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Gomez Alvarez, C. B., Rhodin, M., Bobber, M. F., Meyer, H., Weishaupt, M. A., Johnston, C., et al. (2006). The effect of head and neck position on the thoracolumbar kinematics in the unridden horse. Equine Vet J Suppl, (36), 445–451.
Abstract: REASONS FOR PERFORMING STUDY: In many equestrian activities a specific position of head and/or neck is required that is dissimilar to the natural position. There is controversy about the effects of these positions on locomotion pattern, but few quantitative data are available. OBJECTIVES: To quantify the effects of 5 different head and neck positions on thoracolumbar kinematics of the horse. METHODS: Kinematics of 7 high level dressage horses were measured walking and trotting on an instrumented treadmill with the head and neck in the following positions: HNP2 = neck raised, bridge of the nose in front of the vertical; HNP3 = as HNP2 with bridge of the nose behind the vertical; HNP4 = head and neck lowered, nose behind the vertical; HNP5 = head and neck in extreme high position; HNP6 = head and neck forward and downward. HNP1 was a speed-matched control (head and neck unrestrained). RESULTS: The head and neck positions affected only the flexion-extension motion. The positions in which the neck was extended (HNP2, 3, 5) increased extension in the anterior thoracic region, but increased flexion in the posterior thoracic and lumbar region. For HNP4 the pattern was the opposite. Positions 2, 3 and 5 reduced the flexion-extension range of motion (ROM) while HNP4 increased it. HNP5 was the only position that negatively affected intravertebral pattern symmetry and reduced hindlimb protraction. The stride length was significantly reduced at walk in positions 2, 3, 4 and 5. CONCLUSIONS: There is a significant influence of head/neck position on back kinematics. Elevated head and neck induce extension in the thoracic region and flexion in the lumbar region; besides reducing the sagittal range of motion. Lowered head and neck produces the opposite. A very high position of the head and neck seems to disturb normal kinematics. POTENTIAL RELEVANCE: This study provides quantitative data on the effect of head/neck positions on thoracolumbar motion and may help in discussions on the ethical acceptability of some training methods.
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Weishaupt, M. A., Wiestner, T., von Peinen, K., Waldern, N., Roepstorff, L., van Weeren, R., et al. (2006). Effect of head and neck position on vertical ground reaction forces and interlimb coordination in the dressage horse ridden at walk and trot on a treadmill. Equine Vet J Suppl, (36), 387–392.
Abstract: REASONS FOR PERFORMING STUDY: Little is known in quantitative terms about the influence of different head-neck positions (HNPs) on the loading pattern of the locomotor apparatus. Therefore it is difficult to predict whether a specific riding technique is beneficial for the horse or if it may increase the risk for injury. OBJECTIVE: To improve the understanding of forelimb-hindlimb balance and its underlying temporal changes in relation to different head and neck positions. METHODS: Vertical ground reaction force and time parameters of each limb were measured in 7 high level dressage horses while being ridden at walk and trot on an instrumented treadmill in 6 predetermined HNPs: HNP1 – free, unrestrained with loose reins; HNP2 – neck raised, bridge of the nose in front of the vertical; HNP3 – neck raised, bridge of the nose behind the vertical; HNP4 – neck lowered and flexed, bridge of the nose considerably behind the vertical; HNP5 – neck extremely elevated and bridge of the nose considerably in front of the vertical; HNP6 – neck and head extended forward and downward. Positions were judged by a qualified dressage judge. HNPs were assessed by comparing the data to a velocity-matched reference HNP (HNP2). Differences were tested using paired t test or Wilcoxon signed rank test (P<0.05). RESULTS: At the walk, stride duration and overreach distance increased in HNP1, but decreased in HNP3 and HNP5. Stride impulse was shifted to the forehand in HNP1 and HNP6, but shifted to the hindquarters in HNP5. At the trot, stride duration increased in HNP4 and HNP5. Overreach distance was shorter in HNP4. Stride impulse shifted to the hindquarters in HNP5. In HNP1 peak forces decreased in the forelimbs; in HNP5 peak forces increased in fore- and hindlimbs. CONCLUSIONS: HNP5 had the biggest impact on limb timing and load distribution and behaved inversely to HNP1 and HNP6. Shortening of forelimb stance duration in HNP5 increased peak forces although the percentage of stride impulse carried by the forelimbs decreased. POTENTIAL RELEVANCE: An extremely high HNP affects functionality much more than an extremely low neck.
