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Horse Weigh is a company that provides a range of horse weighing platforms. It is also the exclusive UK and Ireland distributor for Kraft Horse Walkers.

Report

A Review of the Potential Benefits
of Oval Horsewalkers

Paul Farrington BvetMed MRCVS and Dr David Marlin BSc (Hons) PhD
Date of Report - 1st November 2006

INTRODUCTION
Horsewalkers (electro-mechanical devices that allow multiple horses to be exercised simultaneously in a controlled fashion) are used extensively in the management and training of horses. They permit controlled exercise of horses at walk and trot. They are less labour intensive than other forms of controlled exercise, such as walking in-hand, lunging or riding. Horsewalkers may be used for a variety of reasons including warming-up or cooling down prior to ridden exercise, as a way to relieve boredom in stabled horses, for controlled exercise as part of a rehabilitation programme and to supplement ridden exercise. Horsewalkers are often also used where ridden exercise is not desirable or possible, such as in preparation of young animals for sale. The majority of horses can be trained to accept being exercised on a walker within a short period of time. Any form of exercise carries a risk of injury and whilst there does not appear to be any objective information on the safety of this form of exercise, it would generally be considered that the Horsewalker is a very safe form of exercise.

Until recently, Horsewalkers have been exclusively of a round design in which the horse is constantly turning on a circular track. The radius (tightness) of the turn is determined by the diameter of the walker – the large the walker, the more gradual the turn. At present commercial round Horsewalkers vary from around 10 to 30 metres in diameter. The conventional design is of a centre post from which radiate arms that support the moving dividers that separate the horses but also encourage them to walk as the centre post rotates, in turn moving the dividers. Whilst the majority of walkers can operate in either a clockwise or anti-clockwise direction, whilst on the walker the horse is still turning constantly.

Exercising at walk or trot on a circle for prolonged periods of time must be considered to a large extent unnatural for a horse. Horses at pasture, whether grazing or exercising, move in all directions and never in one continuous direction. The same is true of ridden exercise. No rider would work his or her horse continuously for 30 minutes on a circle, even when working in a confined area. For example, a Dressage test incorporates many changes in rein and exercise in straight lines as well as on turns. Lunging is another mode of controlled, unridden, exercise that is commonly used by horse owners or trainers. Lunging may be used in place of ridden exercise or to train riders or as a warm-up for the horse prior to it being mounted and ridden. However, prolonged lunging is not advisable and in addition, as with circular walkers, changing the rein frequently is common practice.

Continual turning may be deleterious to the musculoskeletal system (muscles, bones, tendons, ligaments and joints). For example, it is widely recognised that signs of lameness are exacerbated in horses exercised on a circle (Swanson 1988, Wright 1993). This is commonly used by veterinary surgeons in lameness investigations. It is also suspected that sharp turns may contribute to injury of distal limb structures (i.e. those structures furthest from the body such as the foot)(Dyson 1991; Chateau et al. 2005). This implies that turning exercise changes the weight distribution through the limbs. The surface on which a horse is lunged may also determine whether lameness is apparent or not; a horse may not exhibit lameness when lunged on a soft surface but may do so when lunged on the same size circle on a firmer or uneven surface.

Most research into how horses move has been concentrated in horses walking and trotting in straight lines, or on treadmills, and there are only a limited number of studies relating to horses turning on a circle.

Only one kinematic (movement) study (Chateau et al. 2005) has evaluated the effects of turning a corner on the distal joint motions. Horses turning in a sharp (1.5m diameter) left circle demonstrated that stride length is shortened, but stance duration (the amount of time the foot is on the ground) is longer. This work also showed that the lower leg and foot rotate as the weight of the horse moves over the limb.

