In order to answer the question, what can I feed my horse to give them more oomph, I’m afraid we need to do a quick recap on how the horse turns food into energy. Sorry this is the science bit 😊
The muscles and energy production
Energy generation is the process of converting stored chemical energy into mechanical energy for muscular movement. The basic unit of energy is Adenosine Triphosphate (ATP) and the main sources of energy are carbohydrates and fats which are broken down to yield ATP. Fats are stored in the muscle fibres and in the adipose tissues throughout the body. The breakdown of fat to yield energy can only take place with a constant supply of oxygen known as aerobic metabolism. Because oxygen is required the energy production process is slower but can be sustained for longer, meaning fat is an important energy source during low to moderate intensity exercise sustained over prolonged periods of time such as in endurance. Carbohydrates are broken down into glucose units in the small intestine where they are absorbed into the blood (blood glucose) and then either oxidised directly to produce ATP or stored in the body in the form of glycogen. The majority of glycogen is stored in the muscle cells and the remainder is stored in the liver. Muscle glycogen is an important fuel for energy generation during exercise.
For anything more than a slow canter the horse primarily relies on the glycogen stores in the muscles to produce energy. Glycogen can be broken down to produce energy either with or without oxygen. The process of energy production without oxygen is known as anaerobic metabolism. Anaerobic metabolism produces energy rapidly but also results in the production of lactic acid which, if too much accumulates, causes fatigue. This means it can only be used for short periods of time. Aerobic metabolism is not as fast but is very efficient at generating energy, producing up to 20 times more than anaerobic metabolism.
The left hand circles represent the process of aerobic metabolism. The right hand circle represents the process of anaerobic metabolism.
At rest the horse is getting the majority of its energy from fats and only around 15% of the circulating blood volume is being distributed to the muscles (during intense exercise the working muscles can receive up to 85%). At the onset of fast exercise the delivery of oxygen to the muscles does not immediately reach the levels required to support aerobic metabolism. During this period (30-45 seconds) the deficit in energy production is met by anaerobic metabolism of the glycogen stores in the muscles. It’s one of the reasons warming up is so important to prepare the body for the work to come. It ensures the muscles receive a steady supply of oxygen to convert both glycogen and fat into energy for muscle contraction and to replenish the glycogen stores used up in the initial phase of activity. Glycogen depletion causes fatigue and the better able a horse is to use fats in preference to carbohydrates as fuel, the longer it can delay the onset of fatigue. The result of fitness training is that the horse’ body gets better at transporting oxygen to the muscle, using it there to produce energy and thereby delaying the onset of fatigue.
The type of work determines where the horse gets its energy (or fuel) from
The work we do with our horses can be divided into 3 categories based on how the horse derives the energy to fuel it:
Low intensity, long duration work lasting 2 hours or more where aerobic metabolism is required to provide a continuous energy supply over a long period of time such as in endurance. Or short duration events where the exercise intensity is low or moderate such as dressage or showing.
Moderate intensity, medium duration work where exercise is strenuous but doesn’t exhaust or there are intermittent bursts of high intensity exercise such as jumping. This requires both aerobic and anaerobic energy production.
High intensity, short duration work where there is a primary sprint component requiring quick acceleration or top speed over short distances such as racing or polo. This type of work relies heavily on anaerobic metabolism.
Interestingly horses use less energy per km in canter than in trot and the least efficient gait is the walk which uses the most energy per km. This is the reason why walking is good for reducing weight because its primary energy source is the aerobic metabolism of fat. In general walking, trotting and slow cantering (HR of around 70-140bpm) will result in significant utilisation of fat. At heart rates around 140-190bpm (fast canter) the horse will be using a mixture of aerobic and anaerobic metabolism to generate energy from fat and glycogen. At heart rates of 200bpm (galloping) the horse gets the majority of its energy from anaerobic metabolism and will be producing lactic acid as a by-product. Research by Kentucky Equine Research shows that lactate accumulation remains low until heart rates reach approx. 180bpm (roughly 80% of maximum heart rate) and increases exponentially as heart rates near the maximum levels of 220bpm.
What do I need to know about lactate accumulation?
Lactic acid or lactate is a waste product of anaerobic metabolism. During low intensity exercise most of the energy requirement is met aerobically. As the exercise intensity increases, so too does the contribution of anaerobic metabolism to energy production. During high intensity exercise, lactate is produced faster than it can be removed and it starts to accumulate in the muscles. Since lactate is acidic it reduces the pH within the muscle fibres which slows the chemical reactions responsible for energy production. Lactate removal from the muscles is important for the horse to recover from fatigue and can take around 3 hours if the horse is rested. This time is significantly reduced if the horse is kept moving for 10-15 minutes after strenuous exercise. Hence why a cool down period is so important.
Training enhances the muscles’ ability to use fats to produce energy leading to a glycogen sparing effect. It also results in greater glycogen storage capacity in the muscle which is useful because fat can only be used as a major source of fuel when the exercise intensity is low to moderate. Being able to store more glycogen means that glycogen depletion and the resulting fatigue is reduced or delayed. In other words, the horse gets better at producing energy aerobically allowing it to go further at a given speed or to go faster over a longer distance without tiring.
Why do I need to know about Muscle fibres?
