Author Name: Katie Salter, BSc (Hons) Equestrian Sport Science
Horseracing has always had a high injury rate. Some of the key factors influencing injury rate are training regimes, surface type, horse age and type of race. Research has shown that different surfaces can induce different loads under racing conditions increasing fracture rates. Exercise can have a positive effect on young horses by increasing tendon cross section area and reducing fracture rates later in life. Exercise at a young age can also have a negative effect though, via causing osteochondrosis and having a damaging effect on the growth plate due to the rapidly growing skeleton being unable to adapt appropriately under vigorous training. Training regimes have seen changes over the years with the popular use of uphill/incline exercise becoming standard practice alongside lack of rest and recovery. This has increased fracture and hindlimb lameness rates. Studies have suggested that this is due to an increase in strain placed on the limb. A larger number of injuries were also seen in national hunt races in comparison to flat races, which was due to either a collision or a fall at a fence. Horserace Betting Levy in the UK are funding research into factors affecting injury rates and what can be improved to decrease fatalities. Using the findings of this research, it is then hoped that initiatives can be set up to help tackle the ongoing issue of equine racing injury.
Injury rates in racehorses are a major welfare concern. In Britain, 90% of injuries involve the horse’s limb (Perkins, Reid and Morris, 2005). This can cause lameness which is a significant welfare issue (Dyson et al. 2008). Furthermore, joint injuries are observed in 24% of UK Thoroughbreds with the carpal, metacarpophalangeal and metatarsophalangeal areas being worst affected due to repetitive loads (Reed et al. 2012). Per month 1.15 out of 100 UK flat racehorses in training are reported to have fractures (Verheyen and Wood, 2004). Fractures can be due to excessive repetitive high speed, high intensity over loading, cumulative distance training or external trauma, which can all result in micro-damage (Verheyen et al. 2006; Dyson et al. 2008; Martig et al. 2014). Out of 616 flat racehorses assessed, 248 injuries were recorded, with fractures of the tibia (20.7%) and proximal Phalanx (14.5%) being the most common (Ramzan and Palmer, 2011). National hunt racing sees more musculoskeletal injuries with 89% being the superficial digital flexor tendon (Ely et al. 2009; Clegg, 2012).
Training regimens, which differ between yards, remain one plausible factor that influences injury rate due to varying surfaces, frequency of high speed exercise and differing rest periods (Woodward et al. 2000; Boston and Nunamaker et al. 2000; Verheyen et al. 2006). It is hard to distinguish if this is due to a trainer’s personal preference or lack of knowledge though. Misunderstanding the bone remodelling process for instance could, lead to fatigue stress fractures (Riggs, 2002; Verheyen et al. 2006; Dyson et al. 2008; Ely et al. 2009; Martig et al. 2014). Further factors related to injury rates are longer distances and increase in speed, race frequency and the experience and age of the racehorse (Pinchback et al. 2004; Martig et al. 2014). In addition, similarly to as is seen in sports horses, training young horses, ground conditions and excessive workload increase injury (Dyson, 2002). Firmer surfaces have also been associated with higher risk of fatal injury (Williams et al. 2001; Verheyen and Wood, 2004; Perkins, Reid and Morris, 2005). Studies have found that differences between turf and all-weather surfaces (inclusive of surface material, gradient, maintenance and season) influenced the way of going, resulting in the perceived injury rates (Williams et al. 2001; Dyson et al. 2008; Martig et al. 2008; Ramzan and Palmer, 2011). Differing injury rates and types, which have a significant impact on the horse’s welfare, will be discussed during this review to try to determine the factors influencing catastrophic injuries (Perkins, Reid and Morris, 2005). One of the most comprehensively researched areas related to injury is track surface (Reiser et al. 2000; Firth and Rogers, 2005; Setterbo et al. 2009).
