Skeletal muscle fiber size in untrained and endurance-trained horses.

The mean area and minimal diameter of 3 histochemically determined myofiber types (1, 2A, and 2B; myosin ATPase in acid buffer) were calculated in middle gluteal muscle biopsy specimens from 62 stallions, 47 Andalusians and 15 Arabians, ranging in age from 6 to 12 years. Fourteen Andalusians and 7 Arabians were untrained, and the remainder were actively endurance-trained. The 6-month training schedules involved walking, slow trotting, and cantering. Fourteen Andalusians were moderately endurance-trained, whereas the other 19 Andalusians and 8 Arabians were strongly endurance-trained. Significant differences were not recorded between untrained and endurance-trained Arabians with respect to the area (type 1, 3,194 +/- 869 microns 2 and 3,150 +/- 370 microns 2; type 2A, 3,819 +/- 890 microns 2 and 3,380 +/- 356 microns 2; and type 2B, 4,872 +/- 962 microns 2 and 4,417 +/- 646 microns 2) or minimal diameter (type 1, 52.2 +/- 7.4 microns and 52.8 +/- 3.1 microns; type 2A, 58.1 +/- 6.7 microns and 55.0 +/- 2.8 microns; and type 2B, 65.3 +/- 6.4 microns and 63.4 +/- 4.3 microns) of the 3 fiber types, nor between untrained and endurance-trained Andalusians with respect to the area (untrained, 3,990 +/- 690 microns 2; moderately endurance-trained, 3,882 +/- 347 microns 2; and strongly endurance-trained, 3,758 +/- 510 microns 2) and minimal diameter (untrained, 58.1 +/- 4.7 microns; moderately endurance-trained, 59.7 +/- 2.7 microns; and strongly endurance-trained, 58.7 +/- 4.5 microns) of 2A fibers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative ergoespirometric adaptations to a treadmill exercise test in untrained show Andalusian and Arabian horses

Significant differences exist in the respiratory adaptation to exercise in different equine breeds. This research describes the ergoespirometric response to exercise of Andalusian (AN) and Arabian (A) horses, both selected according to morphological criteria. Thirteen untrained male horses (6 AN and 7 A) performed a treadmill exercise test (TET) with a slope of 6%, with workloads starting from 5 m/s and increasing 1 m/s every 3 min until the horses were not able to keep the required velocity. Tidal volume (TV), respiratory rate, minute ventilation (VE), oxygen uptake (VO2), carbon dioxide production, peak oxygen uptake (VO2peak), respiratory exchange ratio (RER), exercise time to fatigue (ETF) and respiratory aerobic threshold (RAT) were determined. AN horses presented higher TV and VE, whereas respiratory rate, VO2 and VCO2 were lower at the same velocities. RER was similar between breeds. ETF was longer in A horses (556.7 ± 66.5 in AN vs. 607.1 ± 71.1 s in A) and no significant differences were found in RAT (5.50 ± 0.50 in AN vs. 5.86 ± 1.07 m/s in A). In summary, despite the more intense ventilatory response to exercise at the same velocity, AN horses had lower VO2. The AN horse develops a more intense ventilatory response to fixed velocities than the A horse and it could be interesting to clarify the role of the locomotion characteristics in this response.     

Muscle fibre type distribution of the thoracolumbar and hindlimb regions of horses: relating fibre type and functional role

Background

Although the majority of equine muscles have a mixed fibre type distribution indicative of diverse functional roles, the predominance of a fibre type can indicate the primary function of a muscle. The deep epaxial musculature has an important role in core spinal stability in humans, reflected as a predominantly muscle fibre type (MFT) I or postural fibre type. The fibre type of the deep epaxial musculature has not been determined in horses. The objective of the study was to determine the MFT distribution in selected muscles of thoracolumbar and hindlimb region of horses. This included deep epaxial and hypaxial muscles that were hypothesised to have a postural stabilising role. A second objective was to examine differences in MFT distribution between horses bred for endurance (Arabian) and sprinting (Quarter horse). Muscle biopsy samples were obtained from selected thoracolumbar and hind limb muscles of 5 Quarter horses, 4 Arabians, and 2 Thoroughbreds. The myosin heavy chain distribution was determined by gel electrophoresis. Mann–Whitney rank test was used to compare the proportional MFT and differences between breeds.

