bluuebunny/crossref_metadata_2025 huggingface dataset:
Applying DNA barcoding for the study of geographical variation in host–parasitoid interactions
Authors: SANTOS ANA M. C. , BESNARD GUILLAUME , QUICKE DONALD L. J.
Published: June 2010

Studies on the biogeography of host–parasitoid interactions are scarce, mainly because of technical difficulties associated with rearing and species identification. DNA barcoding is increasingly recognized as a valuable tool for taxon identification, allowing to link different life history stages of a species. We evaluate the usefulness of a protocol based on cytochrome oxidase I (COI) sequencing for the study of geographical variation of host–parasitoid interactions. Larvae ofAcroclita subsequana(Lepidoptera: Tortricidae) were collected in Macaronesia and dissected to search for parasitoid larvae. Both hosts and parasitoids were sequenced and assigned to molecular operational taxonomic units (MOTUs) based on pairwise genetic distances, tree‐based and similarity‐based methods. Hosts were grouped into six MOTUs, usually with an allopatric distribution, while parasitoids clustered into 12 MOTUs, each of which was mostly found attacking a single host MOTU. Available COI sequence databases failed to provide identification to species level for these MOTUs. Three challenges related to the applicability of DNA barcoding in this type of studies are identified and discussed: (i) more suitable primers need to be developed for both parasitoids and hosts; (ii) the most commonly used approaches for inferring MOTUs have different limitations (e.g. arbitrary nature of defining a threshold to separate MOTUs) and need to be improved or replaced by other techniques; and (iii) for the identification of MOTUs, it is imperative to increase the range of sequenced taxa in the currently available reference databases. Finally, in spite of these difficulties, we discuss how DNA barcoding will help ecological and biogeographical studies of host–parasitoid interactions.
Evaluation of large‐scale dissemination of Nosema ceranae spores by European bee‐eaters Merops apiaster
Authors: Valera F. , Martín‐Hernández R. , Higes M.
Published: June 2010

Identification of transmission routes and of factors affecting the spatial positions of pathogens, hosts and vectors is basic to an adequate disease management. Nosema ceranae is a Microsporidian recently described as a parasite of Apis mellifera honeybees and is currently considered the aetiological agent of an emergent illness named nosemosis type C. In this article we evaluate the role of a bird species, the European bee‐eater, Merops apiaster, as a large‐scale dispersive agent of N. ceranae. We found a high prevalence of viable spores of N. ceranae in pellets regurgitated by bee‐eaters in different locations in the Iberian Peninsula, Central Europe and central Asia. In contrast, spores of Nosema apis, considered till recently the most common microsporidium infecting honeybees, were detected in a single locality and Nosema bombi spores were not noticed. Since non‐viable spores were also found in bee‐eater nests from different locations, this bird species could also reduce the fraction of infected insects by withdrawing pathogens from the colonies. We conclude that bee‐eater mobility and migration may have played an important role in the transmission of the pathogen N. ceranae.
Quantification of nitrogenase in Trichodesmium IMS 101: implications for iron limitation of nitrogen fixation in the ocean
Authors: Whittaker Sherrie , Bidle Kay D. , Kustka Adam B. , Falkowski Paul G.
Published: June 2010

Iron is widely thought to limit nitrogen fixation in the open, oligotrophic ocean due to the low solubility of Fe in oxic seawater and the high Fe demand for the nitrogenase holozyme. However, empirical evidence for Fe limitation of field populations of Trichodesmium based on either incubation experiments or molecular and physiological indicators has not quantitatively related Fe supply to the cellular Fe quotas for nitrogenase. Rather, the Fe required for N2 fixation has been inferred from in vivo catalytic activity. Using a pet14b expression vector, we cloned the nif H gene (encoding the Fe‐protein, which contains 4Fe atoms per subunit) from Trichodesmium IMS 101, and purified the His‐tagged apoprotein with which we derived a primary standard based on quantitative Western blots. Using a standard curve derived from the cloned Trichodesmium Fe apoprotein, we measured the absolute abundance of the Fe‐protein in iron‐replete cultures of this marine diazotroph. At peak expression, we calculate 0.04 mg nitrogenase mg−1 C. Assuming a conservative stoichiometry of two Fe‐protein subunits per MoFe protein (which contains 15 Fe atoms per subunit, or a total of 38 atoms of Fe per holozyme), we estimate 236 µmol Fe is bound to nitrogenase per mol cellular C. This estimate is about 10 times greater than the Fe previously calculated to support diazotrophic growth under these conditions. Our results suggest that under bloom conditions in the subtropical North Atlantic and North Pacific, as much as ∼2.22 and 0.06 µmol m−3 of Fe is bound to Trichodesmium nitrogenase respectively. Such a high quota represents between ∼50% and > 100% summer‐time average particulate Fe in surface waters, suggesting the importance of this taxon for the retention and biogeochemical cycling of Fe. Moderate growth (0.10 day−1) towards the end of these blooms would require a vertical flux as high as ∼23 µmol Fe day−1 m−2 into the mixed layer.
Physiological versus clinical consequences of left recurrent laryngeal neuropathy (LRLN)
Authors: SEEHERMAN H. J. , EHRLICH PAULA J. , MORRIS ELISABETH
Published: June 2010