2.0 Critical Review
2.1 Influence of track surface on racehorse injuries
All-weather, synthetic surfaces have become popular alternatives for training, enabling all year round preparation (Dyson et al. 2008). Synthetic surfaces have low peak accelerations, peak ground reaction forces and reduction in concussion. These are all factors thought to decrease musculoskeletal associated fatalities (Setterbo et al. 2009; Jacob et al. 2009; Symons, 2016). However, a sudden change in loading environment when under racing conditions, such as ploughed dirt and turf, alters loading forces through bones increasing fracture rates (Kohnke, 2007; Carke, 2009). Supporting research found that horses training on sand during their first year had an increase in fatal fractures during racing (Parkin et al. 2010), although previous research states that these injuries could be due to other influencing factors, such as training at lower speeds or being predisposed to injury (Perkins, Reid and Morris, 2005). Data from a computer system designed by Japan Racing Association to enable the exchange of racing information was used to look at 183,465 flat racehorses, racing on 99,803 turf courses and 83,662 dirt courses at ten different racecourses (Maeda et al. 2011). The validity is questionable as Maeda et al. (2011) did not report the amount of data excluded due to disqualification and any human error in updating due to inaccurate or incomplete information. It was found that the track condition and type had an effect on speed. Horses were found to gallop faster on dirt tracks; however, as conditions deteriorated, their speed decreased and they found it harder to run on a sloped track than a muddy track (Maeda et al. 2011). Velocity on grass (9.06, SE 0.292 m/sec), is faster than on sand (7.90, SE 0.132 m/sec) (Rogers and Firth, 2004), which increases the excitement of spectators. Faster going increases injury risk such as epistaxis and distal limb fracture increasing concerns for equine welfare (Rosanowski et al. 2017). The data by Maeda et al. (2011) could be assessed further by analysing data from other countries due to the variation in track conditions caused by differences in weather (Williams et al. 2001). Weather conditions have been seen to play a significant role in the ground conditions (Perkins, Reid and Morris, 2005). Firmer going can cause an increased risk of injury (Mohammed, Hill and Lowe, 1991; Pinchbeck et al. 2004; Reardon et al. 2013). New Zealand in winter is associated with a reduction in the odds of injury due to higher moisture contents (Perkins, Reid and Morris, 2005). This suggests that regions of low rainfall increase fracture associated fatalities due to structural changes within the track surface (Williams et al. 2001). In Symons (2016) study, horses had greater fetlock hyperextension or dorsiflexion and reduction in forces to the tendon and ligaments during gallop on synthetic surfaces compared to dirt tracks. Synthetic surfaces reduce musculoskeletal failure through changes in distal limb motions due to different race surface mechanics altering musculoskeletal tissue loads, and predisposition for injury (Symons, 2016). The validity of this study is debatable however because only 5 horses were used, there was no repetition of the test and the surface was only harrowed prior to testing. The key aim for the British Horseracing Association is to improve racehorse welfare (BHA, 2018). Therefore following changes seen in other disciplines; a shift towards synthetic surfaces would be beneficial in racing (Hobbs et al. 2016).
2.2 Influence of training on racehorse injuries
A high number of injuries occur in training due to insufficient recovery periods after chronic fatigue states from training or racing. This results in inadequate recovery and depletion in energy stores leading to poor performance, fatigue and exhaustion (Evans, 2017). Inadequate rest and excessive overloading results in an increase in matrix and mineral deposition, greater activation of osteoclastic resorption and overlaying of cartilage, increasing brittleness and accumulation of micro-damage in bones (Norrdin, 1998). Repetitively increasing loads exceeding the rate of bone adaption which can take place can result in a rise in the process of ossification leading to dorsal metacarpal disease and stress fractures (Bailey, 1998; Lawrence, 2003b; Davies, 2003). Similar overloading-induced reactions are seen in racing greyhounds when exercised at high speed and high frequency at young ages (Boemo, 1998; Ireland 1998).