Results

Mm. sacrocaudalis dorsalis medialis and diaphragm had the highest proportion of MFT-I. The remaining deep epaxial muscles and the hypaxial muscle m. psoas minor had approximately equal MFT I and II proportions. Mm. psoas major, iliocostalis, longissimus dorsi and the hind limb muscles contained mostly MFT-IIX. The fibre type distribution was similar between Arabians and Quarter horses, although Quarter horses had more MFT-IIX fibres in psoas major (P = 0.02) while Arabians had more MFT-I fibres in m. longissimus dorsi (P = 0.03).

Conclusions

The fibre type distribution of the deep epaxial muscles, mm psoas minor and diaphragm varied from approximately equal MFT-I and II proportions to predominantly MFT-I suggesting a postural stabilising role possibly important in core spinal stability. In contrast the fibre type proportions of mm psoas major, iliocostalis, longissimus dorsi and the hind limb muscles were mainly MFT-II suggesting a locomotory role. Knowledge of fibre type distribution in such a clinically important area can direct diagnosis, prevention and treatment of muscular or neuromotor dysfunction.     

Muscle fibre characteristics of active and inactive standardbred horses

Muscle biopsies were taken from the middle gluteus muscle of 36 Standardbred horses. Twelve of the horses were inactive, while 24 were actively trained and raced. Twelve of the trained horses were moderate performers, with a mean racing time of 1 min 21 secs per km (741 m/min) and the other 12 were excellent performers, with a mean racing time of 1 min 16 secs per km (789 m/min). The percentage and mean area of Type I fibres were similar in all three groups of horses. Marked differences were found among the subgroups of Type II fibres. The well-trained horses had a higher proportion of Type IIA fibres and a lower proportion of the Type IIB (58 per cent IIA and 15 per cent IIB fibres in the excellent performers; 49 per cent IIA and 26 per cent IIB in the moderate performers) than the inactive horses (41 per cent IIA and 35 per cent IIB fibres). The mean area of Type II fibres was smaller in the muscle of the active horses (excellent performers: IIA, 3075 micron2; IIB, 3378 micron2) moderate performers: IIA, 3185 micron2; IIB, 4252 micron2) than in that of the inactive ones (IIA, 3714 micron2; IIB, 5935 micron2). Intramuscular substrates (glycogen and triglycerides) and the activities of enzymes used as markers for the glycolytic potential of the muscle seemed to be similar in the three groups of horses, although there were large interindividual variation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Retrospective analysis of exploratory laparotomies in 192 Andalusian horses and 276 horses of other breeds

The medical records of 468 horses that underwent 490 exploratory laparotomies for the correction of gastrointestinal diseases were reviewed to search for differences between Andalusian horses and other breeds. The seasonal distribution of surgical colics and their outcome and complications were also investigated. Bivariant analysis was used to compare the horses' age, gender and breed with the type of surgery, the bowel affected and the type of colic, and all these variables were compared in relation to euthanasia during surgery, complications, short-term survival and seasonal distribution. A total of 405 horses survived the surgery and 329 were discharged from the hospital. Horses less than one year old had better short-term survival than older horses. Andalusian horses suffered more inguinal hernias than the other breeds and were more prone to suffer laminitis as a complication. Colic surgery and inguinal hernias were also more common in the summer.     

Locomotor, cardiocirculatory and metabolic adaptations to training in Andalusian and Anglo-Arabian horses

The effects of two training programmes in 20 Andalusian and 12 Anglo-Arabian horses were evaluated by an increasing intensity work test at velocities of 4, 5, 6, 7 and 8 m sec(-1). Heart rate was monitored and blood samples were drawn at rest and after each velocity to analyse packed cell volume, haemoglobin concentration, plasma lactate and potassium levels. Furthermore, the programmes were video-taped and stride length, duration and frequency, stance (restraint and propulsion), swing phase durations and stride vertical component were measured. The training protocol of the Andalusian horses produced significant decreases in the cardiovascular, haematological and metabolic responses to exercise. Locomotory training adaptation consisted of an increased stride frequency and a reduced stride length and vertical stride component. The last variable was the limiting factor of stride length both before and after training in the Andalusian horses. A different training protocol for show-jumping competition in Anglo-Arabian horses failed to show significant differences in the studied parameters to the work test, although an increase in stride length at velocities of over 6 m sec(-1) was observed. Stride vertical component did not have an effect on the physiological response to exercise, either before or after training.     

