeding and exercise in polysaccharide storage myopathy
Authors: DE LA CORTE F. D. , VALBERG STEPHANIE J. , MICKELSON J. R. , HOWER‐MORITZ MELISSA
Published: June 2010

Polysaccharide storage myopathy (PSSM) in Quarter Horses (QH) and QH crosses is a glycogen storage disorder in which blood glucose clearance and insulin sensitivity, following an i.v. or oral glucose challenge, are enhanced. Exercise is known also to enhance glucose uptake into skeletal muscle in many animal species. Therefore, the purpose of this study was to compare the effect of exercise on glucose clearance in PSSM and control horses when an oral carbohydrate meal (8 Mcal sweet feed) was fed following either 12 h fasting alone (NEX protocol) or following fasting and a standard exercise protocol (EX protocol). In the NEX protocol, horses fasted 12 h and then were fed 8 megacalories (Meal) of sweet feed (2.3 kg). In the EX protocol, horses were fed sweet feed 2 h after an exercise test (SET). Blood glucose was analysed for >480 min after feeding. Muscle biopsies were taken before and after the EX protocol. With the NEX protocol, the mean of all blood glucose and insulin concentrations were significantly lower in fed‐PSSM horses than controls (P<.013). The EX protocol in control horses caused a less pronounced percentage change in glucose concentration from baseline following feeding compared to the NEX protocol (mean peak EX 26.5% vs. NEX 70.2%, respectively) (P<.0003). In PSSM horses, the EX protocol also resulted in a lower percent change in glucose concentration following feeding compared to the NEX protocol (44.7 vs. 67.5%, respectively) (P=0.021). The magnitude of the difference in percentage change of blood glucose concentration with the EX protocol was less in PSSM than that seen for controls (mean peak PSSM‐EX 44.7% vs. 26.5% for controls, respectively) (P<.006). No significant differences in the insulin:glucose ratios were found for control horses between NEX and EX. In PSSM horses, the insulin:glucose ratio was significantly increased in the EX vs. NEX. In conclusion, exercise in normal horses results in enhanced glucose clearance following feeding without altering insulin:glucose ratios. At rest, PSSM horses have lower insulin:glucose ratios after feeding than normal horses, however, exercise in PSSM horses significantly increases insulin:glucose ratios. This may explain the beneficial effect of daily exercise for preventing rhabdomyolysis in horses with PSSM.
Effects of conditioning horses with lactate‐guided exercise on muscle glycogen content
Authors: GANSEN SILKE , LINDNER A. , MARX S. , MOSEN H. , SALLMANN H.‐P.
Published: June 2010

The effects of 3 different conditioning programmes on muscle glycogen concentration in horses were examined. Speed of exercise was selected according to the blood lactate values for each horse derived from a standardised exercise test before beginning a conditioning programme. Six 2‐year‐old Haflinger stallions were assigned randomly to one of 3 conditioning programmes according to a 6 × 3 latin square design: 45 min at their individualv1.5orv2.5and 25 min atv4. Each conditioning programme lasted 6 weeks (21 exercise sessions), followed by 5 weeks without conditioning (resting period). All exercise was carried out on a treadmill inclined at 17%. Muscle biopsies were taken 5 times from thegluteus mediusmuscle at 2 cm and 6 cm depth: before the start and in the middle of the conditioning period, then at Days 2, 9 and 35 after the last exercise session. It was found that glycogen concentration was not affected by conditioning until 9 days after finishing conditioning atv1.5andv2.5for 45 min (P<.05). By this time glycogen concentration in the muscle samples taken at 6 cm depth increased by 47 and 48%, respectively, and remained elevated until the end of the resting period.