The clinical implications of ventilatory alterations induced by left recurrent laryngeal neuropathy (LRLN) are reduced performance due to increased metabolic requirements for breathing and a reduction in peak aerobic power (V̇O2peak). To test this hypothesis, the metabolic cost of locomotion (MCL) and peak aerobic power (V̇O2peak) were measured in 4 non racing crossbred horses (low V̇O2peak) with reversibly induced LRLN using an incremental treadmill exercise test. Reversible LRLN was achieved with regional anaesthesia. These results were compared to previous measurements in 4 Thoroughbred racehorses (high V̇O2peak, Ehrlichet al.1993). No significant difference in MCL (based on V̇O2and venous lactate) was found in either group of horses at exercise intensities where V̇O2< V̇O2peak(<9 m/s). Peak aerobic power decreased by 15.3% (140.0 ± 3.2 vs. 165.3 ± 3.4 ml/kg/min ± s.e., in the Thoroughbred racehorses (high V̇O2peak) with induced LRLN but not in the non racing horses with lower V̇O2peak(135.0 ± 4.5 ml/kg/min ± s.e. The results of these 2 studies indicate that alterations in ventilation due to LRLN cause a significant reduction in V̇O2peakonly in horses with high V̇O2peak. At exercise intensities where V̇O2< V̇O2peak, MCL was not increased in either group of horses despite ventilatory alterations induced by LRLN.
Effect of head position on upper airway function in exercising horses
Authors: PETSCHE V. M. , DERKSEN F. J. , BERNEY C. E. , ROBINSON N. E.
Published: June 2010

The objective of the present study was to determine the effect of head and neck position on upper airway flow mechanics in exercising horses. Five Standardbred horses (452 ± 16.5 kg bwt; 4.7 ± 0.9 years [mean ± s.e.]) were exercised at 75% (Period A) and at 100% of maximal heart rate (Period B) with head and neck unrestrained, extended, or flexed. Airflow was measured using a facemask mounted pneumotachograph, while tracheal pressure during inhalation and exhalation (PUIand PUE) was measured using a nasotracheal catheter. With head and neck unrestrained, PUI, PUE, inspiratory and expiratory impedance (ZI, ZE), respiratory frequency (f) and indices describing the tidal breathing flow‐volume loops (TBFVLs) were similar to those previously reported. There were no significant changes in the extended position, except that expiratory time (Te) and ratio of peak expiratory flow and peak inspiratory flow (PEF/PIF) were significantly increased inPeriods AandB, respectively. In contrast, in the flexed position, ZIwas significantly increased inPeriod B.Also, inspiratory flow at 50% of tidal volume (IF50) was significantly decreased, and PEF/PIF and EF50/IF50were significantly increased. At period A, PUIwas increased and Te was prolonged. We conclude that during strenuous exercise head and neck extension has little effect on upper airway flow mechanics, but that head and neck flexion causes upper airway obstruction.
Ventilatory responses of horses to prolonged submaximal exercise
Authors: BAYLY W. , II H. SCHOTT , SLOCOMBE R.
Published: June 2010

While prolonged submaximal exercise is associated with an increase in core body temperature, the role of ventilation in the dissipation of this heat load is unclear. We examined airway mechanics in 5 horses exercising on a treadmill at 40% V̇O2maxfor 60 min or until fatigued, in order to study the ventilatory response to prolonged low intensity exercise. Respiratory tract mechanics, pH and arterial blood gases were recorded at rest and at regular intervals during exercise. Mean ± s.d. run time was 51.7 ± 5.9 min. No changes in ventilatory mechanics were seen in the first 12–15 min of exercise. Mean breathing frequency (fb) did not change during the test (109 ± 11), however, tidal volume (VT) and fbvaried considerably in individual horses over the course of the run. Some animals freely interchanged their breathing pattern between shallow tachypnoea and regular tidal breathing with fbranging from 76 to 171. Minute ventilation was not affected by breathing pattern but increased from 935 ± 119 l/min after 12–15 min to 1365 ± 343 l/min at the end of exercise. This was associated with a rise in pulmonary arterial blood temperature (BT) from 39.2 ± 0.2°C to 41.8 ± 0.4°C and an increase in work of breathing (Wrm) from 214 ± 30 to 475 ± 122 kg/cm. Wrm/min/l and kg·min increased 1.98‐, 1.28‐ and 1.87‐fold, respectively, in the same period. VTand each expression of Wrmwere logarithmically correlated with BT. PCO2decreased from 41.2 ± 1.7 Torr after 12–15 min to 30.6 ± 1.3 Torr after 57–60 min, while pH increased from 7.43 ± 0.03 to 7.56 ± 0.03 in the same period. We conclude that while the thermoregulatory role of the equine respiratory system may be unclear, horses mount a concerted hyperventilatory response during prolonged submaximal exercise. This response may be associated with rises in core temperature and intermittent tachypnoea, is characterised by increases in Wrmand may be physiologically costly and inefficient.
Assessment of anaerobic capacity using maximal accumulated oxygen deficit in fit Thoroughbreds
Authors: EATON M. D. , ROSE R. J. , EVANS D. L. , HODGSON D. R.
Published: June 2010

