Now that winter is fast approaching! For the endurance horse, riders can use this winter to get back on track and have an exceptionally fit athlete ready for the spring events.

Endurance horses are extreme athletes. As in all athletic activity of long duration, feed and fitness must go hand in hand if the horse is to perform at his best. The goal for any rider or trainer in every equine sport is to have the horse compete in top form with minimal stress.

The aim of a feeding and conditioning programme is to provide fuel reserves for the working muscles and improve muscular efficiency.

During the fittening process the muscles, cardiovascular system, respiratory system, and neuromuscular co-ordination respond favourably to conditioning and while you may not be able to see the changes you will certainly see the results. A fit horse will not blow as much or tire as quickly when you are riding him, and his breathing and heart rate will return to normal more quickly after exercise.

Of all the body's systems, most is probably, known about how the muscles adapt during training. The extent of the alterations of the muscles during training are largely dependent on the pattern and frequency of nerve impulses arriving at the individual muscle fibres. Therefore one can only get a favourable effect from training if it entails the same type and intensity of exercise that will be encountered during competition. If the competition requires prolonged, slower speed exercise (aerobic) then the oxidative capacity of the muscles needs to be increased. Training also increases the availability of fuel to the muscle fibres by encouraging an increase in the number and size of the mitochondria within each muscle fibre. These mitochondria contain the enzymes responsible for the combustion of glucose and free fatty acids to produce energy molecules. As the horse gets fitter, in conjunction with the increase in the level of enzymes within the mitochondria, there is also an increase in the level of enzymes responsible for supplying and degrading free fatty acids before they enter the mitochondria. This results in more fatty acids being utilized, thus sparing the glycogen stores and delaying the onset of fatigue. In line with this increase in the capacity to utilize oxygen, there is also an increase in the number of small capillaries around the muscle fibres so that the increased oxidative potential of the fibres can be properly utilized. During periods of inactivity, a reverse effect of this increased oxidative capacity is observed.

Muscles require fuel to be able to function and therefore the nutrition of the horse is linked to his ability to perform. What you put in not only maintains body condition but also fuels the horse providing energy to the muscles for work. However, it is not just the amount of food that we put into a horse that is important, but also the type of food we provide. Exercise affects muscle fibre types in the horse and these muscle fibres have different contractile and metabolic characteristics, functioning under different conditions and using different fuels. Providing a diet containing alternative energy sources allows the muscles to use the most appropriate fuel for the work being done, helping to conserve precious glycogen stores. The horse has three basic muscle fibre types as shown in figure 1:

Figure 1

MUSCLE FIBRE TYPE	CONRACTION SPEED	ENERGY PRODUCTION
Type 1	Slow Contracting	Aerobic (uses oxygen)
Type 11	Fast Contracting	Mostly Aerobic
Type 11B	Fast Contracting	Anaerobic (absence of oxygen)

Different types of horses will have different percentages of muscle fibre types. (see figure 2)

Figure 2

PERCENTAGE OF SLOW TWITCH FIBRES IN DIFFERENT BREEDS
Thoroughbred	Standard Bred	Endurance Arab
13	18	28

The endurance horse has more slow twitch fibres so this may explain why the Arab excels at endurance riding.

The fuel or energy that you put in is a measure of the feeds potential to fuel body functions and muscle contraction through work. As it is not possible for horses to continually eat during exercise the energy from the feed must be stored within the body to be used later as a fuel for muscle contraction.

There are three main energy sources used by the horse. Fibre is the most important, and one that is all too commonly overlooked. As there is low enzyme activity in the saliva and in the small intestine for the digestion of sugars and starch, this suggests that the horse’s main energy source is not supposed to be sugars. The primary energy source should be volatile fatty acids produced through the fermentation of forage (hay, haylage and pasture) in the hindgut by millions of bacteria. The fatty acids are then used either directly as a fuel in the cells, or they are transported to the liver and converted to fat to strengthen the body’s fat stores and used for energy production later. The process is long and slow so fibre can be used as an energy source throughout an endurance event as the fermentation of fibre continues long after the meal has been eaten. The provision of fibre is also critical to the health of any horse as it maintains gut motility thus reducing the occurrence of colic. Fibre also helps to maintain water intake and acts as a reservoir to hold electrolytes and water therefore helping to prevent dehydration.

Fibre is hay, pasture and haylage but also includes products such as alfalfa, Soya hulls and sugar beet. These are superior to long fibre as an energy source because their low lignin content makes them more digestible. These are important ingredients found in commercially formulated endurance diets such as Enduro 100, and will play an important role in increasing the energy level in the diet of the endurance horse as the new competition season approaches.