It was concluded that conditioning at lower intensity and for longer duration seemed to increase glycogen stores in the muscle while faster intensity but shorter duration exercise did not. To increase the likelihood of measuring effects of conditioning programmes on muscle variables, sampling should be done at different depths of a muscle and at several days after finishing a conditioning programme.
Contributions of equine exercise physiology research to the success of the 1996 Equestrian Olympic Games: a review
Authors: JEFFCOTT L. B. , KOHN C. W.
Published: June 2010

Following public concern about the weather conditions for the 1996 Olympic Games in Atlanta an international research programme was initiated. The primary objective of this effort was to identify strategies for ensuring welfare of horses competing in the heat. Field observations of horses during the endurance test of 3‐day events in Europe, Canada, and the USA characterised the work effort of this form of competition; laboratory treadmill studies assessed limitations to performance of heat and humidity, explored the relationships of thermoregulatory demands to the phases of the competition and documented fluid and electrolyte losses. Estimates of energy expenditure and heat production during the endurance test were made. Strategies for facilitating heat dissipation were also studied in depth. Assessment of the effect of environmental conditions was based upon intensive climate monitoring using a modification of the Wet Bulb Globe Temperature index. Studies of heat acclimation provided a basis for recommendation of acclimatisation times for horses before the Games. The results of all these studies guided the management of equine athletes at the 1996 Olympic Games and significantly advanced knowledge of thermoregulation in competitive horses.
Thermoregulatory strategies during short‐term exercise at different intensities
Authors: SCOTT CAROLINE M. , MARLIN D. J. , SCHROTER R. C.
Published: June 2010

Previously we have observed a decline in sweating rate (SR) during high intensity exercise in an incremental test protocol. In man, the sweating sensitivity (SR/°C) has been shown to vary with exercise intensity. The aim of the present study was to determine if thermoregulatory responses in the horse, a prolific sweater with a high rate of metabolic heat production, were modified by exercise intensity. The effect of 3 separate exercise intensities (50 (S), 70 (M) and 90% (F) V̇o2Peakon neck (SRN) and gluteal sweating rate (SRG), pulmonary artery (TPA), rectal (TREC) and skin temperatures on the neck (TSK‐N) and gluteal region (TSK‐G) were investigated. Horses were exercised for ˜2 min at each exercise intensity in a randomised order. The rate of increase in TPAincreased with exercise intensity (P<.05) (0.27 ± 0.05, 0.43 ± 0.04 and 0.77 ± 0.05°C/min during S, M and F, respectively. The TPAand TSKtemperatures at the onset of sweating were not different between exercise intensities (P>0.05). Despite the increased rate of heat production with increasing exercise intensity, sweating sensitivity decreased on both the neck [(P<.05) (18.2 ± 3.4 (S), 12.0 ± 3.5 (M) and 2.9 ± 0.7 (g/m2/min)/°C (F)] and gluteal region [(P<.05) (8.9 ± 2.0 (S), 5.1 ± 1.7 (M) and 0.8 ± 0.3 (g/m2/min)/°C (F)]. During exercise at 90% V̇o2peaksweating sensitivity and the rate of increase in skin temperature were markedly reduced compared to at 70% V̇o2peak. The present investigation demonstrates that the drive to thermoregulate is overridden during short‐term, high‐intensity exercise, resulting in greater heat storage (TPA) as a result of a lower SR sensitivity.
Effects of frusemide on electrolyte and acid‐base balance during exercise
Authors: CARLSON G. P. , JONES J. H.
Published: June 2010

This study was undertaken to evaluate the effects of frusemide on the concentration of plasma electrolytes and the relationship between changes in electrolyte concentration and the simultaneous changes in acid‐base balance in arterial and venous blood during intense exercise. Five exercise‐conditioned Thoroughbred horses were exercised on a highspeed treadmill at a slope of 10% at speeds known to exceed V̇o2max. Horses participated in 3 randomised exercise trials in which they received either placebo (control), low‐dose frusemide (0.5 mg/kg bwt), or high‐dose frusemide (1.0 mg/kg) 4 h prior to exercise. Arterial and mixed venous blood samples were drawn before, during and after intense exercise. Packed cell volume (PCV), plasma protein, plasma electrolyte, plasma lactate concentrations and acid‐base balance were determined. Frusemide at both dosages induced a significant metabolic alkalosis associated with a decrease in plasma [chloride] in both arterial and mixed venous blood. There was a highly significant correlation between the strong ion difference (SID) and [bicarbonate] in all blood samples. The effects of frusemide on electrolyte concentration and acid‐base balance were largely due to changes in SID.
Environmental stress and 3‐day eventing: effects of altitude
Authors: FOREMAN J. H. , WALDSMITH J. K. , LALUM R. B.
Published: June 2010