Twenty‐three Thoroughbred racehorses that were presented for a standard incremental exercise test also performed a test at an intensity equivalent to 115% V̇O2max in an effort to evaluate their anaerobic capacity by measuring the maximal accumulated oxygen deficit (MAOD). Submaximal V̇O2 values for speeds 3 to 10 m/s and V̇O2max were determined for horses exercising on a treadmill inclined at a 10% slope. An individual regression equation of speed and V̇O2 was used to calculate the speed for each horse to exercise at 115% V̇O2max and the energy demand for exercise at this intensity. The horses underwent a warm‐up period consisting of 5 min at 50% V̇O2max followed by walking for 5 min at 1.5 m/s. The treadmill was then acclerated as rapidly as possible until a speed of 115% V̇O2max was attained. During the test, expired gas samples were collected at 0, 15, 30, 45, 60 s and every 30 s until fatigue. MAOD was calculated by subtracting the measured oxygen uptake from the calculated oxygen demand. A 5 min post exercise blood sample was collected for measurement of plasma [lactate]. The MAOD values ranged from 36 to 94 mlO2 equivalents/kg and the V̇O2max values ranged from 128 to 170 ml/kg/min. The mean ± s.e. MAOD values were 59 ± 3 mlO2 equivalents/kg and mean V̇O2max was 146 ± 2 ml/kg/min. Mean plasma [lactate] was 23.0 ± 1.2 mmol/l. MAOD was weakly correlated with V̇O2max (r = 0.514, P < 0.05), but was not correlated with run time, plasma lactate or treadmill work. The test of MAOD was suitable for use during clinical exercise testing.
Flow cytometric studies of equine phagocytes following strenuous exercise
Authors: ADAMSON ELISABETH J. , SLOCOMBE R. F.
Published: June 2010

The objective of this study was to determine if strenuous exercise in unconditioned horses impaired function of neutrophils and alveolar macrophages. Flow cytometry was used to assess the effects of a single bout of strenuous exercise on these cells. Bronchoalveolar lavage and venous blood sampling were performed 30 min, 1 and 5 days after exercise. Exercise consisted of 2 min at 2,4 and 6 m/s and then 1 min at 1 m/s incremental speeds until exhaustion, on a level treadmill. Intracellular oxidation of the fluorochrome dye DCFH‐DA was stimulated by PMA and detected by a flow cytometer. Size and granularity of the 2 cell preparations were also measured. The respiratory burst induced in granulocytes was significantly inhibited 30 min after exercise (480 ± 182) compared to that prior to exercise (2359 ± 456). Inhibition at 1 and 5 days after exercise was less than at 30 min and did not differ significantly from either control values. No change in size or granularity was seen as a result of exercise. The alveolar macrophage population remained unchanged in size, granularity and fluorescent responses following exercise. Several cell samples taken before exercise exhibited peripheral blood eosinophilia. In these samples, granulocyte size was markedly reduced and DCFH‐DA oxidation was depressed; viability did not alter. This study suggests that strenuous exercise impairs the respiratory burst of granulocytes for several days. Other factors associated with peripheral eosinophilia also have suppressive effects on granulocytes.
Effects of low intensity training on gas exchange at the start of exercise
Authors: BELLENGER SARAH , DAVIE A. J. , EVANS D. L. , HODGSON D. R. , ROSE R. J.
Published: June 2010

We tested the hypothesis that training would result in more rapid increase in V̇O2 and V̇CO2 following the onset of submaximal exercise. Six Standardbred horses were used and trained at submaximal intensities for 5 weeks. Horses were trained 6 days per week on an inclined treadmill (10% slope) at intensities between 40 and 70% V̇CO2max. At the onset of training horses ran 2600 m/day which progressively increased to 4500 m/day by week 5. Testing was carried out before training and after weeks 3 and 5 of training. The test involved exercise at 2 speeds, 4 m/s and 8 m/s, both for 3 min with one h recovery between the 2 speeds. All horses performed at both speeds but the initial speed was randomly allocated. An open flow gas collection system was used to measure V̇O2 and V̇CO2 every 15 s for the first min of exercise and every 30 s thereafter. After 5 weeks training, mean body weight and V̇O2max (mean ± s.e.) of the group had altered from 433 ± 5 kg to 430 ± 8 kg (P > 0.05) and from 104 ± 5 ml/kg/bwt/min to 116 ± 6 ml/kg/bwt/min (P < 0.05), respectively. There were no significant training effects on the rate of change of V̇O2 or V̇CO2 at either of the test speeds. By 45 s, the V̇O2 and V̇CO2 values had reached 85 to 95% of mean steady state values at both intensities of exercise. In general, steady state V̇O2 and V̇CO2 values were evident by 60 s of exercise. We conclude that horses have rapid increases in gas exchange at the start of exercise and these are not influenced by low intensity training.
Effects of exercise intensity and training on bronchoalveolar lavage cytology
Authors: McKANE S. A. , ROSE R. J.
Published: June 2010

Although bronchoalveolar lavage (BAL) has become a commonly used technique for evaluation of pulmonary cytology and there have been many reports on horses at rest and in race training, there have ben no longitudinal studies where cytological results have been assessed during a training programme which involved increases in training intensity. In this study, 10 Thoroughbred horses were trained on a treadmill for a period of 12 weeks and were divided into 2 groups, one group (FAST) being trained at intensities to produce whole blood lactate concentrations in the range 4–8 mmol/l while the other group (SLOW) were trained at half the intensity of the FAST group. The training speeds for the FAST group ranged from 8–11 m/s whereas that for the slow group ranged from 3–6 m/s. Horses were trained for 6 days/week over daily distances of 1000–3600 m. Bronchoalveolar lavage samples were collected from each horse during weeks 1, 3, 6, 8, 10 and 12. The BAL samples were analysed and compared with respect to changes in cytology occurring throughout the period of training. The results of the study indicated that intensity and duration of exercise may have an effect on the development and severity of exercise induced pulmonary haemorrhage (EIPH), as determined by the absolute count and the percentage of erythrocytes returned in a BAL sample. This appears to be especially true when training at high intensities. However, the low levels of EIPH detected in the horses were not sufficienttocause a measurable loss of exercise performance or lowering of the horses' maximal oxygen uptake during exercise. Low intensity training was noted to have very little effect on the observed BAL cytology.
Tracheal pressure in horses with signs of dorsal displacement of the soft palate
Authors: ROETHLISBERGER‐HOLM KARIN
Published: June 2010