Ramzan and Palmer (2011) observed that tibia stress fractures are the most common in flat racing. However previous studies reported third metacarpal, pelvis and carpal fractures to be more common (Bathe, 1994; Verheyen and Wood, 2004; Cogger et al. 2008). Differences may be due to excessive use of uphill training in the Ramzan and Palmer (2011) study. Yards are now using an increase in incline which can increase the risk of hindlimb lameness (Dyson et al. 2008). Incline is thought to produce larger peak forces, greater stride frequency and compression which is usually found to be unilateral (Pieter and Ramzan 2014). Ramzan and Palmer (2011) found that hindlimb stress fractures were the most common injury type. This was also seen in a study looking at high intensity training regimes, which found hindlimb locomotion asymmetry increased during spring when the 2-year-olds training commenced (Ringmark, 2016). A subjective score to measure lameness was utilised; therefore the results may not be reliable so a more objective measure would increase reliability (Ringmark, 2016). Ramzan and Palmer (2011) also reported that 25% of horses in training each year sustained a significant musculoskeletal injury. This study excluded dorsal metacarpal disease though which is an explanation for a higher percentage reported by Cogger et al. (2008).
Two flat yards in the UK observed 291 horses over one year and found 18 fractures occurred in training (Verheyen and Wood, 2004). Validity is questionable though as the study was only conducted on two flat yards; however other studies have reported similar findings (Verheyen and Wood, 2004). A two year study on fracture rates in training found 245 fractures occurred in training in Newmarket (Bathe, 1994). These rates were not just seen in the UK. Throughout California, 100 horses in training over one year were euthanized (Blackwell, 2011) and in 9 months there were 71 fatal fractures in training, compared with 66 during racing (Estberg, 1995; Verheyen and Wood, 2004).
It is important to simulate more realistic demands of racing to create a more representative adaption response without having a detrimental effect (Verheyen et al. 2006). The average gallop is around 60km/h however it is essential not to exceed this, as extreme loading and increased limb cycles result in accumulation of micro-damage, increasing fracture risk (Verheyen et al. 2006; Martig et al. 2014). Although no gallop work during training within the first year was associated with an increase in injury risk (Parkin et al. 2008), inappropriate preparation for competition resulted in earlier fatigue during racing, increasing injury risk and exhaustion (Evans, 2007). A minimum distance gallop of 805-2012m per week was thought to decrease fracture rates (Parkin et al. 2008). Variation of exercise intensity was found between yards; some include six days canter work and a gallop 2-3 times per week (Verheyen et al. 2006), whereas others are thought to not include gallop work during their normal training regime. The use of bone scintigraphy and ultrasonography in 3 month intervals during training would be a useful method to track the remodelling process and evaluate information as well as increasing early recognition of injury (Verheyen et al. 2006; Ely et al. 2009; Clegg, 2012).
2.3 Effect of horse development in racing
National hunt racehorses begin training at 3-4 years, whereas flat racehorse training starts at 18 months (Ely et al. 2009). The age at which a horse should start training is debatable as age has been found to have both positive and negative impacts (Williams et al. 2001; Dyson et al. 2008). Firth (2006) found that the cross sectional area of the third metacarpal (MC3) was significantly larger and bone mineral density was higher in foals at pasture compared to stabled foals. Proximal sesamoid bones and trabecular bone mineral density were higher in exercised foals. Differences between groups disappeared at 11 months of age though, suggesting normal development continued once out on permanent pasture (Firth, 2006). There were indications that sprinting led to overstimulation of bone resulting in less active mineral deposition long-term. One explanation is the horse’s lack of skeletal maturity to withstand training (Williams et al. 2001; Dyson et al. 2008), although there is evidence that exercise has benefits for the immature skeleton and reduction of fractures later in life (Ely et al. 2009). The foals which did perform sprint exercise appeared to have greater MC3 cortical size and mineral content (Firth, 2006). This study did not investigate horses after the age of 11 months however it suggested exercise is beneficial (Firth, 2006). This suggestion is supported by evidence showing that early training is associated with an increase in the cross section area of tendons and greater thickness of hyaline cartilage (Rogers and Firth, 2005; Firth, 2006). In contrast, high frequencies of high speed exercise were discovered to have detrimental effects on bone adaptation (Judex and Zernicke, 2000). This causes osteochondrosis, trabecular micro-fracture and retained cartilage and affects the growth plate (Firth, 2006).
