Focus article: Carbohydrates in the diet of the performance horse
Carbohydrates & Starch An exercising horse involved in short duration - high intensity exercise may benefit from carbohydrate based energy sources. As a follow up on our article related to “Energy substrates and energy utilization pathways” we will focus in this article in more detail on the use of highly available carbohydrate sources in short duration – high intensity exercise (e.g. race horses performing in a 2 - 3 minute time frame). An important fuel used to provide energy to these horses are glucose and glycogen (both glucose and glycogen are forms of glycogen). Cereals like oats, wheat, barley, maize and spelt are common suppliers of starch in the horse diet. Some cereals may also have a so called 'heating' effect on (some) horses. The effect may vary between horses and diets. It does not mean the horse took in more energy or more heat is generated in the hindgut but the horses get more excitable. Oats, wheat and spelt are generally known to have this “heating” effect.
The starch digestibility in the small intestine may differ between different starch sources. In general, the digestibility of oat starch exceeds that of corn starch or barley starch before reaching the hindgut. The starch digestibility of cereals in the small intestine can be increased by improving the accessibility of the starch to enzyme degradation. The granular structure of the starch can be destroyed mechanically or by heat and pressure in combination with moisture. Thermal processing results in irreversible swelling and destruction of the internal structure of the starch granules (e.g. gelatinization). Consequently, an increase in the availability of starch for enzymatic digestion might alter the blood glucose (and in sulin) response, as more substrate will be absorbed in the small intestine. The magnitude and time of the glucose response varies between carbohydrates sources. Barley, maize and roughage will show lower peaks and occur later whilst rolled oats, wheat flakes and dextrose will result in higher peaks that occur faster.
Thus, both grain source and processing influence carbohydrate digestion and consequently the glucose response towards a meal. Thus, the digestion and absorption of grain meals affects the use of substrates used during exercise.
Pre- and post race carbohydrate considerations for horses performing short duration - high intensity exercise
Feeding for performance is the combination of combining sound scientific principles and empirical knowledge as science has not yet elucidated the "ideal" ration for a performance horse. At the start of a race a horse should be fully hydrated with optimal amounts of liver and muscle glycogen that after appropriate training and conditioning is primed for efficient energy use.
Some Pre-race feeding suggestions related to carbohydrate feeding:
• Feed a balanced ration (A somewhat higher fat content of the diet may be of value but the horse should be adapted to such diet for about 2 months; however carbohydrates are the main energy source for this type of exercise. The horse should not loose weight during the training process and should be fed according to its energy requirement.
• Glycogen loading; feeding a carbohydrate-rich diet as of 3 days prior to the contest (divided over multiple meals!). More information regarding glycogen loading can be found here. N.B. "Excess" Glucose (energy) that is not stored in the body as glycogen will be deposited as fat.
• One should be careful feeding (large) grain or starchy meals within less than 2-3 hours before competition. Horses lacking fitness during competition may benefit from feeding 1 kg of processed grains (preferably rolled oats and wheat flakes) not less than 1- 2 hours prior to competition. Cavalor Superforce may be fed at 1 - 1,5h (max) pre-race/competition. Note: feed timing is very important here.
Post race feeding carbohydrate suggestions
• Horses may benefit from the feeding of a small dose (100 gr) of quickly digestible sugars (dextrose) within 45 minutes after the contest or race in combination with the Amino Acids... (For Anabolic Effect).
• Feeding a ration containing easily available carbohydrates (high glaecemic index) has been shown to hasten muscle glycogen synthesis. Careful feeding management should be ensured to minimize health risks associated with a high soluble carbohydrate intake. Electrolyte supplementation may have an additional benefit upon compensating for electrolyte losses as it helps muscle glycogen resynthesis during the recovery period.
There has been a considerable amount of study investigating carbohydrate supplementation with respect to reducing glycogen depletion during exercise and promoting glycogen repletion after exercise. However, the impact on immune function has not been addressed in horses. In humans, the size of the glycogen and liver stores at the onset of exercise has also been shown to influence the hormonal and immune response to exercise. Current knowledge points that the immunomodulating effect of carbohydrate supplementation may be of interest of horses participating in endurance-type activities.
Considerations when feeding high carbohydrate diets to horses
• The horse capacity to digest high amounts grains into starch and sugars is limited. The horse has a short small intestine and a limited quantity of enzymes (amylase) to digest cereal derived starch when compared to other species. An excess of starch that is not or insufficiently processed may result in a flow of undigested starch in the hindgut, increasing lactic acid production in the hind gut. This may increase the risk for colic. Horses should be fed multiple meals per day and the starch content of a meal should be less than < 2,5 g starch / kg horse / meal.
• Feeding high grain rations to growing horses on a daily basis has been pointed out as a potential cause of Osteochondrosis Disseccans (OCD). High blood glucose levels and insulin may interfere with the development of cartilage into mature bone. Therefore, it is not recommended to feed carbohydrate sources to young growing horses that result in high glucose or insulin responses (e.g. feedstuffs with a high glycaemic index). Young growing horses may be fed feedstuffs that are known to elicit a moderate or low glycaemic and insulinaemic response. These horses may benefit more from a higher percentage of oil and fibre and oil based rations.
• In horses, glucose and insulin control maybe impaired in a number of conditions and/or life stages such as diabetes, obesity, gestation, pituituiry dysfunction, laminitis and or aging. Using easily available carbohydrate (high glycaemic index) in horses in rations for these horses is contraindicated. When the horse is sensitive to tying-up or muscle problems (related to glycogen-storage) a oil & fibre based ration should be considered.
The amount and type of carbohydrates that may be included in the horse ration depends on the total ration and may vary between horses and the type of exercise and condition (age, physical condition, temper, etc) and circumstances the horse is being kept. For example, a 500 kg stabled horse with limited pasture access will not need more than 1 kg of oats and a horse given one hour of light exercise daily may need up to 1.5 kg. A horse that is intensively trained may receive about 2.5 kg. Similar to other nutrients in the diet, the correct amounts and type of carbohydrate supplementation should be discussed with the eye on the individual needs of the horse and the type of exercise the horse has to perform.