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Fit for Purpose?

For millions of years, horses have been breed selectively to produce an anatomy and physiology to run away fast and to cover many miles to find food. Anatomically, these adaptations include lengthening of the leg, reduction in the number of digits and loss of the collar bone. Physiological adaptations have enabled greater oxygen delivery to the muscles and a greater ability to use the available oxygen at the sites it is needed the most.

Improving performance and fitness in the short term
There is not a lot you can do to improve your horse’s anatomy as once it is an adult its leg length is not going to change, no matter how much training you do! However, both the physiological parameters and muscle mass can be adapted by training and endurance, which can be helped by a good knowledge of nutritional needs and training schedules.
In the short term, the best way to increase performance is a good warm up. This has the effect of raising the body temperature which increases the speed the enzymes can breakdown fuel reserves, increasing blood pressure (which has the effect of opening up blood vessels particularly in the lungs allowing better oxygenation of the blood), increasing the elasticity of the skeletal system, and increasing circulating plasma volume and circulating red blood cells, partly aided by the contraction of the spleen.

Longer term improvements
Training must be tailored to the discipline that the horse competes in. Obviously, to improve the performance of sprint horses we will need to work on improving maximal speed and increasing the anaerobic capacity of the muscles. In contrast, endurance animals will not need to train at maximal speed but need to increase the aerobic capacity of the body. For the muscles to adapt to training they need to be stressed and subjected to periods of hypoxia (periods of reduced oxygen), this will stimulate the genes to produce more enzymes and proteins. The most important part of any training schedule is adequate rest between strenuous exercises. This is just as important as the exercise itself and is often overlooked. For example, after using up glycogen (the stored energy source) in the muscles it can take 3 days to replace (although this can be faster by giving intravenous glucose infusions). It takes 10 days to repair muscle damage and 24-36 hours to replace any fluid lost due to sweating.

• Anaerobic fatigue
This occurs due to the breakdown of energy without the use of oxygen and is required in high power short sprints. As a by-product of anaerobic metabolism lactic acid is produced (this raises the pH acidity) in the muscles and blood which inhibits muscle contraction. The horse has a large capacity for absorbing lactic acid and can tolerate much higher levels than a human and this capacity can be increased by training. The measurement of lactic acid in the blood is a good indicator of levels of fitness and can be used as an indication of the success of your training regimes.
• Aerobic fatigue
This occurs when the amount of oxygen is sufficient but fuel reserves run out, supply cannot meet demand, and/or fluid/electrolyte loss is high enough to reduce the circulating blood volume. Training alters the body to allow more efficient release of fat reserves and the quicker conversion to usable energy for the muscles.

Signs of fatigue
• Reluctance to exercise.
• Muscle soreness.
• Extreme sweating.
• Decreased appetite.
• Decreased thirst.
• Flared nostrils for prolonged period after exercise.

If these signs are ignored or missed and work is continued without the proper treatment then it can lead to exhaustion.

Signs of clinical exhaustion
• Depression/distress/abnormal behaviour
• Increased rectal temp greater than 41‎°C
• Persistently raised heart rate greater than 60bpm
• Thumps (diaphragmatic flutter, looks like hiccups)
• Muscle fasciculation
• Colic
• Heart arrhythmias
• Dehydration

Clinical exhaustion can be a potentially life threatening condition, and recovery will take time and certainly put back any training schedule.
Avoiding exhaustion entails a combination of adequate fitness for the sport undertaken, early recognition of fatigue, and electrolyte supplementation before, during and after the event.

St David’s Equine Practice provide the equine veterinary services for Molecare Veterinary Services. www.stdavids-equine.co.uk

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