Three‐day event horses are subject to various external environmental stresses including changes in ambient temperature, humidity, altitude, and test severity. Considerable research on the adverse effects of increased heat and humidity preceded the 1996 Olympic Summer Games in Atlanta, Georgia USA, but no research has been done previously on the effects of altitude on 3‐day eventing. Physical and venous blood gas data were collected on horses (n = 24) competing in the High Prairie Preliminary (CCN*) and Intermediate (CCN**) 3‐day events and Preliminary Horse Trials in Parker, Colorado (1900 m above sea level). Despite the increased altitude, only post exercise rectal temperature and pH were higher (P<.05) whereas heart rate (HR), [K+], and ionised calcium (iCa++) were lower (P<.05) in 3‐day event horses compared to horse trial horses. All other variables (respiratory rate [RR], PCV, [Hb], Pco2, [tco2], [HCO3‐], BE, and [Na+]) were not different between groups (P>0.05). When these preliminary horse trial horses in Colorado were compared to those previously studied at preliminary horse trials at sea level in Arizona, post exercise HR and RR were higher (P<.05) and pH, Pco2, [tco2], [HCO3‐], BE and [iCa++] were lower (P<.05) at altitude. These data show that increased altitude (1900 m above sea level) was more stressful for 3‐day event horses, but did not result in the severe physiological changes and inability to complete prescribed exercise tests seen in previous studies with increased heat and humidity. It is clear from these and previous data that increased heat and humidity are the more important environmental stressors in 3‐day eventing.
Sweat production and localisation of carbonic anhydrase in the equine sweat gland during exercise at two ambient temperatures
Authors: DAHLBORN KRISTINA , JANSSON ANNA , NYMAN SARA , MORGAN KARIN , HOLM LENA , RIDDERSTRåLE YVONNE
Published: June 2010

The aim of this investigation was to study sweat production during exercise at 2 ambient temperatures (20°C and 35°C) and the concurrent localisation of carbonic anhydrase (CA) in the sweat gland. Horses develop alkalosis during prolonged exercise and the sweat contains HCO3‐. Carbonic anhydrase is therefore of interest since it catalyses the reaction CO2+ H2O ↔ HCO3‐ + H+. Four standardbred trotters performed an exercise test. Skin biopsies were taken from the neck, and sweat rate, blood and skin temperatures were measured. There was a close relationship between sweat rate, temperatures and work intensity at 20°C. Temperatures and sweat rate were higher at 35°C and did not fall when the work intensity dropped. A significant decrease in the sweat gland cell area was found after exercise at 35°C with an accompanying decrease of vesicles. Strong CA activity was present at the luminal cell membrane and weaker basolaterally. The staining intensity increased after exercise. We suggest that CA might be of importance for counteracting the alkalosis developed after exercise by delivering HCO3‐ for generation of the alkaline pH in sweat.
Effects of potassium intake on potassium, sodium and fluid balance in exercising horses
Authors: JANSSON ANNA , LINDHOLM A. , LINDBERG J. E. , DAHLBORN KRISTINA
Published: June 2010

The aim of this study was to investigate the adaptation to an increased potassium (K+) intake in horses and to study whether the regulation of the post exercise K+, sodium (Na+) and fluid balances were altered by an increased K+ intake. Four Standardbred horses were fed 2 levels (4.1 and 5.4 mmol/kg bwt/day) of K+ for 17 days in a crossover design. The effects on K+, Na+ and fluid balance were studied both at rest and in response to 29 km exercise. K+, Na+ and fluid intakes and outputs were balanced within 24 h after a new diet had been introduced. Adaptation consisted primarily of an increased urinary K+ excretion, later followed by an increase in faecal excretion. The increased urinary K+ excretion was associated with an increased mass of urine (1.2–1.4 kg/day) compensated for by an increased water intake. The sweat Na+ concentration was increased on the highest K+ intake (from 123 ± 5 mmol/l to 138 ± 3 mmol/l) and the urinary Na+ excretion was lower post exercise on this diet. There were no differences in the magnitude of post exercise hypokalaemia between the diets, and plasma K+ concentration was still reduced 24 h post exercise even when the horses were fed the higher K+ diet. Adaptation to an increased K+ intake was rapid in these horses and consisted mainly of an increased urinary excretion. The response to exercise was unaltered by the increased K+ intake, except for an increased Na+ concentration in sweat.
Electrolyte and glycerol supplementation improve water intake by horses performing a simulated 60 km endurance ride
Authors: DüSTERDIECK KATJA F. , II H. C. SCHOTT , EBERHART SUSAN W. , WOODY KRISTINA A. , COENEN M.
Published: June 2010