Among the functional disorders of the upper respiratory tract, dorsal displacement of the soft palate (DDSP) is still a major diagnostic challenge. In this study, measurements of tracheal pressure were made in exercising horses with clinical signs of DDSP. Tracheal pressure was recorded via a percutaneously inserted tracheal catheter during exercise on a treadmill with an inclination of 6.25°, at speeds up to 9 m/s. Five horses with clinical signs of DDSP were compared to 20 earlier studied normal horses. In horses with signs of DDSP the tracheal pressure curve had a characteristic appearance. There were a number of short‐duration pressure peaks over a prolonged expiratory phase and an elevated peak expiratory pressure. The inspiratory pressure was within normal limits. These findings support the hypothesis that obstruction of the air passage in DDSP occurs mainly during expiration and the short peaks of the expiratory pressure curve may reflect the vibrations of the edge of the soft palate.
Pleural pressure changes during exercise do not affect measurement of mean pulmonary vascular pressures
Authors: SINHA A. K. , HAKIM T. S. , GLEED R. D. , DOBSON A.
Published: June 2010

This study was designed to evaluate the influence of pleural pressure on mean pulmonary vascular pressures in exercising horses. Pulmonary artery (Pa), pulmonary wedge (Pw) and oesophageal pressures (Pes) were measured with transducer tip catheters in 6 Standardbred horses at rest and during treadmill exercise at 75, 90 and 100% of maximal heart rate. Oesophageal pressure (Pes) measurements were used to estimate pleural pressure. Vascular pressures were determined in 4 ways: 1) mean transmural vascular pressure (Ptm) at Pesequal to resting end expiratory pressure; 2) mean Ptmat Pesequal to mean Pesfor the data collection period; 3) mean Ptmwithout selection of specific data points and 4) mean pulmonary vascular pressure relative to atmospheric pressure (conventional method). Despite large fluctuations associated with breathing, mean Pesduring exercise remained close to zero, suggesting that pleural pressure fluctuates equally about zero. The swings in Peswere associated with approximately equal swings in vascular pressure so that, despite the marked fluctuations, mean Paand Pwdetermined with the 4 methods were not significantly different. The results indicate that during exercise it is valid to report mean pulmonary vascular pressures without accounting for the fluctuations in pleural pressure.
Heart and spleen mass related to blood parameter changes after epinephrine injection
Authors: HANSON CHRISTINE M. , KLINE K. H. , FOREMAN J. H. , FREY L. P. , COOPER S. M.
Published: June 2010

The purpose of this study was to determine if splenic weight is correlated to changes in blood volume, haematocrit and haemoglobin concentration after epinephrine injection in horses. Ten mares, 5 racing type and 5 draft type, all over age 5 years were studied. Differences in plasma volume (PV), red cell volume (RCV), total blood volume (TBV) and venous haematocrit (PCV) were maximised by xylazine and epinephrine treatments to either sequester or mobilise the splenic RCV. Plasma volume was determined using an Evans Blue Dye (EBD) dilution technique, then used to calculate TBV and RCV. Horses were killed by captive bolt gun and exsanguination, and heart (HW) and spleen weights (SW) were recorded and expressed as a percentage of body weight (BW). Significant differences between breed types were found for changes in RCV and PCV between treatments. Analysis of variance found significant differences between breed types in HW/BW and SW/BW ratios. Regression analysis demonstrated a positive relationship between the change in RCV between treatments and SW/BW with significant differences (P < 0.01) between breed types in this relationship. There was no relationship between changes in RCV or PCV and HW/BW.
Kinematic response to a 70 day training period in trotting Dutch Warmbloods
Authors: BACK W. , HARTMAN W. , SCHAMHARDT H. C. , BRUIN G. , BARNEVELD A.
Published: June 2010

To study the influence of training on the equine locomotor apparatus, the kinematics of 24 almost two‐and‐a‐half‐year‐old Dutch Warmbloods were recorded on a treadmill at the trot (4 m/s) using a modified CODA‐3 apparatus before and after a period of 70 days. In that period, 12 horses of the group were trained for dressage and jumping, while the other 12 were sent to pasture day and night. After 70 days, the hindlimb of the trained horses showed a decreased stance duration, less limb flexion and it reached its maximal protraction earlier in the stride. The stride duration remained the same in the trained horses, while the protraction and retraction range of the forelimb decreased in this group. In the pastured group, however, the horses increased their total range of forelimb movement in the sagittal plane and had a longer swing and stride duration. These results indicate that the definition of ‘training’ is rather relative. The response in the trained group was in agreement with the observation that the majority of horses from this group were trotting with impulsion ‘on the bit’. The pastured group was trotting in a more relaxed way with a longer stride duration and thus a lower stride frequency. In conclusion, this study proved that horses show different responses in their locomotor apparatus depending on the ‘training’ regime received. Using modern gait analysis equipment these differences could be evaluated objectively.
Kinematics of the distal forelimb during the stance phase in the fast trotting Standardbred
Authors: JOHNSTON C. , ROEPSTORFF L. , DREVEMO S. , RONÉUS N.
Published: June 2010