Comparative biokinematic study of young and adult Andalusian horses at the trot

The purpose of this study was to determine basic kinematic parameters (linear, temporal and angular) in young and adult Andalusian horses (P.R.E.) at the trot, using a normal computer-aided videography system. The trotting gaits of 16 horses were analysed: seven young horses (3.7 +/- 0.2 years old, height at withers 167.1 +/- 4.1 cm) and nine adult stallions (12.3 +/- 2.9 years old, height at withers 162.9 +/- 3.6 cm) were recorded at least 6 times at the trot using a 25-Hz video-camera filming from the side. Video images were processed with a real-time digital system (SMVD). Speeds averaged 3.84 and 3.75 m/s for young and adult horses, respectively. Differences between age groups for speed and linear and temporal parameters of the stride were not significant. However, variations in angular parameters were detected: adults showed a greater ARM than younger horses for most forelimb joints. In the hind limb, hip, stifle, and, to a lesser degree, the tarsal joint, a smaller degree of extension during the stance phase was observed in adult horses.     

Kinematic characteristics of Andalusian, Arabian and Anglo-Arabian horses: a comparative study

The aim of this study was to compare the kinematic trot characteristics of three different breeds of horse: Andalusian (AN, n = 15), Arabian (AR, n = 7) and Anglo-Arabian (AA, n = 5) using standard computer-assisted videography (25 Hz). Linear, temporal and angular parameters in fore- and hind limbs were analysed in six randomly selected strides per horse. Normalised angle-time diagrams along the complete stride were obtained for all joints angles in each breed and specific kinematic characteristics were detected graphically. AA horses displayed longer swing durations in both limbs ans a shorter angular range of motion (ARM) in scapula and pelvis inclination and in shoulder, hip and forelimb retraction-protraction angles. At lift off, stifle and tarsal joint angles were more flexed. In general, only small differences were observed in AR horse kinematics when compared with the other 2 breeds. AN horses presented negative overtracking length, which was positive in AR and AA. In AN horses the elbow and carpal joints were more flexed at the moment of maximal elevation, elbow and fore-fetlock joints also exhibited a larger ARM due to a smaller angle at maximal flexion. In the hind limbs, tarsal, hind fetlock and retraction-protraction angles presented a larger ARM in AN horses due to greater maximal flexion in the tarsal and hind fetlock joints. Fore- and hind fetlocks were also more flexed in horses from this breed. In conclusion, differences between kinematic variables at the trot were observed in the three breeds studied here, mainly in forelimb joints. The most outstanding feature was the greater forelimb flexion recorded in AN horses than in the other breeds which is consistent with the elevated movements in this breed. In AA horses, the ARM of proximal joints involved in retraction protraction in both fore- and hind limbs was smaller. All the differences observed highlighted the idiosyncratic nature of the trot in each breed; this may influence the functional capacity of each breed.     

Reference values for echocardiographic parameters of trained and untrained Icelandic horses

The aim of this study was to establish echocardiographic reference values for healthy Icelandic horses. For this purpose cardiologic examinations were performed on 44 healthy trained and untrained Icelandic horses without known cardiologic or pulmonary disease. The atrial diameter of the trained horses were significantly greater than in the untrained horses and the left ventricular free wall diameter was also higher in the trained than in the untrained horses. These findings confirm that the changes of the heart caused by training which have previously been described by other authors in warmbloods, thoroughbreds, dogs and humans are present in Icelandic horses as well. However, in contrast to the findings in race horses, no enlargement of the left ventricle was found in trained Icelandic horses, which may indicate that training conditions of Icelandic horses are not comparable to those of race- or jumping-horses in high level training. The reference values established in this study will serve as basis for the current interpretation of the results of echocardiographic examinations in Icelandic horses. This should enable cardiologists to perform a more detailed and precise examination similar to cardiological examinations in warmbloods and race horses.     

