Many of you will be starting to get your horses fit with long-slow work. A good basis for increasing bone strength, muscular and cardiovascular fitness. Many of you will be using roads. Given the high prevalence of lameness and arthritic type injury/disease in horses here are some points to consider with respect to roadwork…
Roadwork results in forces on the hoof around 20x higher than working on good grass or artificial surfaces. A great deal of this is absorbed by the hoof, fetlock and bones below the knee but may still lead to damage to joints. Firm wet sand is better than roads but still around 8x harder than good grass or good arena surface.
Roadwork DOES NOT “harden” or strengthen tendons
Roadwork DOES increase bone strength – but you only need a few minutes of trot to achieve this
Roadwork DOES contribute to joint/cartilage deterioration
Roadwork – No limit to walking! Trotting should be LIMITED to no more than 5 minutes per day, in my opinion
Working on very SOFT SURFACES increases the risk of soft tissue (muscle, tendon, ligament) injuries
Working on UNEVEN surfaces carries an increased risk of injury.
In horses trotting in harness, the vertical impact (deceleration) was around 260 metres/second/second) for firm wet sand, 105 m/s/s for deep wet sand, 34 m/s/s for deep dry sand and 735 m/s/s for asphalt (the same as in the study by Barrey et al. 1991). (if you read the paper the values are correct in the figures but have been multiplied wrongly by a factor of 10 in the tables). Firm wet sand is better than roads but still around 8x harder than good grass or arena.
EXERCISE IN IMMATURE HORSES
There is evidence that increased controlled exercise can enhance tendon strength in young, musculo-skeletaly immature horses (horses less than approximately 2 years of age).
ROADWORK IN THE REHABILITATION OF TENDON INJURIES
A few people have raised the issue of roadwork in the rehabilitation following tendon injury so it may help to clarify this area. Exercise (of any kind) does not strengthen HEALTHY tendons in MATURE horses (horses >3 years of age). Exercise (of any kind) does result in PARTIAL repair of INJURED tendons. There is nothing special about roads – other than they (normally) provide a consistent, level and straight surface for controlled exercise which is essential for tendon rehabilitation. However, in rehabilitating your horses’ tendons with excessive amounts of roadwork you may well be damaging your horses’ joints significantly – which would be a consideration for horses with pre-existing joint disease. Also, although appropriate rehabilitation exercise promotes tendon repair (and in fact is essential for the tendon “fibres” to align properly), the evidence shows that the repaired tendon is:
a) not healthy normal tendon and contains scar tissue and tendon tissue with an abnormal structure;
b) is stiffer than before injury;
c) functions less well;
d) is more likely to be re-injured.
There is very little in the way of controlled scientific studies on hoofboots. The one study I am aware of compared the forces at walk in horses either unshod or wearing a Soft Ride hoof boot (made in the USA). The peak forces were similar with the boot and when unshod but with the hoof boot there was a small but significant increase in stance phase of 7% (the time when the hoof is on the ground) and the deceleration of the hoof was longer. Both of these would be considered beneficial. However, it does not follow that the same benefits would occur at trot and or canter. In addition, boots that cause the foot to grip more strongly could prevent sliding along the ground and lead to higher deceleration and increased strains within the foot and fetlock. More work needed.
Barefoot horses are at a similar risk from roadwork as shod horse with respect to forces transmitted up the leg (the difference between shod and unshod is in how the force travels through the foot). With our current knowledge, there is no reason to conclude that barefoot horses are at a lower risk of concussive damage from roadwork.
The presence of shoes does not change the overall/total force on the limb (which is determined by the mass of the horse and the rider) which has to be dissipated by the elastic structures of the limb (tendon, ligament, joint). However, metal shoes do cause greater vibration/concussion and detrimentally alter the kinematics of the stride. They also alter how the foot interacts with the ground and how the force is distributed throughout the foot (but not higher). Trotting on a road generates concussion and high peak forces in shod horses. These are lower in barefoot horses. However, a barefoot horse trotting on a road will still experience very high forces compared with say trotting on grass, although these will be less than for a shod horse. Bottom line. Just because a horse is barefoot doesn’t mean its OK to do hours of roadwork at trot.
From Lars Roepstorff’s study (Roepstorff et al. 1999) there was no difference in vertical force or vertical landing velocity (speed) of the hoof between shod and unshod horses at trot when ridden over a forceplate in an asphalt track (i.e. a “road”). Interestingly, the horizontal landing velocity was significantly lower for unshod horses, which suggests that the unshod foot “grips” a road-like surface more than a metal shoe. Jeff Tomason (1998) demonstrated that hoof strain was not different in magnitude between shod and unshod horses although strain distribution was different. Barrey et al. (1991) measured “shock and vibration [vertical deceleration] during hoof impact on different track surfaces” using hoof wall mounted accelerometers. Trotting on asphalt produced shock (peak deceleration, metres/second/second) 10x higher than on sand, wood fibre, wood chip and would be estimated to be 20x higher than on good grass going or a good arena surface. Willeman et al. (1999) then used accelerometers in the hoof, distal, middle and proximal phalanx and metacarpal bone in cadaver limbs to quantify transmission of vibrations in the distal forelimb. At the hoof wall, the amplitude was 15% higher in shod versus unshod but at the first phalanx and metacarpus the difference between shod and unshod vanished.
Unfortunately, there appears to be a dearth of published peer-reviewed information on barefoot management; a PUBMED search using the following terms [(barefoot or unshod) and (horse or equine or equidae or pony)] yielded only 24 citations. Only one of these (Hilary’s paper from 2011 (Effects of barefoot trimming on hoof morphology, Clayton et al. 2011, Australian Veterinary Journal) appears to deal specifically with barefoot management.
If you want to read more on this area can I suggest the excellent review by: Parkes and Witte (2015), The foot–surface interaction and its impact on musculoskeletal adaptation and injury risk in the horse in the Equine Veterinary Journal.