To replace electrolytes lost in sweat during endurance competitions, riders frequently supplement horses with hypertonic oral electrolyte pastes. To determine whether this practice and concurrent administration of the so‐called hyperhydrating substance glycerol are of benefit, weight loss, voluntary water intake, plasma osmolality, and plasma protein and electrolyte concentrations were measured in 6 Arabian horses supplemented with a total of 2.4 ml/kg bwt of water (W); 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 ml/kg bwt of water (E); or 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 ml/kg bwt (3 g/kg bwt) of glycerol (GE) before and during a treadmill exercise test simulating a 60 km endurance ride. Weight loss was greater (P<.01) with W (3.2%) than with E and GE (1.0% and 0.9%, respectively) and was associated (r=‐0.85, P<.0001) with less (P<.01) water intake with W (12.2 l) than with E or GE (23.5 l and 25.81, respectively). Plasma osmolality increased to a greater extent (P<.01) with GE than with E and was unchanged with W. In contrast, plasma protein concentration decreased (P<.01) in the later stages of the simulated ride with E and GE, reflecting plasma volume expansion, but remained unchanged with W. Plasma Na+and Cl−concentrations increased (P<.01) with E and GE and were greater (P<.01) than values for W during the second half of the 60 km simulated ride. Despite administration are large amounts of potassium with E and GE, plasma K+concentration was decreased (P<.01) at the end of the rest breaks during the simulated ride and after 60 min of recovery with all supplements. Adverse effects of administration of hypertonic oral electrolyte pastes were not observed and decreases in plasma protein concentration within 30 min after drinking with all supplements suggested that intestinal absorption was well maintained during the simulated endurance ride. In conclusion, electrolyte supplementation in the form of hypertonic oral pastes improved water intake during endurance exercise but concurrent glycerol administration provided no additional benefits in comparison to supplementation with electrolytes alone.
Electrolyte vs. glucose‐electrolyte isotonic solutions for oral rehydration therapy in horses
Authors: MONREAL L. , GARZóN N. , ESPADA Y. , RUIZ‐GOPEGUI R. , HOMEDES J.
Published: June 2010

An isotonic electrolyte solution with a composition similar to equine sweat was compared to an isotonic glucose‐glycine‐electrolyte solution for oral rehydration therapy in exercising horses. Ten horses were dehydrated by using frusemide and allocated randomly to receive 4 different oral solutions: isotonic sweat‐like electrolyte solution, half‐strength hypotonic electrolyte solution, isotonic glucose‐glycine‐electrolyte solution, and plain water. Solutions were given by nasogastric tube using the same volume as the bodyweight lost by each horse. Blood samples were collected before and throughout 6 h of the rehydration period. Results showed that all solutions recovered pre‐frusemide values of packed cell volume (PCV) and total plasma protein (TP) in a similar fashion. No changes for Na+values were observed during the rehydration period when the isotonic sweat‐like solution was used. However, a significant hyponatraemia was induced throughout rehydration when the other 3 solutions were given, especially when hypotonic solution and water were used. Osmolality values did not change when both isotonic solutions were administered; but a significant hypotonicity was observed when hypotonic solution and water were given. When the isotonic sweat‐like solution was used, plasma Cl−, K+and creatinine values recovered to premedication values significantly faster than the other 3 solutions. In conclusion, the isotonic sweat‐like electrolyte was the best solution because it restored rapidly the fluid and plasma electrolyte imbalances. In contrast, the isotonic glucose‐glycine‐electrolyte solution impaired the plasma electrolyte imbalances.
Weak acid‐concentration Atotand dissociation constant Kaof plasma proteins in racehorses
Authors: STäMPFLI H. R. , MISIASZEK S. , LUMSDEN J. H. , CARLSON G. P. , HEIGENHAUSER G. J. F.
Published: June 2010

