Getting the best possible performance from an equine athlete requires not just excellent fitness and training (as well as rider skills!) but also excellent feeding and nutrition to fuel the work effort. This article will review some of the key nutrients required for exercise, as well as some feeding guidelines for competition.
Fuel for Movement
Repeated muscular contraction, as required during exercise, is fueled by adenosine triphosphate (ATP). ATP is produced in the body by a series of metabolic reactions from energetic substrates such as carbohydrates (mostly blood glucose or muscle glycogen, the storage form of glucose in the body) and fats (in the blood from diet or with breakdown of adipose tissue/fat reserves, or fat stored within the muscle).
ATP production is dependent both on the fuel type, and how quickly ATP needs to be produced – which is based on the intensity of the exercise. At all times both fat and carbohydrates will be used, but the proportions will change. At the start of exercise, some ATP is stored in the muscle, while ATP can also be replenished rapidly through the creatine phosphate system. These reserves only last a few seconds, after which anaerobic metabolism kicks in.
Muscle glycogen (primarily) can be broken down quickly without oxygen to produce ATP and lactic acid. This type of energy production occurs with high intensity bouts of exercise, such as during a jump-off. The build-up of lactic acid is a potential consequence and can cause fatigue during these types of events.
During longer-duration, lower-intensity exercise such as endurance rides, dressage tests, and hunter rounds, the respiratory rate increases and oxygen is available for aerobic metabolism. This type of energy production can use both carbohydrates (from muscle glycogen and glucose from the blood) and fats, although fat metabolism will produce far more ATP than carbohydrate metabolism. Fat metabolism does require a small amount of carbohydrate availability, and during long bouts of exercise, such as 100-km endurance rides, carbohydrate (glycogen) availability becomes limiting and the horse can fatigue as it runs out of this fuel.
Diet can be influential on these reserves, and to some degree which fuel is used. For example, some research has suggested that feeding horses high fat diets can shift fuel preference from glycogen metabolism to fat metabolism, thus “sparing” glycogen stores, and potentially decreasing lactic acid production during higher-intensity exercise.
Digestible Energy for Calories
Regardless of what fuel is used to produce ATP, we still need to get that fuel into the body. Dietary digestible energy (DE) requirements are measured in calories, and in megacalories (Mcal) for the horse. Horses in work need increasingly more calories in their diets to sustain workloads (see Table 1 on pg 24), such that horses in heavy work need almost twice as many calories per day as when they are idle.
These “digestible energy” requirements are based on the amount of energy that is actually available for the horse after digestion of a feed. Different feeds have different digestibilities based on their chemical nature and the horse’s digestive tract’s ability to break these down.
For example, fats have very high amounts of DE because they can produce lots of ATP when metabolized and they are well digested by the horse (Table 2).
Cereal grains, such as corn or oats, have quite a bit of starch in them (about 70% starch in corn and 50% in oats) which is digested to glucose relatively easily in the horse, and thus provide moderate amounts of DE.
Forages (hay, pasture), because they contain more indigestible fibre, have lower digestibility, and therefore have lower amounts of DE. This is why when feeding performance horses we tend to feed more “concentrated” sources of energy (cereal grains, commercial grain mixes, fats) and lower amounts of forages. This is also because a high-intensity working horse couldn’t eat enough forage to meet its energy requirements, simply because space in the digestive tract is limited.
Protein for Muscle
Athletic horses also have a higher requirement for protein, measured as crude protein (CP), to help support muscle turnover. As well, some protein and nitrogen, the key element found in protein, is lost in sweat, particularly “latharin,” the foamy type of sweat.
However, protein itself is a poor energy source and is not directly used for metabolic production of ATP. If the horse is fed more protein than it needs for muscle synthesis, etc., protein can be metabolized into compounds that can enter into the various metabolic pathways to produce ATP. This is a rather inefficient process, however, and the nitrogen component of sweat needs to be removed and converted to urea for excretion in urine, which requires water. Therefore, as noted in Table 1, increases in protein requirements do not increase to the same magnitude as energy requirements do. Further, feeding too much protein has resulted in negative outcomes in some research studies, including increased ammonia in the blood, altered pH, and some measures of reduced performance.
