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Abstract

Objective—To determine the effect of differences in structural and mechanical tendon properties on functionality of the passive stay apparatus in horses.

Sample—5 forelimbs each from nondwarf Friesians, dwarf Friesians, and ponies.

Procedures—Harvested forelimbs were loaded to test the passive stay apparatus. Tendons that stabilize the distal portion of the limb (superficial digital flexor tendon, deep digital flexor tendon, and tendo interosseus [suspensory ligament]) were isolated, and force-elongation data were obtained. Bone lengths, initial tendon lengths, and initial tendon cross-sectional areas were measured, and Young moduli were calculated. A model was used to determine whether joint angles could be explained by these 4 factors only.

Results—Dwarf limbs were unable to stand passively under loading because tendons that prevent overextension of the distal limb joints were too long and compliant to prevent over-extension. Tendon properties of limbs of nondwarf Friesians appeared to be intermediate between those of ponies and dwarf Friesians.

Conclusions and Clinical Relevance—Dysfunction of the passive stay apparatus in dwarf Friesians could be related to differences in structural and material properties of the tendons that result in hyperextension of the joints under loading. Nondwarf Friesians had intermediate tendon properties, which might be a breed-specific variation. Results indicated that certain tendon properties were associated with load failure of the stay apparatus and provided additional information about the functionality and requirements of the passive stay apparatus.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the mechanism that enables horses to partially counteract the shift of the center of pressure under the hoof induced by changes in hoof morphology attributable to growth and wear during a shoeing interval.

Animals—18 clinically sound Warmblood horses.

Procedures—Horses were evaluated 2 days and 8 weeks after shoeing during trotting on a track containing pressure-force measuring plates and by use of a synchronous infrared gait analysis system set at a frequency of 240 Hz. All feet were trimmed toward straight alignment of the proximal, middle, and distal phalanges and shod with standard flat shoes.

Results—Temporal characteristics such as stance time and the time between heel lift and toe off (ie, breakover duration) did not change significantly as a result of shoeing interval. Protraction and retraction angles of the limbs did not change. Compensation was achieved through an increase in the dorsal angle of the metacarpohalangeal or metarsophalangeal (fetlock) joint and a concomitant decrease of the dorsal angle of the hoof wall and fetlock. There was an additional compensatory mechanism in the hind limbs during the landing phase.

Conclusions and Clinical Relevance—Horses compensate for changes in hoof morphology that develop during an 8-week shoeing interval such that they are able to maintain their neuromuscular pattern of movement. The compensation consists of slight alterations in the angles between the distal segments of the limb. Insight into natural compensation mechanisms for hoof imbalance will aid in the understanding and treatment of pathologic conditions in horses.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To investigate the effects of early training for jumping by comparing the jumping technique of horses that had received early training with that of horses raised conventionally.

Animals—40 Dutch Warmblood horses.

Procedure—The horses were analyzed kinematically during free jumping at 6 months of age. Subsequently, they were allocated into a control group that was raised conventionally and an experimental group that received 30 months of early training starting at 6 months of age. At 4 years of age, after a period of rest in pasture and a short period of training with a rider, both groups were analyzed kinematically during free jumping. Subsequently, both groups started a 1-year intensive training for jumping, and at 5 years of age, they were again analyzed kinematically during free jumping. In addition, the horses competed in a puissance competition to test maximal performance.

Results—Whereas there were no differences in jumping technique between experimental and control horses at 6 months of age, at 4 years, the experimental horses jumped in a more effective manner than the control horses; they raised their center of gravity less yet cleared more fences successfully than the control horses. However, at 5 years of age, these differences were not detected. Furthermore, the experimental horses did not perform better than the control horses in the puissance competition.

Conclusions and Clinical Relevance—Specific training for jumping of horses at an early age is unnecessary because the effects on jumping technique and jumping capacity are not permanent. (Am J Vet Res 2005;66:418–424)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To quantify variation in the jumping technique within and among young horses with little jumping experience, establish relationships between kinetic and kinematic variables, and identify a limited set of variables characteristic for detecting differences in jumping performance among horses.

