Date: [__date__]

Dear [__name__];

An excellent study published in the Journal of Applied Physiology in October 2009 on post exercise fluid and electrolyte supplementation inspired this month's discussion on how horses recover from exercise and how we can help them recover better, faster and thus improve their performance in the competition arena.

Practice news
Mike Tweedie represented the practice as the FEI Veterinary Delegate at the 2010 Dressage and Jumping with The Stars held at Werribee in March. Mike enjoyed the weekend and commented that it was a pleasure to officiate at such a well run event.

Carbohydrate (CHO) metabolism
The horse is an amazing athlete and optimum performance in competition is dependent on the availability of metabolic fuels like skeletal muscle glycogen to provide the building blocks of ATP production and facilitate muscle contraction during vigorous exercise.

Vigorous exercise for short periods and prolonged submaximal exercise are associated with decreases in muscle glycogen reserves in horses and man. Resynthesis of muscle glycogen stores requires 48-72 hours in horses compared with less than 24 hours in man. Horses that are exercised frequently or undergo several warm-ups may have low glycogen stores that persist at the time of subsequent exercise. Examples that come to mind include racehorses that are required to back up after a race for their next start within 7 days or showjumpers that compete in multiple rounds over a number of days.

Now, why are horses so different to man when it comes to skeletal muscle glycogen resynthesis? Part of the answer may lie in the way that horses digest carbohydrates (CHO). CHO is stored within the body in the form of skeletal muscle glycogen. As hindgut fermeters, horses digest soluble CHO in the small intestine, whilst non-soluble CHO passes through the small intestine and undergoes bacterial fermentation in the hindgut.

Unlike humans, horses have a very limited ability to digest soluble CHO. For example, in humans a daily CHO intake of 7-10 g/kg bwt per day results in a marked increase in skeletal muscle glycogen. The equivalent intake for a horse would have to be between 6.5 and 9kg of oats per day. So, whilst horses will gradually adapt to a diet higher in soluble CHO over time, and whilst we do feed high grain diets to horses performing at elite level, feeding horses very large amounts of soluble CHO is not recommended due to the increased risk of causing health problems such as laminitis, colic, gastric ulcers, tying up and insulin resistance. Therefore, simply carbohydrate loading horses after exercise is not an efficient or practical strategy to increase resynthesis of skeletal muscle glycogen.

Dehydration
It is commonly observed, and generally accepted that dehydrated horses will not eat. Considering that the intensity of exercise that results in skeletal muscle glycogen depletion, generally results in dehydration as well, it becomes obvious there is a real danger that horses performing at elite level can easily become stuck in a cycle of dehydration and inappetence post competition that can result in an overly prolonged recovery period.

There is also some evidence that dehydration affects glycogen synthesis and that cell shrinkage associated with dehydration is associated with an increase in glycogenolysis (splitting of glycogen to provide a rapid supply of ATP for muscle contraction). Horses produce a electrolyte rich sweat that results in an isotonic to hypotonic dehydration, unlike humans which produce a dilute sweat that results in a hypertonic dehydration. Unfortunately, exercise induced dehydration in horses does not stimulate the same thirst response that it does in man. Perhaps this is basis for the old saying; ‘you can lead a horse to water but you cannot make it drink’!

Water and potassium are required by cells to synthesise glycogen, so prolonged, exercise induced dehydration may be another part of the reason why muscle glycogen replenishment is so slow in horses. Water alone is not effective in restoring hydration and the importance of replacing electrolytes lost in sweat is clear.

This generally accepted fact formed the basis for a study that hypothesised, administering 8L of hypotonic electrolyte solution via nasogastric tube followed by a ad libitum water and normal hay/grain meal to a group of horses after a controlled exercise test would enhance the rate of muscle glycogen synthesis compared with a control group that were given access to only plain water with their normal hay/grain meal.

Researchers took biopsies from the gluteus medius muscles and collected blood from both groups of horses and indeed found that administering 8L of hypotonic electrolyte solution resulted in faster rehydration and a faster rate of muscle glycogen synthesis compared with control horses.

The findings from this study support the theory that post exercise dehydration is an important part of the reason for slow muscle glycogen resynthesis in horses compared with other species. This study highlights how important post exercise rehydration strategies should be to the management of our elite horses. Replenishing fluids and electrolytes after fatiguing exercise is a simple, effective and low cost strategy that will help our elite animals recover in the fastest and most effective way possible.

Please do not hesitate to contact the practice if you would like to discuss the most practical way to implement electrolyte and fluid supplementation into your management program.

Waller, A. P., Heigenhauser, G. J., Geor, R. J., Spriet, L. L. and Lindinger, M. I. (2009) Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances glycogen resynthesis in Standardbred horses. J. appl. Physiol. 106, 91-100.