The plasma proteins are a significant contributor to the total weak acid concentration as a net anionic charge. Due to potential species difference, species‐specific values must be confirmed for the weak acid anionic concentrations of proteins (Atot) and the effective dissociation constant for plasma weak acids (Ka). We studied the net anion load Atotof equine plasma protein in 10 clinically healthy mature Standardbred horses. A multi‐step titration procedure, using a tonometer covering a titration range of PCO2from 25 to 145 mmHg at 37°C, was applied on the plasma of these 10 horses. Blood gases (pH, PCO2) and electrolytes required to calculate the strong ion difference ([SID] = [(Na++K++Ca2++Mg2+)‐(Cl−+Lac+PO42‐)]) were simultaneously measured over a physiological pH range from 6.90–7.55. A nonlinear regression iteration to determine Atotand Kawas performed using polygonal regression curve fitting applied to the electrical neutrality equation of the physico‐chemical system. The average anion‐load Atotfor plasma protein of 10 Standardbred horses was 14.89 ± 0.8 mEq/l plasma and Kawas 2.11 ± 0.50 × 10−7Eq/l (pKa= 6.67). The derived conversion factor (iterated Atotconcentration/average plasma protein concentration) for calculation of Atotin plasma is 0.21 mEq/g protein (protein‐unit: g/l). This value compares closely with the 0.24 mEq/g protein determined by titration of Van Slykeet al.(1928) and 0.22 mEq/g protein recently published by Constable (1997) for horse plasma. The Ka value compares closely with the value experimentally determined by Constable in 1997 (2.22 × 107Eq/l). Linear regression of a set of experimental data from 5 Thoroughbred horses on a treadmill exercise test, showed excellent correlation with the regression lines not different from identity for the calculated and measured variables pH, HCO3and SID. Knowledge of Atotand Kafor the horse is useful especially in exercise studies and in clinical conditions to quantify the mechanisms of the acid‐base disturbances occurring.
Effect of diet on Thoroughbred horses with recurrent exertional rhabdomyolysis performing a standardised exercise test
Authors: MacLEAY JENNIFER M. , VALBERG STEPHANIE J. , PAGAN J. D. , DE LA CORTE F. , ROBERTS JENNIFER , BILLSTROM JESSICA , McGINNITY JILL , KAESE HEATHER
Published: June 2010

Previous studies have associated recurrent exertional rhabdomyolysis (RER) with a diet high in soluble carbohydrate (CHO). The purpose of this study was to investigate the effect of 3 diets on clinical and metabolic parameters in 5 Thoroughbred horses with RER and 3 healthy Thoroughbreds performing a standardised exercise test (SET). Two diets were formulated to meet energy requirements for the amount of exercise being performed in the form of CHO or fat (21.4 Meal DE/day). The third diet was formulated to provide 135% of the DE of the other 2 diets in the form of an excessive amount of carbohydrate (28.8 Meal DE/day). Diets were fed in a crossover design for 3 week blocks and then horses performed a near maximal SET. Changes in heart rate (HR), plasma lactate, plasma glucose, total plasma solids, packed cell volume (PCV), muscle lactate and muscle glycogen concentration were measured immediately prior to, during, and 5 min after exercise. Serum creatine kinase (CK) activity was measured prior to and 4 h post SET. A 2‐way ANOVA was used to examine the effect of group and dietary treatment. When dietary treatments were compared, horses fed the high‐CHO diet had a mean pre‐SET PCV and pre‐SET HR that was higher than horses fed the fat diet (P=0.06 and P=0.07, respectively). Pre‐SET heart rates were highest in RER horses consuming the high‐CHO diet compared to RER horses consuming the low‐CHO and fat diets (P = 0.02). Horses with RER had 4 h post SET CK activity greater than 400 u/l in 7/14 (50%) measurements compared to control horses which had CK activity greater than 400 u/l in 2/7 (29%) measurements. This study did not demonstrate a significant effect of diet on rhabdomyolysis, indicated by CK activity, or on the metabolic response to exercise. However, diet may have a calming effect on Thoroughbred horses with RER as manifested by decreased pre‐exercise heart rates and decreased pre‐exercise PCV in horses fed the fat diet.
Dietary fat supplementation and equine plasma lipid metabolism
Authors: GEELEN SUZANNE N. J. , van OLDRUITENBORGH‐OOSTERBAAN MARIANNE M.SLOET , BEYNEN A. C.
Published: June 2010