Vitamin and Minerals
Mineral and vitamin requirements will also increase with exercise, notably calcium (Ca) and phosphorus (P) requirements, the key components of bone remodeling. These requirements are typically met when feed intake is increased, but may be limiting if a horse is fed cereal grains (notably low in Ca, see Table 2). Also remember than Ca and P should always be provided in approximately a 2:1 ratio.
The electrolytes sodium (Na), potassium (K), and chloride (Cl) are lost in sweat and need to be replaced in the diet, particularly when a horse is working hard, and/or in a hot environment. All exercising horses should be offered a free-choice salt source and an electrolyte supplement during hot weather, and even during the cooler season when working. (Perhaps a given, but horses should also have fresh, clean water available at all times.)
It should be noted that many commercial electrolyte supplements do not actually provide enough salt. Some only contain a few grams, while a horse could need upwards of 100 grams, and some contain too much sugar. Some sugar can actually help electrolyte absorption from the digestive tract, but too much isn’t good. It is easy and cheap to make a homemade mix by combining equal parts (25-100 grams total depending on the workload) of regular table salt (NaCl) and “lite” salt (KCl), and adding a teaspoon of sugar.
Vitamin E requirements increase with exercise, as they are a key anti-oxidant that can, along with selenium, protect against the oxidative products that are produced with exercise. Vitamin C and beta-carotene (a precursor for vitamin A) are also anti-oxidants and may have higher requirements during exercise. Some of the B vitamins have important actions in metabolic pathways that produce energy, but these are synthesized by the microbes in the horse’s digestive tract and are not thought to be limiting.
Minerals and vitamins will be fortified in a commercial feed that is designed for athletic horses, so additional supplementation is not warranted. Some research has shown that elite athletic horses are over-supplemented, which can cause toxicity or inhibition of other nutrient availability.
Feed Management at Shows
Horses are ‘trickle’ feeders and their digestive tract is designed to digest fibre such as forages, which are the most important component of a horse’s diet other than water. They can provide the majority of the nutrients required by the horse and fill their digestive tract with ample fibre to keep it healthy and ward off colic and gastric ulcers. Good-quality hay can also satisfy the horse’s natural grazing behaviour and help avoid the development of stereotypies such as cribbing, stall walking, and wood chewing.
It is extremely important for competitors to not overlook their hay sources as they travel to shows. Always insist to see a hay analysis upon purchase; this way, you can ensure your concentrated feeds are sufficient in providing whatever nutrients the hay may lack.
Competitors should also be mindful of switching to new forage sources at each venue, and should attempt to slowly adapt horses to all new feeds, both hay and concentrates, to help avoid colic. To avoid too much hay sitting in the belly during competition, it is generally recommended that hay be removed a few hours before competition.
Commercial concentrates formulated for athletic horses are ideal because they are formulated with the added nutrients such horses need. Some horses are sensitive to dietary sugar and starch (often referred to as non-structural carbohydrates, or NSC), which may make them temporarily “hot” after feeding (like a kid after eating a chocolate bar). Selecting lower NSC feeds, or avoiding feeding too soon prior to riding, can help alleviate these issues. However, athletic horses need starch and sugar to get glucose, which is required for glycogen synthesis, so don’t go too overboard by limiting NSC and feeding too much fat.
It is generally a good practice to feed a horse 4-6 hours prior to competition, so that fuel reserves are “topped up” prior to exercise. Feeding causes fluid shifts and hormone release that might be counter-productive to exercise, which is why feeding large amounts of feed (notably sugars and starches) prior to exercise is not recommended.
In lower-intensity exercise, or over long durations (such as hanging out at the hunter ring), it may be a good idea to offer small amounts of hay and concentrates between rounds. Likewise, offering small amounts of concentrates to show jumpers between the first round and the jump-off might help them “top up” again for that last round.
One small research study reported that glucose concentrations were significantly (and scarily) low at the end of a jump-off. Repeated work efforts over several days, such as expected of eventers or jumpers during a week at Spruce Meadows, requires critical feeding to ensure horses are topped up safely between days and events.
In my experience, many top competitors overlook nutrition. It is not enough to simply buy the venue-provided hay and feed a grain-mix recommended by a salesperson, offer a few supplements and expect a million-dollar horse (or any horse) to perform at its best. Owners should work with an equine nutritionist to help them examine their horse’s diet and formulate a feeding plan to optimize health and performance.