Fast‐trotting Standardbred horses were filmed along a straight on an oval dirt track. Five consecutive stance phases were analysed to describe the plantar kinematics of the distal forelimb. Rapid changes in the geometry of the distal forelimb occurred during the early stance phase. The hoof segment was initially compressed vertically and moved in the direction of the horse. In general, the angular displacement of the fetlock joint was a smooth curve with 2 specific deviations in the early stance phase. The deviations are suggested to be related to the braking of the hoof and activation of the flexor muscles of the distal forelimb. A rotational dissociation occurred between the antebrachial and metacarpal segments due to a delay in braking caused by the carpus which preceded the maximal overextension of the carpus. The early stance phase changes in the distal forelimb suggest rapid changes in the internal forces of the limb and should be of importance to the orthopaedic health of Standardbred trotters.
Simple airflow direction and footfall sensors for use in equine exercise studies
Authors: YOUNG S. , STÄMPFLI H. , GEOR R. , McCUTCHEON LAURA J. , PRINGLE J.
Published: June 2010

Two durable, inexpensive and non‐invasive sensors for detecting airflow direction and footfall in exercising horses were developed. The airflow sensor measured temperature of the gas at the nostrils using a copper/constantan thermocouple. The response time of the thermocouple unit, the time for the signal to change from 10% to 90% of its final value, was 260 ms in forced air. The tip of the thermocouple was held just inside the false nostril by a small wire frame. The sensor did not interfere with placement of face masks and the addition of the mounting frame slightly decreased response time of the sensor to 208 ms. The footfall sensor was a simple accelerometer, using the contact arm of an electrical relay as a spring/mass unit. Bending of the metal strip was recorded using a strain gauge. The response of the accelerometer was highly under‐damped when attached to a rigid surface (resonant frequency 117 Hz, quality factor (Q) 171) but attaching it to the hoof with adhesive foam increased the damping considerably. Both sensors were used in a study of Standardbred horses exercising maximally on a treadmill. Air temperature at the nostril changed from ambient on inspiration to about 35°C on expiration and each leading hoof strike produced a burst of signal from the accelerometer. The sensors may be useful in studies that examine respiration, stride rate and respiratory‐locomotor coupling in exercising horses.
Effects of post exercise activity on recovery from maximal exercise
Authors: LOVELL D. K. , ROSE R. J.
Published: June 2010

We determined the effect of post exercise activity on recovery from maximal exercise. Five Standardbred horses were exercised on an inclined treadmill (+10% slope) for 2 min at 2.5 m/s followed by 2 min at 12.5 m/s (∼110% V̇O2max). They had one of 3 recovery regimens: standing on the treadmill (A), trotting at 4 m/s for 15 min followed by walking at 2 m/s for 15 min (B), or walking at 2 m/s for 30 min (C). Muscle biopsies from the m. gluteus medius and jugular blood for blood lactate determination were collected, before and after exercise and at 3, 5, 10, 15, 20 and 30 min recovery. Ten minutes after exercise, heart rate was significantly (P<0.05) higher with recoveries B and C than recovery A, but there were no differences at 20 or 30 min following exercise. Both muscle and rectal temperatures were significantly (P<0.01) lower with recovery A compared with recoveries B and C. The type of recovery had no influence on the rate of change of [ATP] or [G‐6‐P]. The rate of decrease in plasma and muscle [lactate] was significantly faster with recovery B than A (P<0.05). Creatine phosphate increased (P<0.05) at a faster rate with recoveries B and C than A. We conclude that ‘warm‐down’ periods enhance clearance of lactate from skeletal muscle and that lactate may be utilised as a substrate by muscle during recovery from exercise.
Effect of elevated plasma FFA on fat utilisation during low intensity exercise
Authors: ORME C. E. , HARRIS R. C. , MARLIN D. J.
Published: June 2010

The aim of the present study was to evaluate the capacity of the horse, during low intensity exercise, to increase the contribution of fat oxidation to energy production as a result of a pre‐exercise elevation of triglyceride derived plasma FFA. Seven Thoroughbred horses were exercised for 91 min (3.2 m/s for 60 min, 13.4 ± 2.9% V̇O2max) during 2 randomised experimental sessions (test, T and control, C). Prior to the test session, plasma FFA were elevated using a combination of a heparinoid type substance (pentosan polysulphate, 1.3 mg/kg bwt) and a triglyceride emulsion (Iverlip 20; 0.4 g/kg bwt). Mean pre‐exercise plasma FFA and triglyceride concentrations were 903.9 ± 275.0 and 810.2 ± 169.6 μmol/l for the test session and 465.5 ± 266.0 and 158.4 ± 64.5 μmol/l for the control session, respectively. Total lipase activity was significantly increased at rest after pentosan polysulphate and Iverlip administration and throughout exercise during the test session. Respiratory exchange ratio (RER) was lower in 5 out of 7 horses and plasma glucose concentration was higher in 4 of these 5 horses during the test exercise session. These results suggest that an elevation of plasma FFA concentration prior to exercise results in an increase in the utilisation of fat, during subsequent low intensity exercise, in a proportion of horses. This effect, however, is probably influenced by individual biological and metabolic variation in the response to exercise and may depend upon the individual's inherent ability to utilise fat.
Limitations to performance caused by skeletal muscle enzyme deficiencies
Authors: VALBERG STEPHANIE J. , JONES J. H. , SMITH BARBARA L. , SOMMERVILLE B.
Published: June 2010