Feeding of a fat‐rich diet to horses may enhance the flux of fatty acids, in the form of triacylglycerols (TAG), through the circulation into skeletal muscle. This hypothesis was tested indirectly by measuring the concentration of plasma TAG and the activity of lipoprotein lipase (LPL) in post heparin plasma. Six mature horses were fed a high‐fat or a control diet according to a crossover design with feeding periods of 6 weeks. The control diet contained 1.5% fat in the dry matter and the high‐fat diet 11.8%. The high‐fat diet was formulated by adding soybean oil to the control diet at the expense of an isoenergetic amount of corn starch plus glucose. Both diets consisted of hay and concentrate and were given on a restricted basis. Nine hours after feeding, whole plasma TAG concentration decreased significantly by 84% following fat‐supplementation, whereas the whole plasma concentrations of cholesterol and phospholipids were significantly increased by 53% and 26%, respectively. The level of HDL‐cholesterol was raised by 54%. The changes in plasma lipids were accompanied by a 79% increase in LPL activity in post heparin plasma. These results indicate that in the fasting state a high‐fat diet raises the flux of fatty acids, in the form of TAG, into skeletal muscles as illustrated by the observed decrease in plasma TAG concentrations and increase in LPL activity. It is speculated that the increased flux of fatty acids is associated with an increased oxidative capacity of skeletal muscle which might be advantageous to exercising horses.
Time of feeding and fat supplementation affect plasma concentrations of insulin and metabolites during exercise
Authors: DUREN S. E. , PAGAN J. D. , HARRIS PAT A. , CRANDELL KATHLEEN G.
Published: June 2010

Six Thoroughbreds were used to evaluate time of feeding on changes in exercise response in horses receiving either a textured feed or a fat‐supplemented textured feed. Using a crossover design, 3 horses were fed a fat‐supplemented diet while 3 horses received a control ration of textured feed. Horses performed a standardised exercise test (SET) on a high speed treadmill. The SET was performed at 3 different times: 1) following an overnight 12 h fast, 2) 3 h after feeding and 3) 8 h after feeding. The SET consisted of a 2 min walk at 1.4 m/s, 800 m trot at 4.2 m/s, 800 m gallop at 7.7 m/s, 1600 m gallop at 11 m/s, 800 m trot at 4.2 m/s and 2 min walk at 1.4 m/s. Jugular blood samples were taken before feeding, hourly until the beginning of the SET, at the end of each exercise step, 15 min post exercise and 30 min post exercise. During the SET, heart rate was measured and blood samples collected for analysis of glucose, lactate, insulin and nonesterified fatty acids (NEFA). Feeding horses 3 h prior to exercise resulted in elevated concentrations of plasma glucose and insulin (P<.01) at rest Elevated concentrations of insulin in horses fed 3 h prior to exercise decreased plasma glucose (P<.01) during exercise and appeared to have suppressed fat oxidation during exercise because horses that were either fasted or fed 8 h post prandial had a net disappearance of NEFA in the plasma during exercise. This study indicates that beginning exercise with elevated plasma insulin appeared to be of no benefit during the exercise conducted in this experiment.
Digestible energy expenditure in grazing activity of growing horses
Authors: ASAI Y. , MATSUI A. , OSAWA T. , KAWAI M. , KONDO S.
Published: June 2010