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Ratzlaff, M. H., Wilson, P. D., Hyde, M. L., Balch, O. K., & Grant, B. D. (1993). Relationship between locomotor forces, hoof position and joint motion during the support phase of the stride of galloping horses. Acta Anat (Basel), 146(2-3), 200–204.
Abstract: Three methods were used simultaneously to determine the relationships between the vertical forces exerted on the hooves and the positions of the limbs and hooves at the times of peak vertical forces from 2 horses galloping on a track straightaway. Vertical forces were recorded from an instrumented shoe, fetlock joint motion was measured with an electrogoniometer and the angles of the carpus, fetlock and hoof were determined from slow-motion films. At hoof contact, the mean angles of the carpus and fetlock were 181-182 degrees and 199-206 degrees, respectively. Peak vertical forces on the heel occurred at or near maximum extension of the carpal and fetlock joints. Peak forces on the toe occurred during flexion of the fetlock joint and at mean hoof angles of 28-31 degrees from the horizontal. The mean angles of the hoof from the horizontal at the time of heel contact were 6-7 degrees. Hoof lift occurred at mean carpal angles of 173-174 degrees and mean fetlock angles of 199-200 degrees.
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Colahan, P., Lindsey, E., & Nunier, C. (1993). Determination of the center of pressure of the hoofs of the forelimbs of horses standing on a flat level surface. Acta Anat (Basel), 146(2-3), 175–178.
Abstract: The pressure exerted on a flat level surface by recently trimmed, unshod hoofs of the front limbs of 23 sound, adult horses was measured using pressure-sensitive film and a specially built cassette. The horses were tranquilized and stood with one foot on the 2.9-cm-thick cassette and the other on a block of equal height. The hoofs were observed for motion during the measurement, and the developed film was examined for improper alignment of the film or slipping of the hoof. The center of pressure was located using the method of weighted proportions of Barrey. This static measurement system with a long measurement time and the number of measurements reduced the influence of variables inherent in the horses' behavior and the measuring system. The calculated point was recorded as falling medial to, lateral to or on a line bisecting the central sulcus of the frog. In the dorsal to palmar orientation the point was classified with reference to a line drawn halfway between the most dorsal and the most palmar mark on the film. Forty-six percent of the calculated centers of pressure were located in the medial heel area. Binomial analysis for large samples indicates that this was a significant variation from a random distribution. Seventy-six percent of the centers were located in or on the borders of the medial heel.
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Clayton, H. M. (1993). The extended canter: a comparison of some kinematic variables in horses trained for dressage and for racing. Acta Anat (Basel), 146(2-3), 183–187.
Abstract: This study was designed to test the hypothesis that there is no significant difference in selected temporal and linear stride variables of the extended canter in horses bred and trained for dressage or racing. Nine advanced-level dressage horses and 7 Thoroughbred racehorses were filmed at a frame rate of 200 Hz at an extended canter on a sand track. Two strides were recorded per trial, and each horse performed 6 or 7 trials. Temporal and linear data were determined from the films, and descriptive statistics (mean, SD) were calculated. Strides were selected for analysis on the basis of having a velocity in the range of 6.0-7.0 m/s, and multivariate analysis of variance was used to detect significant differences in the stride kinematics of horses trained for the two sports (p < or = 0.01). The average velocity of the dressage horses was 6.37 m/s, compared with 6.40 m/s for the racehorses. There were no significant differences between the two groups in velocity, stride duration, stride length or the distances between limb placements. The stance durations of all four limbs and the overlaps between them were longer, whereas the duration of the suspension phase was shorter in the dressage horses than in the racehorses (p < or = 0.01). The time between impacts of the diagonal limb pair was close to zero in both groups, with individual horses showing some variability in the order of placement of the diagonal limb pair. However, the sequence of footfalls was not significantly different between the two groups (p < or = 0.01).