In 2001, 537 horses entered flat racing training for the first time. Only 61% went on to race as 2 year olds and of those unable to continue onto racing 62% required veterinary interventions (Wilsher et al. 2006; Dyson et al. 2008). Supporting research showed that horses starting intense training at 2-3 years showed a higher risk of joint injury (Reed et al. 2012), shin soreness (Perkins, Reid and Morris, 2005) and an inability for the rapidly growing skeleton to adapt appropriately under vigorous training (Dyson et al. 2008). Horses are 90% of their mature height and 66% of their mature weight when they reach 12 months (Firth, 2006). Maturity in thoroughbreds is around 2 years, however full growth is not complete until 4 years (Firth, 2006). The approach used by national hunt trainers that allows their horses time to adapt skeletally and provides more rest periods than flat trainers is beneficial (Verheyen and Wood, 2004). This was found to reduce micro-damage, limit fatigue accumulation and allow appropriate bone adaptation to take place (Verheyen and Wood, 2004). By reducing the magnitude of the loads generated within the limb and the number of cycles, it enables the body to repair and adapt thus decreasing injury risk (Martig et al. 2014), whereas it was seen that flat racehorses have a shorter racing career (Verheyen and Wood, 2004).
There are suggestions that as horses get older there is a decreased tendon matrix (Smith et al. 2002). Research has found that older horses were more susceptible to injury due to the inability to remove partially degraded collagen from the matrix leading to reduced mechanical competence (Clegg, 2012). Ageing decreases adaptive bone responses and increases the occurrence of injury, in particular increasing the risk of tendon and ligament injury (Verheyen and Wood, 2004; Perkins, Reid and Morris, 2005; Reardon et al. 2013; Rosaowski, 2017).
2.4 Injury rates in race type
The frequency of injury is higher in national hunt racing than flat racing (Williams et al. 2001) with fatality rates of 3.0/1000 starts associated with obstacles (McKee, 1995). Injuries to the shoulder/Humerus region (1.29/1000 starts) were commonly associated with a fall at a fence (41%) or a collision with a jump (78% at a hurdle and 47% at a fence) (Williams et al. 2001; Ely et al. 2009). It was reported that horses being whipped progressively throughout the race were 7 times more at risk of falling (particularly at a fence) compared with those not being whipped (Clegg, 2011). The use of the whip has been controversial as it causes a flight response, increasing speed which is associated with increased fall rates, which can compromise welfare (McLean and Mcgreevy, 2010). Whips are used to reduce drifting and collisions and the British Horseracing Authority have rules in place to monitor usage to protect horse welfare (Aid, 2016). Jockey experience was also linked to falls and injury rates. Inexperienced jockeys approached fences differently (Powers and Kavanag, 2007; Kang, 2010) and it was found that 68% of horses with tendon injuries completed the race before the injury was detected (Ely et al. 2009), although it was suggested that the horses’ adrenaline may mask an injury (Sukumarannair et al. 2002).
Injuries in the racing industry are a major welfare concern. Investigations into the effect that surface, age, training regimes and race type have on injury rates have been conducted, with fractures, tendon and musculoskeletal injuries being found to be the most common injuries. Research can help tackle misconceptions used in training as several studies have shown major effects of differences amongst trainers. The effect of race type is another key influencing factor with the frequency of injury seen to be higher in National Hunt racing than flat racing. Age is undoubtedly an important factor affecting injury rates although it is an area which needs to be investigated further as evidence from previous studies have been controversial. Shifts towards synthetic surfaces, particularly in training and other disciplines, need further consideration for the use on racing tracks to help minimise injury. Further studies need to be conducted to enhance understanding of racehorse injuries and ways to reduce injury rates to improve equine welfare.
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