Ten Thoroughbred yearlings (5 females and 5 males) were used to examine the effect of time of grazing on pasture forage and digestible energy (DE) intake, bodyweight gain and DE expenditure in grazing activity. Five females were grazed for 17 h/day (LTG), 5 males were grazed for 7 h/day (STG) and they were fed differently. As a result, DE intake from pasture forage of LTG horses and STG horses was 27.3 and 12.7–13.9 Meal/day, respectively. The average daily gain (ADG) of LTG and STG horses was 0.37 and 0.39–0.61 kg/day, respectively. The regression lines between DE intake and ADG of both groups were parallel and the difference in DE intake between them was 10 Meal of DE. It was suggested that DE expenditure in grazing activity (entirely at night) of growing horses was 1 Mcal/h under the conditions of this study.
Effect of a post exercise fat‐supplemented diet on muscle glycogen repletion
Authors: HYYPPä S. , SAASTAMOINEN M. , PÖSÖ A. REETA
Published: June 2010

Low muscle glycogen at the beginning of exercise may adversely affect performance, increase protein degradation and contribute to the onset of fatigue. As horses are sometimes required to compete on consecutive days both in racing and endurance types of competition, optimal muscle glycogen repletion may improve performance on the day following a race day. The purpose of this experiment was to study the effects of fat supplementation on repletion of muscle glycogen. Twelve Finnhorses performed an exercise test on a treadmill, and 2 and 4 h later they received hay and concentrate(Trial A).Two weeks later these horses performed the same exercise test and were fed the same diet supplemented with either 1000 g of carbohydrate or 400 g of vegetable oil(Trial B).A third trial(Trial C)was 3 weeks later, identical to Trial B, except that the fat group had already been adapted to dietary fat for 3 weeks. Blood samples were analysed for lactate, glucose, glycerol, triglycerides, NEFA, cholesterol, β—OH‐butyrate, insulin and glucagon and muscle samples were analysed for glycogen and triglycerides. The results indicate that in horses not adapted to fat feeding, fat supplementation slows the rate of muscle glycogen repletion, and that after an adaptation period, fat supplementation does not alter the rate of muscle glycogen repletion compared to the rate with a normal diet.
The effect of dietary fibre on hydration status after dehydration with frusemide
Authors: WARREN LORI K. , LAWRENCE L. M. , BREWSTER‐BARNES TAMMY , POWELL DEBRA M.
Published: June 2010

Three diets were fed to 6 horses in a 3 × 6 Latin rectangle experiment to determine if dietary fibre could improve hydration status in response to dehydration with frusemide. Frusemide was used to simulate dehydration from exercise‐induced sweat loss. Diets contained similar dry matter (DM), energy, protein and electrolyte content, but differed in total dietary fibre (TDF) and/or soluble fibre (SDF). The 3 diets were: 1) HIGH‐HIGH (high TDF, high SDF); 2) HIGH‐LOW (high TDF, low SDF); and 3) LOW‐LOW (low TDF, low SDF). In each 10 day period, water intake and faecal moisture content were assessed on Day 7. On Day 10, feed and water were withheld and horses were dehydrated with frusemide (1 mg/kg bwt, i.m.). Plasma volume (PV), plasma total protein (TP), packed cell volume (PCV) and plasma electrolyte concentrations were determined before and after frusemide administration. Water consumption was greater (P<.05) when horses received diets high in TDF. Faecal moisture content was greatest (P<.01) when horses received the HIGH‐HIGH diet. The decline in PV and the rise in plasma TP concentration following frusemide administration were similar for all diets. When horses received the HIGH‐HIGH diet, they had a greater (P<.05) bodyweight before dehydration and lost more (P<.05) bodyweight in response to frusemide. A greater loss of bodyweight in response to frusemide without a proportional loss of PV when horses received the HIGH‐HIGH diet suggests that a diet high in SDF may provide the horse with a source of dispensable water in the hind gut during dehydration.
Repeated administration of frusemide does not offer an advantage over single dosing in attenuating exercise‐induced pulmonary hypertension in Thoroughbred horses
Authors: GOETZ T. E. , MANOHAR M. , MAGID J. H.
Published: June 2010