Assessment of inbreeding depression for body measurements in Spanish Purebred (Andalusian) horses

Our aim was to ascertain inbreeding depression in the Spanish Purebred horses for eight body measurements. A total of 16,472 individuals were measured for height at withers, height at chest, leg length, body length, width of chest, heart girth circumference, knee perimeter and cannon bone circumference. Three different multivariate animal models including, respectively, no measure of inbreeding, individual inbreeding coefficients (F_i) or individual increase in inbreeding coefficients (ΔF_i) as linear covariates were used. Significant inbreeding depression was assessed. Even though the models including measures of inbreeding fitted better with data, no effect on estimates of genetic parameters was assessed. However, the inclusion of inbreeding measures affected the ranking order according to the Expected Breeding Values (EBV). Due to the better fit with data and nice properties (the adjustment of individual inbreeding coefficients with the pedigree depth and linear behaviour) the use of ΔF_i in the evaluation models can be recommended for morphological traits in horses.     

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

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

Tendon injuries in horses treated with carbon fibre implants

Implants of carbon fibre, made by plaiting a tow of 10,000 filaments of Grafil type HT-S, were used to treat strains and ruptures of digital flexor tendons in 46 horses. The relevant clinical data, the techniques employed and an analysis of the results are described. Apart from two horses in which the implant was extruded and had to be removed, there were minimal untoward consequences of the surgery. Of the 34 horses with acute or chronic tendinitis, 14 returned to racing, seven were used as hunters and seven as hacks. Among the former group, seven suffered a further strain while racing but the others performed well for some time. Twelve horses with severed tendons recovered well and only in one did infection occur. Overall the results in the latter were better than had previously been achieved using other repair materials.     

Effect of atropine-dobutamine stress test on left ventricular echocardiographic parameters in untrained warmblood horses

The aim of this study was to investigate the effect of combined atropine low-dose dobutamine stress test on left ventricular parameters in adult warmblood horses, to establish a potential protocol for pharmacological stress echocardiography. Seven healthy untrained warmblood horses aged 9 to 22 years were used. Heart rate (HR) and left ventricular B- and M-mode dimensions were recorded at baseline and during stress testing with 35 microg/kg atropine IV followed by incremental dobutamine infusion of 2 to 6 microg/kg/min. HR increased significantly (P < .05) during the pharmacological challenge, and a maximal HR of 156.6 +/- 12.5 bpm was reached at maximal dobutamine infusion rate. Systolic and diastolic interventricular septum thickness, systolic and diastolic left ventricular free wall thickness, and fractional shortening increased significantly and reached a maximum at the highest infusion rate (mean +/- SD: 4.51 +/- 0.27 versus 5.65 +/- 0.31 cm, 2.89 +/- 0.19 versus 3.78 +/- 0.10 cm, 3.72 +/- 0.34 versus 4.77 +/- 0.18 cm, 2.44 +/- 0.28 versus 3.11 +/- 0.34 cm, 34.98 +/- 3.82 versus 50.56 +/- 3.42%, respectively). Systolic and diastolic left ventricular internal diameter decreased significantly during dobutamine infusion. Left ventricular external and internal area were significantly lower at a dobutamine infusion rate of 2 microg/kg/min but no further decrease was observed during the subsequent steps. Systolic and diastolic myocardial area was significantly lower after the administration of dobutamine but not significantly different during dobutamine infusion, when compared to baseline values. This pharmacological stress test induced significant changes in left ventricular echocardiographic parameters in adult warmblood horses. Additional research should evaluate the value of this stress test in horses suffering from cardiac disease.     

Treatment of sprained tendons in horses with carbon fibre implants

A technique for implanting carbon fibre into sprained flexor tendons in horses is described. Insertion of the fibres through paravertebral needles which passed through the affected region of the tendon was considered to be preferable to direct implantation into the surgically opened tendon. The results of the eight cases treated to date are dealt with briefly, together with a discussion as to how this form of treatment could be further evaluated.