Most muscles in the horse contain a mixture of fibre types which each function slightly differently. There are 3 basic types - type 1, type 2a and type 2b. Type 1 fibres use oxygen to produce energy and contract slowly which is why they are known as slow twitch, high oxidative fibres. They are ideally suited for long, slow work. Type 2a fibres predominantly use oxygen to produce energy but do have some capacity to produce energy anaerobically. They are known as fast twitch, high oxidative fibres and are ideally suited to moderate intensity work of medium duration. Type 2b fibres rely on anaerobic metabolism to produce energy and are the fastest contracting fibre type, hence they are known as fast twitch, low oxidative fibres and are ideally suited for sprint work.
Different breeds of horses are born with different percentages of the 3 types of muscle fibres. Draught horses have more type I fibres than Thoroughbreds. Quarter horses have the highest percentage of type 2b fibres. This explains why some breeds are better suited to certain sports than others. Endurance sports require slow twitch fibres that are resistant to fatigue whereas sports involving sprinting need a higher proportion of fast contracting fibres which unfortunately happen to readily fatigue. Arab horses in particular appear to be genetically adapted to endurance exercise more than any other breed. Research suggests that not only do they possess a more economical gait, they also have a greater oxidative capacity due to the increased numbers of type 1 muscle fibres.
Training does not change the twitch type (slow or fast) but there is some adaptability between type 2a and type 2b fibres. Over a 6 month period the ratio of 2a:2b fibres increases which favours aerobic metabolism of fat and has a sparing effect on the muscle stores of glycogen. By sparing muscle glycogen, muscular endurance is enhanced and fatigue is delayed.
Fatigue is the likely cause of your horse losing its oomph
Muscular fatigue is not just tiredness it is a decrease in the ability to perform work. You can see this manifested in the racehorse slowing during the final stages of a race, the show jumper unable to jump as high, the eventer failing to clear the last fence or the endurance horse unable to maintain their pace. Fatigue occurs primarily due to the depletion of energy stores or the build-up of lactic acid. Energy production (and as a result exercise) in the horse is almost never limited by the body’s stores of fat. However, low to moderate intensity exercise when sustained over a long period of time can lead to glycogen depletion. The type 1 muscle fibres which are recruited first in this type of exercise are also the first to fatigue through glycogen depletion. As they become fatigued type 2a fibres are recruited and, if exercise continues, are the next to deplete their stores of glycogen and become fatigued. Finally, if exercise continues for long enough Type 2b fibres are recruited and fatigued. The muscles are then entirely dependent on the fat stores for energy which significantly reduces the rate of metabolism forcing the horse to slow down.
Sources of energy
The main sources of energy in the diet are carbohydrates, fats and fibre which are broken down into glucose and fatty acids to be used as fuel either through aerobic or anaerobic metabolism. Protein is commonly overfed to horses and is only used as an energy source if there is a lack of carbohydrates or fats. Carbohydrates (starch and sugar) are the major contributor of glucose with cereal grains (oats, corn, barley and wheat) containing a relatively large amount of starch compared with forages. A performance horse’s diet can only contain so much starch. If large amounts of starch are fed in a single meal the small intestine becomes overwhelmed and is unable to digest all of it. Undigested starch then flows to the large intestine where it is fermented and produces lactic acid which can lead to colic and laminitis. Fibre is supplied in large amounts by forage but can also come from chaff, alfalfa meal, beep pulp and soya hulls. The latter two are fermentable fibres and are sometimes referred to as “super fibres” as they typically have higher energy values that traditional forage.
Fats, unsurprisingly, supply fatty acids and are a useful source of energy for performance horses. They contain 2.5 times the energy per weight of carbohydrates and can be used to boost the calorific content of the ration without increasing the meal size. Researchers found that horses fed additional fat daily for 5-12 weeks showed improved glycogen sparing capability, an important consideration since glycogen depletion can cause the oomph to go out of your horse. Vegetable oils such as rice bran and seeds such as linseed or sunflower are good sources of supplementary fat. Ideally choose an oil high in Omega 3 fatty acids and low in Omega 6 fatty acids. Omega 3 fatty acids have an anti-inflammatory action and have been shown to reduce inflammation in cells from horse joints as well as help horses prone to skin conditions like sweet itch.
So the answer to the question, what can I feed my horse for more oomph, requires a three pronged approach:
Take another look at your fitness training – the fitter your horse the better its body gets at transporting oxygen to the muscles and using it there to produce energy thereby delaying the onset of fatigue. It also results in greater glycogen storage capacity in the muscle meaning that glycogen depletion and the resulting fatigue is again reduced or delayed.
Accept that if your horse is more draught than thoroughbred then fitness training is even more important to encourage adaptability of muscle fibres to favour aerobic metabolism of fat for energy and therefore sparing the stores of glycogen in the muscle.
Carbohydrates, fat and fibre are the main fuel for work. Increasing the amount of fat, in the form of vegetable or seed oils, can help protect against the effects of glycogen depletion.
One final thought, the way you ride can have an impact on whether the horse uses the aerobic or anaerobic pathway to generate energy. A rider who changes pace quickly coming into a jump and then kicks on hard when going away from the fence demands a greater anaerobic contribution from their horse than a rider who maintains a steady rhythm around the whole course.