THE ARVS is a not-for-profit organisation with over 800 members. At the meeting a number of speakers gave presentations looking at ways to reduce the risk of injury in racehorses. A lot of the information is also applicable to high performance horses.

The majority of injuries suffered by racehorses, in training or on the racetrack, are musculoskeletal injuries, such as bone fractures or chips, and soft tissue injuries. This has a financial and welfare impact on all involved in the sport. Research and studies are ongoing in an effort to reduce injury risk. Respiratory health problems are another common cause of poor performance in racehorses.

This is a complex subject and, after a day of highly informative presentations, there were still probably as many questions as answers. However, it provided a greater understanding of how and why injuries occur and the main risk factors. This information should help owners and trainers make informed decisions about the training and general management of their racehorses.

EXERCISE PHYSIOLOGY AND RESPIRATORY HEALTH

Dr Shaun McKane (Cotts Equine Hospital) highlighted how effective and well adapted a healthy horse’s cardiopulmonary (heart and lung) function is. Racehorses have exceptionally high cardiopulmonary function for their body size.

The maximum heart rate and stroke volume for a 500kg horse during exercise is 210-240 beats per min and approximately 1.6 litres respectively. Their maximum oxygen consumption (VO2 max) exceeds 160 ml, double that of most elite human athletes and demonstrates the exceptional aerobic capacity of the thoroughbred horse.

The equine lung has a surface area of diffusion 2.5 x greater than other animals. A human athlete’s air intake is approximately 4 litres, in a galloping horse it is 38 litres. At rest a horse takes about 12 breaths per minute, inhaling 5 litres of air per breath, giving a ventilation rate of 60 litres. A galloping horse can take up to 120 breaths per minute, inhaling 15 litres of air per breath which increases its ventilation rate to nearly 2000 litres per minute. This massive capacity puts the lungs under immense pressure, explaining why even small problems can have a big impact on performance. Good respiratory health is vital for the horse to function at maximum capacity.

Oxygen is inhaled and carried through the bloodstream to the muscles where it is turned into energy. To maintain exercise for more than 30 seconds there must be a constant supply of oxygen to the exercising muscles.

When exercised the horse’s heartbeat increases from 30bpm to 240bpm. Cardiac output increases from 35 litres per minute to 300 litres per minute. Exercise increases the horse’s blood temperature, warming the muscles and allowing more oxygen to be offloaded to the muscle. Exercise lowers blood pH, making it more acidic, and increasing the concentration of carbon dioxide in the tissues, all of which allows more oxygen to be released to the muscles.

The lungs and circulation system of the horse act as a turbo charger. When a horse is galloping, everything is working at maximum, there is no reserve. The healthy horse has a highly effective turbo charger but to work at maximum capacity it relies on maximum oxygen intake. Capillary density within the muscles increases in response to exercise and decreases when exercise stops. A horse can change his muscle type in response to training, increasing the amount of type two, high oxidative, muscle fibres.

Mitochondria (structures within each cell) are the combustion chamber turning oxygen into energy. The rate of oxygen delivery and the number of mitochondria determine the quantity of power produced. Any compromise of the respiratory system will compromise the horse’s performance.

There are two main aspects to maintaining the maximum capacity of the respiratory system. The first is training the horse to achieve maximum oxygen consumption (VO2 max) and the second is minimising inflammation of the respiratory system.

TRAINING FOR VO2 MAX

Oxygen uptake in the untrained horse is 80ml/kg/min. In the trained horse it increases to 180ml/kg/min. Correct training increases VO2 max and controlling inflammation of the respiratory system will preserve VO2 max.

To make maximum use of a horse’s respiratory reserve the performance of the musculoskeletal and cardiovascular systems has to be increased and adapted through correct training. Long slow work strengthens muscles, while high intensity interval training is needed to increase VO2 max. Short bouts of fast work stimulate the necessary changes in muscle composition and oxidative capacity. Gradually increasing the exercise load is the key to increasing VO2 max.

The biggest increases in exercise load should take place in the first six to eight weeks of training. Speed and distance should be increased every 10-14 days to ensure the cardiovascular and musculoskeletal systems continue to adapt to the work load. After the first few months of training only minimal increases in VO2 max can be achieved. Three gallops over a distance of 400-600m, at a heart rate of over 150bpm, twice a week, is generally sufficient to maintain VO2 max. Each horse must be trained within his own abilities, some will respond to training faster than others. Careful monitoring is necessary to balance the need to increase fitness, with the risk of incurring injury.

HOW TO REDUCE IRRITANT EXPOSURE

  • Good ventilation, high ceilings and open windows in stable blocks
  • Maximum turnout time
  • Use minimal dust bedding
  • Do not muck out while the horse is in the stable
  • Feed steamed hay or haylage and give all feed and forage at floor level
  • Damp down central passages before sweeping
  • Muck out horseboxes and lorries and use minimal dust bedding when travelling to soak up urine
  • Be aware of horse asthma, particularly through March to May, from fungal spores and pollen
  • Nebulisers can be effective in managing inflammation.
  • Ensure vets properly disinfectant endoscopes between horses
  • Use a tracheal wash to determine if the horse is fit to run. Evaluating tracheal wash findings and making the decision, if necessary, not to run, may well save the horse from suffering a severe bleed

    • These are not new findings but serve as a timely reminder of the extraordinary effectiveness of the horse’s respiratory system when healthy. Prevention is better than cure and keeping the respiratory system healthy entails eliminating or minimising inflammation. Apart from the likes of pollen, we can do something about all of the measures discussed to help reduce dust and irritants in the horse’s environment. They are within our control, we just have to make them a priority in our management regime.