Animals—Fifteen 4-year-old Dutch Warmblood horses.

Procedure—The horses were raised under standardized conditions and trained in accordance with a fixed protocol for a short period. Subsequently, horses were analyzed kinematically during free jumping over a fence with a height of 1.05 m.

Results—Within-horse variation in all variables that quantified jumping technique was smaller than variation among horses. However, some horses had less variation than others. Height of the center of gravity (CG) at the apex of the jump ranged from 1.80 to 2.01 m among horses; this variation could be explained by the variation in vertical velocity of the CG at takeoff ( r, 0.78). Horses that had higher vertical velocity at takeoff left the ground and landed again farther from the fence, had shorter push-off phases for the forelimbs and hind limbs, and generated greater vertical acceleration of the CG primarily during the hind limb pushoff. However, all horses cleared the fence successfully, independent of jumping technique.

Conclusions and Clinical Relevance—Each horse had its own jumping technique. Differences among techniques were characterized by variations in the vertical velocity of the CG at takeoff. It must be determined whether jumping performance later in life can be predicted from observing free jumps of young horses. ( Am J Vet Res 2004;65:938–944)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether differences in jumping technique among horses are consistent at various ages.

Animals—12 Dutch Warmblood horses.

Procedure—Kinematics were recorded during free jumps of horses when they were 6 months old (ie, no jumping experience) and 4 years old (ie, the horses had started their training period to become show jumpers). Mean ± SD height of the horses was 1.40 ± 0.04 m at 6 months of age and 1.70 ± 0.05 m at 4 years of age.

Results—Strong correlations were found between values from 6-month-old foals and 4-year-old horses for variables such as peak vertical acceleration generated by the hind limbs ( r, 0.91), peak rate of change of effective energy generated by the hind limbs ( r, 0.71), vertical velocity at takeoff ( r, 0.65), vertical displacement of the center of gravity during the airborne phase ( r, 0.81), and duration of the airborne phase ( r, 0.70).

Conclusions and Clinical Relevance—Although there are substantial anatomic and behavioral changes during the growing period, certain characteristics of jumping technique observed in naïve 4-year-olds are already detectable when those horses are foals. ( Am J Vet Res 2004;65:945–950)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate the effect of various head and neck positions on intrathoracic pressure and arterial oxygenation during exercise in horses.

Animals—7 healthy Dutch Warmblood riding horses.

Procedures—The horses were evaluated with the head and neck in the following predefined positions: position 1, free and unrestrained; position 2, neck raised with the bridge of the nose aligned vertically; position 4, neck lowered and extremely flexed with the nose pointing toward the pectoral muscles; position 5, neck raised and extended with the bridge of the nose in front of a vertical line perpendicular to the ground surface; and position 7, neck lowered and flexed with the nose pointing towards the carpus. The standard exercise protocol consisted of trotting for 10 minutes, cantering for 4 minutes, trotting again for 5 minutes, and walking for 5 minutes. An esophageal balloon catheter was used to indirectly measure intrathoracic pressure. Arterial blood samples were obtained for measurement of Pao2, Paco2, and arterial oxygen saturation.

Results—Compared with when horses were in the unrestrained position, inspiratory intrathoracic pressure became more negative during the first trot (all positions), canter and second trot (position 4), and walk (positions 4 and 5). Compared with when horses were in position 1, intrathoracic pressure difference increased in positions 4, 2, 7, and 5; Pao2 increased in position 5; and arterial oxygen saturation increased in positions 4 and 7.

Conclusions and Clinical Relevance—Position 4 was particularly influential on intrathoracic pressure during exercise in horses. The effects detected may have been caused by a dynamic upper airway obstruction and may be more profound in horses with upper airway disease.

Full access
in American Journal of Veterinary Research