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Argue, C. K., & Clayton, H. M. (1993). A preliminary study of transitions between the walk and trot in dressage horses. Acta Anat (Basel), 146(2-3), 179–182.
Abstract: The object of this study was to determine the limb support sequence during the transitions from walk to trot and from trot to walk in dressage horses under saddle and to test the null hypothesis that the limb support sequence during the transitions is not related to the level of training. Sixteen dressage horses training at novice to FEI Grand Prix level were videotaped performing an average of 9 transitions each from walk to trot and from trot to walk. The 30-Hz videotapes were viewed in slow motion, and based on the limb support sequence the transitions were categorized into two types. In type 1 transitions there were no intermediate steps between the walk and trot sequences. Type 2 transitions were characterized by intermediate steps, including a single support phase. The Kendall rank-order correlation coefficient showed that a higher level of training was positively associated with an increased percentage of type 1 transitions for both walk-to-trot transitions (p < or = 0.05) and trot-to-walk transitions (p < or = 0.01). No significant preference for initiating or completing the trot on the left or right diagonal was found using the binomial test for individual horses and the Wilcoxon signed-ranks test for the group.
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Williams, D. O., Boatwright, R. B., Rugh, K. S., Garner, H. E., & Griggs, D. M. J. (1991). Myocardial blood flow, metabolism, and function with repeated brief coronary occlusions in conscious ponies. Am J Physiol, 260(1 Pt 2), H100–9.
Abstract: Studies were performed in the conscious pony instrumented with a Doppler flow probe and hydraulic occluder on the left anterior descending coronary artery (LAD), sonomicrometry crystals and intraventricular micromanometer in the left ventricle, and catheters in the left atrium and anterior interventricular vein. Two-minute LAD occlusions were performed every 30 min continuously or during working hours. Data on release of catabolites (potassium, hydrogen ions, and lactate) and norepinephrine from the initially dysfunctional region were obtained periodically during a regimen of 445 +/- 56 occlusions in six animals. Regional myocardial blood flow was measured (microsphere method) before and after an occlusion regimen in four animals. Marked release of catabolites and norepinephrine from the initially dysfunctional region was noted in association with early occlusions when myocardial segment function was severely reduced. With further occlusions, release of these substances decreased while segment function improved. Blood flow was markedly decreased in the initially dysfunctional region during an early occlusion but was at the control level during a later occlusion. Although the metabolic findings are consistent with protection due to “ischemic preconditioning” and no increase in collateral perfusion, the inverse relationship noted between catabolite release and segment function is best explained by flow-dependent mechanisms. These results, together with the myocardial blood flow data, serve to validate a previous assumption that protection against regional myocardial dysfunction under these conditions is due to increased collateral perfusion.
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Spadavecchia, C., Arendt-Nielsen, L., Andersen, O. K., Spadavecchia, L., Doherr, M., & Schatzmann, U. (2003). Comparison of nociceptive withdrawal reflexes and recruitment curves between the forelimbs and hind limbs in conscious horses. Am J Vet Res, 64(6), 700–707.