    PREVENTING INFLAMMATION

    Airway inflammation will affect a horse’s performance and increases the risk of exercise induced pulmonary haemorrhage (EIPH). Bleeders graded three or more out of four (200mls plus of blood) will be performance compromised.

    Inflammation can be caused by infection (viruses and bacteria), allergic reaction (to pollen, mould, fungi, dust, bacterial toxins) and by irritants (ammonia from urine, fine dust and even cold air).

    Bleeding (EIPH) is another cause of inflammation and upper airway obstruction will also impact on performance as it restricts oxygen intake. In younger horses, bacterial infection is more common than viruses or allergies but, in older horses, allergies tend to be the biggest culprit. Reducing exposure to irritants is one of the easiest forms of management.

    NATIONAL HUNT TRAINING AND OCCURRENCE OF INJURY

    Kate Maxwell presented a review of the most recent research looking at training regimes and the incidence of tendon and ligament injuries and fractures. There has been little research into racehorse exercise regimes. Some of the studies conducted have looked at the effect of cumulative canter and gallop distances in training regimes.

    When horses are trained with a heart rate of 140 beats per minute or below their respiratory system functions aerobically, with the blood supplying oxygen to the cells. The horse can continue working at this pace for long periods without fatigue. When exercising at over 150bpm lactic acid is released into the muscles, the horse tires and the respiratory system starts functioning anaerobically. Anaerobic respiration cannot continue for any great length of time. Long distance low speed work increases the horse’s aerobic capacity, and high speed work increases his anaerobic capacity.

    In shorter distance flat races, around 33% of the energy supply is aerobic, while in longer races, over 70% of the energy supply will be from aerobic metabolism. The training regime for National Hunt horses involves high cumulative canter distances, interspersed with fast work days.

    Interval training improves both aerobic and anaerobic performance, it allows a greater quantity of training to be performed at heart rates of over 200bpm. At this level of exertion beneficial metabolic changes are achieved. It also decreases the distance the horse has to gallop, which has been shown to be beneficial in reducing injury risk. Interval training also improves VO2 max, the cardio-respiratory system and the ability to remove lactate from the muscles which will delay the onset of fatigue.

    One study (K.Verheyen et al) collected data from 14 National Hunt or dual-purpose training yards over two seasons, involving 915 horses and 5228 races.

    Canter, gallop and race distances were recorded for all horses. It found that longer canter distances accumulated in the 30 days prior to a race, increased the odds of winning and winning prize money.

    A second study, of purely flat horses, found that cumulative high speed exercise (gallop and race) increased the odds of winning and winning prize money.

    Another study (E.Ely) looked at exercise regimes and risk of fractures, and tendon and ligament injuries (TLI). Data was collected from 1223 National Hunt horses in 14 yards over 18 months. An average of 1.1 fractures and 2.0 TLI per 100 horses/month were recorded. See panel 1 for findings.

    FINDINGS (panel 1)

  • Longer training distances on woodchip surfaces were associated with increased risk of TLI and fractures.
  • Longer training distances on synthetic surfaces were associated with increased risk of TLI.
  • Longer training distances on uphill inclines increased TLI and forelimb fracture risk
  • Accumulating longer distances around a bend was associated with increased risk of inside limb fracture.

    • DOES JOINT MEDICATION INCREASE THE RISK OF FRACTURES

    Lewis Smith, from Rossdales Equine Hospital, Newmarket, presented the findings from his research paper which looked into whether or not there was an association between joint injections and the risk of fracture. The study involved 1488 racehorses that had received joint injections. See panel 2 for findings.

    FINDINGS (panel 2):

    Horses that had received more than three previous joint injections were at increased risk of sustaining a fracture (of any kind, but mainly chip fractures) within 56 days of medication.

    Horses that received their first joint injection at an older age, had a reduced risk of sustaining a fracture within 56 days of medication.

    There was an association between injecting the knee and the risk of sustaining a post medication knee fracture (mainly chip fractures).

    There was NO association between injecting the fetlock and the risk of sustaining a post medication fetlock fracture.

    The study was somewhat limited because it was not possible to compare the findings to a control group of horses who had not received any joint medication. In the discussion that followed the presentation there were some suggestions that joint medication is not always the best option.

    Lameness associated with a joint can be a sign that the horse is not coping with the stress/load being placed upon him. If the joint pain is due to bone micro damage, then either resting the horse, or reducing the load is the answer. Medicating the joint will allow the horse to continue to be trained but it will not have removed the cause of the lameness. If the joint continues to be subjected to the same loads further damage will be accumulating and there is an increased risk of serious injury.

    Recent research has shown that in cases of horses suffering from POD (Palmar Osteochondral Disease – where the overlying cartilage of the subchondral bone becomes damaged), light work is better than complete rest. When a horse is completely rested there is an increase in the amount of bone being resorbed, and this can lead to joint surface collapse.

    Keeping the horse in light work will prevent complete deadaptation of the musculoskeletal system.

    USE OF MRI

    Mike Shepherd, Rossdales Equine Hospital, explained the benefits of using MRI to give a true picture of hard to diagnose lameness. MRI provides an accurate diagnosis of the injury and allows a better informed prognosis to be made. This was demonstrated with various case studies in which MRI had allowed for better decisions to be made on how to progress with each case. In some instances it may show that surgery is required. However, this early intervention will prevent a more serious, and possibly fatal injury occurring.

    MRIs may show that the injury seen is now inactive and that the horse can be trained on. In brief, it can help to prevent fatal injuries by early intervention, prevent unnecessary days out of training and prevent unnecessary treatment.

    In part two musculoskeletal injuries, one of the most commmon injuries in racehorses, will be addressed.