If the hindgut is fed properly with good quality fibre, the nutrients supplied are sufficient to keep most horses in light to moderate work, but as you gradually increase the speed and intensity of exercise, forage alone will not provide sufficient fuel for the muscles to function properly without fatigue. Fats are extremely energy dense and contain up to 2.25 times more energy than the equivalent weight of cereal. Horses are able to digest fat extremely efficiently and the release of energy is slow making it an excellent energy source for horses doing prolonged low intensity exercise. Research by Pagan et al., 1987 showed that feeding fat to horses resulted in greater mobilization and utilization of fat during long distance exercise. Conditioning the horse to a high fat diet along with a sensible exercise programme takes approximately eleven weeks and results in improved enzyme systems to utilize fat, therefore sparing the use of muscle glycogen (it is actually now thought that it takes less than eleven weeks).

Starch is a carbohydrate that is composed of many glucose units linked together. Starch forms up to 50-60% of the cereal grain's dry matter. It is digested rapidly in the small intestine and broken down into glucose molecules, which are absorbed into the bloodstream and used to make energy (ATP) or is stored as muscle or liver glycogen for later use.

We receive many nutritional enquiries from people who confuse protein with energy. Protein is used for cell renewal, tissue and muscle repair. If it is fed in excess of requirements the horse is able to use it as an energy source but it is a very inefficient and energy consuming process. To produce energy from the protein molecule it is cut in half. The amino acids are converted to nitrogen in the liver and excreted as ammonia. One of the signs of horses being fed excess protein is the increased smell of ammonia in the stable. An endurance horse must have lungs in good shape so this is particularly detrimental to him. The remaining part of the protein molecule (the carbon skeleton) is then used to synthesize ATP or it is stored. Horses that are fed high protein diets are shown to have an increased demand for water, thus increasing the risk of dehydration. The ideal protein level for an endurance horse would be about 8-10% but this is difficult to achieve in the overall picture so care must be taken not to greatly exceed protein requirements.

So we have seen how the muscles adapt to use the fuel that they receive more effectively, and the types of fuel that they metabolise, but how over the winter can you influence your horse’s performance by manipulating his diet?

While your horse is walking its muscles will be contracting very slowly and Type 1 muscle fibres are recruited. These use predominantly fat as an energy source and the whole process takes place in the presence of oxygen (aerobic). Body fat stores are mobilized and the process is fast enough to support this level of exercise. As the work increases up to a trot and a canter, the Type 1 fibres are unable to contract fast enough to propel the horse forward so the Type 11A fibres are then recruited. These fibres use glycogen and fat as energy sources as glycogen can be metabolised very rapidly to produce energy quickly. Speeds above this level means that Type 11B fibres are employed and these produce energy in the absence of oxygen by a pathway called anaerobic glycolysis. The toxic by-product of this metabolic pathway is lactic acid and this causes muscle fatigue. Most of the time the endurance horse works aerobically and only during the sprint for the finish and climbing steep hills would the Type 11B fibres come in to action. The aim through the winter will be to increase fitness levels and plan to ride primarily below the anaerobic threshold, thus improving the utilization of fats as the primary fuel and therefore preserving glycogen stores.

Outlined below are two sample diets. The first diet would be suitable for the horse in light endurance work, while the second diet shows a ration that is currently being used at the Royal Stables in Abu Dhabi on endurance horses that are currently in intense competition. Notice how each diet has a large reliance on fibre.

Diet One:		Diet Two:
Endurance- Light Work Horse Weight 400Kg Age 10		Endurance-Intense Competition
Hay (Kg/day)	5.00	Hay (Kg/day)	6.50
Enduro 100 (Kg/day)	3.00	Enduro 100 (Kg/day)	4.5
		Fibre Mix (Kg/day	0.75

POINTS TO REMEMBER WHEN FEEDING THE ENDURANCE HORSE

• Feed plenty of good quality forage. This should form the basis of your horses diet and should not be fed below 1.5% of the horse’s bodyweight. Those horses that are carrying a little excess condition will not require additional hard food until they have lost the weight but they will require a source of trace elements. Forage will maintain intestinal health and act as a reservoir for water and electrolytes.

• Maximize access to pasture but take care not to poach your grazing and ruin it before the spring.

• As work increases additional energy may be required. Choose diets that are high in oil and digestible fibre e.g. Enduro 100.

• While starch is required as an energy source feed with care. Do not feed more than 5lbs in one meal to a 500kg horse. This will reduce the likelihood of causing digestive upsets caused by starch overload. Increase the grain concentrations of your horse’s diet several days before a long ride to make sure that the glycogen tank is full.

• If feeding low levels of concentrates make sure that the diet is fully fortified with trace elements. This can be done by using a feed balancer such as Bio-Life 2000. These products are designed to provide all the necessary trace elements when fed at low levels.

• A 500kg horse contains around 20kg of electrolytes and horses that are in hard work require more electrolytes as they have increased loss of them coupled with decreased absorption. Equine sweat contains around 40% Sodium, 40% Chloride, and 10% Calcium. Electrolytes such as Endura Max will restore the key electrolytes relinquished in the sweat and can help to prevent metabolic disorders such as thumps and Tying Up.

• Consider using a yeast and probiotic to maintain maximum intestinal health and function. These may also help to boost the immune system and reduce stress levels.