Abstract: OBJECTIVE: To compare nociceptive withdrawal reflexes (NWRs) evoked from the distal aspect of the left forelimb and hind limb in conscious standing horses and to investigate NWR recruitment for graded electrical stimulation intensities. ANIMALS: 20 adult horses. PROCEDURE: Surface electromyographic (EMG) activity evoked by transcutaneous electrical stimulation of the digital palmar (or plantar) nerve was recorded from the common digital extensor and cranial tibial muscles. Stimuli consisted of 25-millisecond train-of-5 constant current pulses. Current intensity was gradually increased until NWR threshold intensity was reached. The EMG signal was analyzed for quantification of the NWR. Behavioral responses accompanying the reflex were scored (scale, 0 to 5). The NWR recruitment curves were determined at 0.9, 1.1, 1.2, and 1.3 times the NWR threshold intensity. RESULTS: The NWR threshold was significantly higher for the hind limb (median value, 6.6 mA; range, 3 to 10 mA) than the forelimb (median, 3 mA; range, 1.7 to 5.5 mA). The NWR of the hind limb had a significantly longer latency (median, 122.8 milliseconds; range, 106 to 172 milliseconds), compared with the forelimb (median, 98 milliseconds; range, 86 to 137 milliseconds), and it was associated with significantly stronger behavioral reactions. Gradual increase of NWR amplitude was evident at increasing stimulation intensities and supported by the behavioral observations. CONCLUSIONS AND CLINICAL RELEVANCE: We documented NWRs evoked from the forelimb and hind limb and their recruitment with stimuli of increasing intensity in horses. These results provide a basis for use of NWRs in studies on nociceptive modulation in horses.
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Keiper, R., & Houpt, K. (1984). Reproduction in feral horses: an eight-year study. Am J Vet Res, 45(5), 991–995.
Abstract: The reproductive rate and foal survival of the free-ranging ponies on Assateague Island National Seashore were studied for 8 years, 1975 to 1982. Most (52%) of the 86 foals were born in May, 13% were born in April, 22.6% in June, 10.4% in July, and less than 1% in August and September. The mean foaling rate was 57.1 +/- 3.9% and the survival rate was 88.3 +/- 3.6%. Forty-eight colts and 55 fillies were born (sex ratio 53% female). Mares less than 3 years old did not foal and the foaling rate of 3-year-old mares was only 23%, that of 4-year-old mares was 46%, that of 5-year-old mares was 53%, and 6-year-old mares was 69%. The relatively poor reproduction rate was believed to be a consequence of the stress of lactating while carrying a foal when forage quality on the island was low. The hypothesis was supported by the higher reproductive rate (74.4 +/- 2.4%) of the ponies in the Chincoteague National Wildlife Refuge on the southern part of the island. Their foals are weaned and sold in July each year. Despite the low reproductive rate on Assateague Island National Seashore , the number of ponies increased from 43 to 80, a 90% increase in the 8-year period or greater than 10%/yr. There were 24 deaths and 8 dispersals from the study area.
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Kurvers, C. M. H. C., van Weeren, P. R., Rogers, C. W., & van Dierendonck, M. C. (2006). Quantification of spontaneous locomotion activity in foals kept in pastures under various management conditions. Am J Vet Res, 67(7), 1212–1217.
Abstract: OBJECTIVE: To describe spontaneous locomotion activity of foals kept under various management conditions and assess the suitability of global positioning system (GPS) technology for recording foal activity. Animals-59 foals. PROCEDURES: During the foals' first 4 months of life, 921 observation periods (15 minutes each) were collected and analyzed for locomotion activities. The GPS system was evaluated by simultaneously carrying out field observations with a handheld computer. RESULTS: Foals spent 0.5% of total observed time cantering, 0.2% trotting, 10.7% walking, 32.0% grazing, 34.8% standing, and 21.6% lying down. Total observed daytime workload (velocity x distance) in the first month was approximately twice that in the following months. Locomotion activity decreased with increasing age. Colts had more activity than fillies in certain periods, and foals that were stabled for some portion of the day had compensatory locomotion activity, which was probably insufficient to reach the level of foals kept continually outside. The GPS recordings and handheld-computer observations were strongly correlated for canter, trot, and walk and moderately correlated for standing and lying. Correlation for grazing was low. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that domestically managed foals, when kept 24 h/d at pasture, will exercise at a level comparable with feral foals. High workload during the first month of life might be important for conditioning the musculoskeletal system. The GPS technique accurately quantified canter, trot, and walk activities; less accurately indexed resting; and was unsuitable for grazing because of the wide array of velocities used while foraging.
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