Recently, 2 new enzyme deficiencies of equine skeletal muscle have been identified, involving either mitochondrial respiration or glycolysis. We hypothesised that in these unique horses, maximum oxygen consumption (V̇O2max) would not be limited by oxygen transport but rather by oxygen utilisation and substrate metabolism, respectively. To test this hypothesis, an Arabian mare with Complex I deficiency (OXID) and 2 half‐sibling Quarter Horses with a polysaccharide storage myopathy (GLY1 and GLY2) were accommodated to run at maximal speed on a treadmill. These horses and 5 healthy Thoroughbred horses each performed 2 identical exercise tests consisting of 6 min submaximal exercise and 2 min at their maximal speed. The OXID horse fatigued at 6 m/s with a markedly low V̇O2max (20% of controls), a low maximum total power output (25% of controls) with a high contribution of net anaerobic power (38% compared to 24% for controls). The GLY horses developed a stiff gait and fatigued with a low V̇O2max (50–65 % of controls), a low maximum total power (50–60% of controls) but with a low contribution of net anaerobic power (18% vs. controls 24%). The rate of lactate accumulation at maximal speeds was approximately 30–50% lower than for controls. It appeared that mitochondrial oxidative capacity severely limited aerobic performance in the OXID horse and substrate limitation within the Embden Myerhof pathway limited both aerobic and anaerobic power output in the GLY horses. We conclude that in some horses, skeletal muscle oxidative or glycolytic capacity may limit maximum aerobic performance.
Carnosine and taurine contents of type I, IIA and IIB fibres in the middle gluteal muscle
Authors: DUNNETT M. , HARRIS R. C.
Published: June 2010

Thoroughbred racing involves periods of intense exercise above the anaerobic threshold, characterised by H+ ion accumulation in muscle. Progressive intracellular acidosis may be a primary cause of local muscle fatigue. Carnosine is quantitatively the most important buffer in equine skeletal muscle with estimated contents 3–5‐fold greater in type II compared with type I fibres. Taurine is believed to be concentrated in type I fibres. In the present study we have measured carnosine and taurine contents directly within individual fibres. Seven samples were collected from the middle gluteal muscle of 5 horses at post mortem. Fibres were dissected from freeze‐dried tissue, weighed and characterised as types I, IIA or IIB by histochemistry. Carnosine and taurine contents were determined by HPLC. Mean (± s.d.) carnosine contents of type I, IIA and IIB fibres were 24.9 ± 4.4 mmol/kg dry muscle (d.m.), 94.8 ± 6.8 mmol/kg d.m. and 104.3 ± 11.9 mmol/kg d.m. respectively. Mean (± s.d.) taurine contents of type I, IIA and IIB fibres were 54.3 ± 8.3 mmol/kg d.m., 2.8 ± 2.1 mmol/kg d.m. and 1.8 ± 1.9 mmol/kg d.m. respectively. The results agree with previous estimates. Higher carnosine contents in type II fibres emphasise the importance of carnosine to intramuscular acid‐base regulation. A specific role for taurine in type I fibres is unclear. Owing to the differential distribution in muscle fibres of carnosine and taurine, their appearance in plasma may be useful in diagnosing types I or II fibre damage.
The effect of moderate exercise on equine muscle satellite cells in vitro
Authors: GREENE ELIZABETH A. , BALCH S. G. , RAUB R. H. , GAUGHN E.
Published: June 2010

Twelve weanling Quarter Horses were divided randomly into 2 groups; exercised (EX) and non‐exercised (NONEX). The EX horses were divided randomly into 2 groups subjected to either a 15‐day or 30‐day exercise protocol and weanlings were exercised at a brisk trot (3 m/s) on a high speed treadmill. Muscle satellite cells were obtained by surgical biopsy from the biceps femoris at the conclusion of exercise protocols. Time course studies were used to examine the main effects of exercise on proliferation and differentiation of equine satellite cells (ESC) in vitro. No differences occurred between proliferation and differentiation of cells from 15‐ or 30‐day EX and NONEX treatments. In a second experiment, the ability of serum from EX or NONEX horses to stimulate proliferation or differentiation of ESC in vitro was examined. Serum had a significant effect on both proliferation and differentiation. During Days 3 and 5 in culture, serum from EX weanling horses increased (P<0.005) total cell numbers; however, after 7 days, no differences (P>0.10) existed between serum sources. From Days 3–7, satellite cells cultured in serum from EX horses had greater (P<0.005) per cent fusion than cells cultured in serum from NONEX weanling horses. Origin of satellite cell cultures (EX or NONEX) caused no differences. A constituent seems to be present in the serum from EX that is capable of stimulating increased levels of proliferation and differentiation of ESC.
Exercise induced purine nucleotide degradation and changes in myocellular protein release
Authors: RÄSÄNEN LEENA A.
Published: June 2010

Xanthine oxidase has been claimed to produce tissue damaging oxygen free radicals during purine nucleotide degradation. The aim of this study was to evaluate whether xanthine oxidase (XO) activity is present in horse plasma and whether it is associated with the post exercise release of muscular proteins into plasma. Purine nucleotide degradation was measured as the accumulation of reaction end products, uric acid and allantoin, and activities of aspartate aminotransferase (AST), creatine kinase (CK), carbonic anhydrase (CA) and the concentration of myoglobin in plasma were measured as indicators of increased sarcolemmal permeability after a standardised submaximal exercise test (SET) on a high speed treadmill and after maximal exercise (trotting races). The activity of XO in plasma was significantly elevated up to 5 min after the SET and correlated positively with the activity of CK measured 1 h after exercise, but not with the concentrations of uric acid or allantoin. After the trotting races, concentration of myoglobin and activity of CK peaked within 4 h after exercise. No correlation was found between CK and the concentrations of uric acid and allantoin. CA activity did not change significantly in any of the samples. These findings suggest that XO, both in plasma and in endothelial cells, may contribute to the formation of free radicals and therefore to the genesis of exercise induced increase in the sarcolemmal permeability.
Effects of creatine supplementation in the Thoroughbred horse
Authors: SEWELL D. A. , HARRIS R. C.
Published: June 2010