Research from Australia (Davies & Merritt 2004) showed that the outside edge of the cannon bone is not loaded significantly during exercise in a straight line on a flat surface. The same group of researchers also showed in a separate study that surface strains on the cannon bone vary between inside and outside forelimbs during turning. On the inner surface of the cannon bone, compression of the bone is greatest in the outside limb, and stretching of the bone is greatest on the inside limb. On the outer surface of the cannon bone, both compressive and tensile peaks are largest on the inside limb, which also showed the largest recorded strains in compression. On the dorsal (front) surface of the bone (where bucked shins occur in young horses), compressive strains were largest on the outside limb, and were greater on larger circles. They concluded that turning exercise is required to maintain normal bone, in that low-speed exercise in a straight line only loads the outer edge of the cannon bone.

In 2006 workers from the US (Clayton et al. 2006) studied the effect of trotting in a circle on the centre of mass of the horse. The centre of mass is a point within or on the body at which the mass of the body is considered to act. The centre of mass may vary according to gait, speed and direction of travel. The location of the centre of mass affects the distribution and size of the loads on the limbs. These researchers showed that in horses trotting on the lunge on a 6m diameter circle at a speed of ~2 metres/second, all horses leaned inwards at an angle of ~15°. The speeds attained by these horses at trot on a circle are lower than those typically seen for horses on a straight line. As the speed was slower, the implication is that stance proportion was increased (i.e. the weight bearing phase of the stride was longer on a circle than would be expected in a straight line). Furthermore, the researchers pointed out that "horses may behave differently when turning clockwise versus counter-clockwise due to asymmetries in strength, suppleness and neural programming…". Thus, whilst it is often assumed that an equal amount of exercise on each rein on a circular Horsewalker should be applied, this may not be the case for many horses and may actually be counter-productive.

The potential negative impact of circular exercise has also been highlighted with respect to the muscular system: "Especially in the initial stages of a return to work avoid lunging, horse walkers, or work in tight circles, as well as hill work" ["Are we still Tied-Up in the 21st Century?" Dr Pat Harris PhD VetMB MRCVS, Equine Studies Group WALTHAM Centre for Pet Nutrition and WINERGY (Presented to Equine Centre Horse Health Care Precinct at Equitana 2003)].

Exercising on a circle also requires more effort than exercising in a straight line (Harris, Marlin, Davidson, Rodgerson, Gregory and Harrison, unpublished data). For example, being lunged on a 10 metre diameter circle was around 25% more work than being ridden on a large oval track in an indoor school. In addition, being lunged on a 5m circle was around 12% more work than being lunged on a 14 metre diameter circle. Even accounting for the weight of the rider, lunging is harder work than ridden exercise, which is most likely due to the continual effort required by the horse to balance itself on a continual turn.

The Oval Walker

German based manufacturer of Horsewalkers Kraft recently launched the first oval horsewalker. The premise being that continual exercise on a small circle is unnatural for horses and could even lead to injury and that a walker incorporating both straight line and turning exercise would represent a more appropriate form of controlled exercise. As so little information exists on turning in horses, a study was commissioned by Kraft and UK and Ireland distributor Horse Weigh to examine turning stress in horses in more detail. The study was designed by Paul Farrington (Veterinary surgeon) and Dr David Marlin (Physiologist) and the work was undertaken at Bristol University by Dr Bob Colborne (Specialist in Biomechanics).

The Research on Turning

The purpose of this study was to record the forces acting on the lower limb as horses walked in a straight line, on a 14 metre diameter circle, and on a 10 metre diameter circle to provide insight into the horizontal forces transmitted up the limb during locomotion in a straight line and whilst turning (A detailed report on the research can be obtained by contacting Horse Weigh).

Three fit, sound Thoroughbred horses, ages 3, 5 and 12 years of age were used in the study. Horses were then walked across a force-plate (a metal plate placed on the ground that measures the force with which the horses’ foot is placed on the ground) both in a straight line and on a 10 and 14 metre diameter turn. For the turns the horse was always walking on a left-turn.