The objective of the present study was to ascertain whether administration of a second dose of frusemide would attenuate exercise‐induced pulmonary hypertension more than a single dose. Right atrial, right ventricular and pulmonary vascular pressures were determined in 7 healthy, sound, exercise‐trained Thoroughbred horses at rest and during exercise (14.2 m/s + a 3.5% uphill grade) performed at maximal heart rate (217 ± 3 beats/min [mean ± s.e.]). Horses were studied during the following 3 treatments in random order 7 days apart: control (no medication), frusemide single dose (250 mg i.v. 4 h pre‐exercise), and frusemide double dose (250 mg i.v., 4 h pre‐exercise + 250 mg i.v. 2 h pre‐exercise). In the control study, exercise resulted in significant (P<.05) right atrial as well as pulmonary arterial, capillary and venous hypertension. In the frusemide single dose experiments, a significant (P<.05) attenuation of the exercise‐induced rise in right atrial and pulmonary vascular pressures was observed. However, compared with frusemide single dose experiments, significant changes in the exercise‐induced right atrial and pulmonary arterial, capillary and venous hypertension were not observed in the frusemide double dose experiments. Therefore, it is concluded that administration of an additional dose of frusemide is unlikely to affect the severity of EIPH in racing Thoroughbred horses more than a single dose.
Osteoinductive response in the dorsal aspect of the carpus of young Thoroughbreds in training occurs within months
Authors: FIRTH E. C. , GOODSHIP A. E. , DELAHUNT J. , SMITH T.
Published: June 2010

Bone mineral density (BMD) was measured by dual x‐ray absorptiometry (DXA) in the carpus of 6 Thoroughbreds age 24 months that were exercised on the treadmill for 4.5 months, and of 6 matched control horses. A sagittal slab of known thickness was sawn from one or more of radius, radial carpal (Cr), third carpal (C3), and third metacarpal (Mc3) bones. After the 4.5 month treadmill exercise, there was a significantly greater volumetric BMD in the dorsal aspect of C3 (P=0.006). Treadmill‐exercised horses also had higher BMD in the dorsodistal aspect of the radius (P=0.03), the dorsal half of Mc3 (P=0.012), and the dorsal aspect of Cr (P = 0.04). In other areas of interest (AOI) studied on the palmar aspect of the bones, significant increases in exercised horses did not occur. These sizeable changes in bone mass occurred within a few months of initiation of exercise. With technical development, DXA could be appliedin vivofor investigation of changes in bone mass of horses which are growing and exercising under various regimes. The data are also relevant to the development of scientifically based training protocols.
Effect of exercise on bone density in distal regions of the equine third metacarpal bone in 2‐year‐old Thoroughbreds
Authors: RIGGS C. M. , BOYDE A.
Published: June 2010

The present study addressed the question of whether training induces changes in bone density in the younger racehorse in regions relevant to the genesis of the common sagittal condylar fracture pattern and, if so, the nature of such alteration. Third metacarpal bones (McIII) were obtained from 12 experimental Thoroughbred, unbroken fillies, age 18.1–21.0 months at entry to the study. Six(Group E)undertook 19 weeks of progressive high intensity exercise on a high‐speed treadmill at 3% incline. Six(Group C)walked 40 min each day. Clinical bone density was studied by Computed Tomography (CT) of the right Mein. 1:1 aspects of bone density were studied by digital radiography of slices and microscopic aspects by backscattered electron (BSE) imaging.

There was a distinct pattern of regional variation in bone density throughout the distal condyles of McIII. Bone density was greater in specimens fromGroup Ethan those fromGroup Cby CT, by radiographic density and by bone volume fraction as determined from backscattered electron images: the latter also showed that the most important change was in the increased amount of bone deposited within antecedent marrow space in cancellous tissue inGroup Ecompared withGroup C, with more extensive regional involvement in the highly loaded (distopalmar) aspects of the medial and lateral condyles. However, this space‐filling bone fraction had a lower degree of mineralisation than the prior bone tissue, showing that CT and radiography underestimate the resultant increased bone volume fraction. Stress fractures of the distal condyles of the McIII are common in Thoroughbred racehorses. We propose that excess stiffening within the condyles due to extensive new bone formation may lead to concentration of strain at the condylar grooves and incipient cracking through calcified cartilage and into the subchondral bone.