The present study was undertaken to examine the absorption of creatine (Cr) by the horse and, if so, whether this results in an uptake of Cr into muscle. The timecourse for the appearance of a single dose of creatine monohydrate (Cr.H2O), given by nasogastric intubation, in plasma was investigated in 4 horses. Individual resting plasma [Cr] ranged from 8 μmol/1 to 103 μmol/1. Mean post intubation plasma concentrations showed a modest increase reaching a peak after 6 h. At various times post intubation the change from rest was statistically significant. The effect of 13 days feeding of 0.15g/kg body mass/day of Cr.H2O on muscle [TCr] was studied in 4 horses. Supplementation had no effect upon muscle [TCr] (pre‐ vs. post supplementation: 104 ± 4 vs. 98 ± 14 mmol/kg dry muscle). There was no change either in the resting muscle [ATP] (pre‐ vs. post supplementation: 21.2 ± 1.0 vs. 20.2 ± 1.9 mmol/kg dry muscle) or the [TCr]/[ATP] ratio.
Effect of conditioning and exercise type on serum creatine kinase and aspartate aminotransferase activity
Authors: SICILIANO P. D. , LAWRENCE L. M. , DANIELSEN KRISTIN , POWELL DEBRA M. , THOMPSON K. N.
Published: June 2010

In the first study, 5 mature, unconditioned, Thoroughbred geldings performed an initial submaximal exercise test (UC) prior to any conditioning and a final test (C) following 8 weeks conditioning. Serum creatine kinase (CK) and aspartate aminotransferase (AST) activity were measured before and for 72 h after exercise. Plasma lactate concentration [La−] was used as an indicator of exercise conditioning. Serum CK and AST activity remained increased above pre‐exercise levels from 0–24 h and 0–8 h post exercise, respectively. There was a time by conditioning interaction for AST, CK and plasma [La−] resulting in an attenuated response of each variable following exercise test C as compared to following exercise test UC. These results indicate that submaximal exercise can elevate serum AST and CK and that conditioning can attenuate these changes.

A second study using 8 mature Thoroughbred horses was conducted to evaluate the effect of 2 different types of exercise, short term high intensity (STHI) and repeated submaximal exercise (RS) on serum AST and CK activities. Serum AST and CK activities during the post exercise period were higher in response to the RS test compared to the STHI test.
Effects of NaCI supplementation before exercise on metabolism of water and electrolytes
Authors: COENEN M. , MEYER H. , STEINBRENNER B.
Published: June 2010

Four horses were exercised for 2 h on a treadmill at up to 200 m/min 4 h after feeding. The trial included 3 treatments, control (A) and electrolyte supplementation provided either in the diet at the morning feeding (B) or 1 h before start of exercise (C). The horses were fed 2 meals/day of hay and concentrate (6.5 g dry matter, 13.8 mg Na, 66.6 mg K and 54.2 mg Cl/kg bwt per meal). The supplement was a mixture of grass meal (47.6%), sugar beet syrup (33.3%) and NaCl (19.1%); additional intake: Na 79.7, K 15.5 and Cl 165.6 mg/kg bwt. Hourly urine and blood samples were taken.

Water intake and renal water excretion were significantly influenced by supplementary feeding (intake: A 35.5, B 49.9, C 55.6 ml/kg bwt/12 h; excretion: A 9.47, B 15.34, C 7.92 ml/kg bwt/12 h). The urinary Na and Cl excretion was significantly higher in treatment B (Na 24, Cl 55 mg/kg bwt/12 h) and C (Na 12, Cl 44 mg/kg bwt/12 h) as compared to A (Na 5, Cl 16.5 mg/kg bwt/12 h). Renal K output was less influenced by the different treatments, A 43, B and C 61 mg/kg bwt/12 h. However, the renal Na and Cl excretion was lower in relation to intake when horses received the supplement. In these cases, losses of water, Na and Cl via sweat were compensated for at the end of exercise and a positive balance therefore maintained 12 h after feeding. The total plasma protein concentration increased during exercise, indicating a reduction in plasma volume. The Na and K concentrations in plasma during exercise showed minor changes whereas the Cl concentrations decreased significantly by 2.6 (A), 4.0 (B) and 1.4 (C) mmol/l. Changes in plasma Na and Cl in treatments B and C occurred at constant higher levels than in treatment A.

The results suggest a positive impact of NaCl suplementation on water and electrolyte metabolism in exercised horses. The increased water intake indicates that supplementary salt intake is more effective about 4 h than 1 h before exercise.
Effects of oral fluid on cardiorespiratory and metabolic responses to prolonged exercise
Authors: LEÓN L. A. SOSA , DAVIE A. J. , HODGSON D. R. , EVANS D. L. , ROSE R. J.
Published: June 2010