The results show that the coffin joint has the greatest degree of abduction (movement of the limb away from the body), adduction (movement of the limb towards the body) and axial rotation (twisting movement) and that these movements are greatest at the time of impact and break-over. The first point of contact with the ground has a significant influence on the line of stress through the foot and up the limb, as does the position of the body at the same moment. On a turn the horse abducts the inside forelimb away from the body towards the line of the circle with rotation of the foot in the direction of the turn. The stride length is dictated by the tightness of the turn, as is the stance time (when the foot is on the ground). As the horse then moves forward the horse’s body moves towards the inside limb increasing the loading on the limb. The results show that on average the forelimbs tend to behave asymmetrically on a circle so that the forces and movements differ to produce different torque effects (twisting forces). The hind limbs tend to behave more symmetrically unless the size of the circle is reduced from 14 to 10 metres in diameter.

Importance of Horsewalker Surfaces

The walking surface will likely have an effect on the stresses experienced by a limb. If the surface allows reasonably free twisting of the hoof when weight bearing, the stresses between the hoof and ground will be small. However, any ground surface that holds the hoof and impedes this horizontal rotation will probably impart higher loads to the joints of the lower limb. Large turning forces should be avoided when the limb is vertically loaded (i.e. when the weight of the horse’s body is over the limb and the limb is on the ground). It is also important that the walking surface is level to avoid tilting of the hoof during weight-bearing. A walking track that is worn in the middle and that causes rotation of the joints in the foot is likely to cause larger and uneven forces to the lower limb joints and associated tendons and ligaments.

Implications for Oval versus Round Horsewalkers

The research commissioned by Horse Weigh/Kraft and a review of other scientific studies shows that turning is not equivalent to exercise in a straight line. Turning exercise is harder than exercise in a straight line and loads the bones in a different way. Furthermore, on small turns the inner and outer limbs may not behave in the same way as on larger circles. This may have implications for horses with pre-existing musculoskeletal injuries. The advantage of the oval walker is that it combines straight line and turning exercise that mimics the exercise that a horse will do when being ridden or when free at pasture.

Dr Colborne’s results have shown that hind limb patterns were quite
different in their signs on the tighter radius turns, indicating a
different strategy for turning, and supporting the notion that both
straight line and turning exercise is recommended for overall loading
patterns that are healthy for maintaining bone that can withstand loading
forces in a variety of directions.

The results also make clear that small diameter round walkers (~10 metre diameter or less) are less desirable than round walkers of 14 metre diameter or greater. Small diameter round walkers increase the loading and asymmetry and increase the work compared with larger diameter walkers. Small diameter round walkers are not recommended.

In conclusion, there appear to be significant advantages to using a walker of oval design as opposed to a round design as exercise on the oval loads the limbs with a combination of straight and turning movements, as would be experienced during riding or in free movement.

REFERENCES

Chateau H, Degueurce C and Denoix J-M. (2004) Evaluation of three-dimensional kinematics of the distal portion of the forelimb in horses walking in a straight line. American Journal of Veterinary Research, 65(4): 447-455.

Chateau H, Degueurce C and Denoix J-M. (2005) Three-dimensional kinematics of the equine distal forelimb: Effects of a sharp turn at the walk. Equine Veterinary Journal, 37(1): 12-18.

Clayton HM et al. 3D kinematics of the interphalangeal joints in the forelimb of walking and trotting horses. Veterinary and Comparative Orthopaedics and Traumatology (In press).

Clayton, HM and Sha, DH (2006) Head and body centre of mass movement in horses trotting on a circular path. Equine Exercise Physiology (7), Equine Vet J suppl 36, 462-467.

Davies HM and Merritt JS. (2004) Surface strains around the midshaft of the third metacarpal bone during turning. Equine Veterinary Journal, 36(8): 689-692.

Dyson SJ. (1991) Lameness due to pain associated with the distal interphalangeal joint: 45 cases. Equine Veterinary Journal, 23: 128-135.

Swanson TD. (1988) Degenerative disease of the proximal interphalangeal (pastern) joint in performance horses. Proceedings of the American Association of Equine Practitioners, 34: 393-397.

Wright IM. (1993) A study of 118 cases of navicular disease: Clinical features. Equine Veterinary Journal, 25(6): 477-481.

Paul Farrington BvetMed MRCVS

Dr David Marlin BSc (Hons) PhD

 

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