Administration of oral fluids prior to exercise may provide a fluid ‘buffer’ supporting cardiorespiratory and thermoregulatory function during prolonged exercise. Six Standardbred horses, previously acclimatised to a treadmill and a respiratory gas collection mask, were used in a crossover study and were given ∼17.5 litres hypotonic commercial electrolyte mixture via a nasogastric tube, 90 min before exercise. Total fluid was equivalent to 4% bwt, administered in 3 equal doses, 20 min apart, the last 50 min before exercise resulting in a mean ± s.e. pre‐exercise plasma total protein (TPP) of 57.6 ± 0.6 g/l, compared with 63.5 ± 0.5 g/l (P < 0.01) when no fluid was given. One week later, each horse received the alternate treatment. The exercise test consisted of 90 min at 30% V̇O2max with measurements taken throughout exercise. Exercise increased temperature, haematocrit, TPP, [glucose], [lactate] and pH and decreased plasma [K] and [Cl], respiratory exchange ratio and PaCO2. There was no effect of exercise duration on heart rate, cardiac output, stroke volume, V̇O2 V̇CO2, [HCO3] or PaO2. Fluid administration resulted in lower TPP, plasma [Cl], [HCO3] and [Na] during exercise. Although fluid administration before exercise did not improve cardiorespiratory and thermoregulatory function, the fluid treated group had a higher plasma volume which may be advantageous to horses exercising in hot and humid environments.
Effects of terrain, speed, temperature and distance on water and ion losses
Authors: ECKER GAYLE L. , LINDINGER M. I.
Published: June 2010

Factors contributing to water and ion losses due to sweating have not been well studied during prolonged exercise in horses. This study examined temperature (T; °C; range 6–32°C), distance (D; km; 48–161 km), speed (S; km/h; 8–19 km/h) and muddy terrain (M) as factors determining water and ion losses. Jugular venous blood samples (analysed for plasma ions and refractive index) and body mass (BM) were obtained from 176 endurance horses at 13 events at rest, mid‐ride and finish. Regression analysis determined correlations between losses of total body water (TBW) and extracellular (ECF) ions and the variables T, M, S and D. Losses of ECF ions and TBW were calculated assuming an ECF volume (ECFV) of 1 litre/5 kg BM. There were significant decreases in BM (range of means 2–7%) and ECFV (range of means 2–14%) at mid‐ride and finish; however, these were independent of the variables tested. Losses of Na+, K+, Cl−and Ca++were correlated with T, D, S and M. Inclusion of S in the model eliminated T and M as factors for Na+, Cl−and Ca++loss. Speed was not a predictor of K+loss. ECF ion losses at the mid‐ride were correlated to T, S, D and M. In conclusion, factors affecting ion losses at the finish, in descending order of importance, were speed (except for K+due to rapid intercompartmental shifts), muddy terrain, temperature, then distance (for Cl−). Using the data from the literature models were used to predict ECF ion losses in endurance events.
Plasma and erythrocyte ion concentrations during exercise in Arabian horses
Authors: FERRANTE PAMELA L. , TAYLOR LYNN E. , WILSON JUDY A. , KRONFELD D. S.
Published: June 2010

Six conditioned Arabian horses were subjected to an intermittent exercise test to examine alterations in plasma and erythrocyte ions during exercise. Haematocrit, erythrocyte haemoglobin concentration, plasma potassium [K+] and lactate [La−] concentrations increased and plasma sodium [Na+] and chloride [Cl−] concentrations decreased during exercise. Erythrocyte [K+] and [La−] increased and erythrocyte [Na+] decreased during exercise. When cell volume was held constant at resting values, potassium content of the cells was slightly greater than resting values; and sodium and chloride content decreased during exercise. Increased haematocrit in horses during exercise due to splenic contraction increases the erythrocyte membrane surface area and distribution space for blood ions. Movement of lactate into erythrocytes may modulate the increase in plasma [La−), maintaining the muscle to plasma gradient and facilitating the movement of lactate from muscle into plasma.
Plasma total CO2and electrolytes: diurnal changes and effects of adrenaline, doxapram, rebreathing and transport
Authors: SLOCOMBE R. F. , HUNTINGTON P. J. , LIND KAREN L. , VINE J. H.
Published: June 2010

Pre‐race testing for plasma bicarbonate is used in Australia to detect administration of large doses of bicarbonate or other alkalising agents. The rules specify upper limits for plasma TCO2from 35 to 37 mmol/l, depending on State. There has been considerable speculation about physiological factors that may increase plasma total CO2and lead to infringements of this rule. In order to address these purported influences, we measured body temperature (BT), heart rate (HR), haemoglobin concentration (Hb), packed cell volume (PCV), TCO2, potassium [K], sodium [Na], chloride [Cl] and breathing frequency (Fb) in 6 horses under the following conditions: rebreathing into a 3 litre bag for 90 s following respiratory stimulation with doxapram (0.5 mg/kg bwt i.v.); following excitement and during sweating induced by adrenaline (2.5 mg/kg bwt i.v.).

We also evaluated whether significant diurnal variation existed in plasma electrolytes. There was no diurnal variation in sodium but potassium and chloride peaked in the evening and were lowest at early morning. TCO2changes were also significant with peak values occurring before noon. Rebreathing produced transient marginal increases in TCO2and potassium, declines in chloride and no change in sodium. The rise in TCO2was from 29.6 ± 0.8 to 30.9 ± 1.4 mmol/l. Animals became markedly agitated by 90 s of rebreathing. Doxapram caused a 2‐fold increase in Fb, a small (<1 mmol/l) increase in TCO2, marginal increases in sodium and potassium, but no change in chloride. Adrenaline caused marked sweating and anxiety in all horses and led to increased HR, sodium, chloride, PCV and Hb, caused decreased TCO2(<2 mmol/l), decreased chloride and had no consistent effect on BT.

From these studies, we conclude that rebreathing, hyperpnoea induced by doxapram and sweating and excitement induced by adrenaline, in otherwise healthy horses, exerts only marginal effects on TCO2. Differences were significant for all measured electrolytes between horses, with magnitudes exceeding changes induced by experimental protocols. Mean TCO2for individual horses ranged from 26.5 ± 0.3 to 33.8 ± 0.2 mmol/l in the adrenaline trial with similar ranges in other studies.