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Fueling the Performance Horse

Updated: Mar 23, 2023

What you’re feeding the performance horse will act as fuel for their muscles, and just like how some of us only go to certain gas stations, careful consideration of the fill up step is important! To understand why, we must consider how muscles turn fuel into the energy that gets harnessed for athletic pursuits.

Muscle Fiber Recruitment & Energy Substrates

Muscle is made up of different types of fibers, which are recruited for different uses based on type of exercise and intensity (McKenzie, 2011b).

Three main muscle fiber types:

  • Type 1: Slow Twitch - prefers fat as a substrate

  • Type 2a: Fast Twitch (oxidative) - can use fats or carbs as a substrates

  • Type 2x: Fast Twitch (glycolytic) - can only use carbs as a substrate

Muscle fibers use different energy substrates for fuel. Type 1 & Type 2a use fatty acids in the presence of oxygen to produce ATP to fuel continuous exercise, and thus are oxidative/aerobic form of energy metabolism, while Type 2x uses muscle glycogen to fuel short bursts of intense movement, and thus is a glycolytic/anaerobic form of energy metabolism (Lawrence, 2008; McKenzie, 2011b).

  • Oxidative/aerobic metabolism favour use of fatty acids, and is more fatigue resistant as they do not alter intracellular pH.

  • Glycolytic/anaerobic metabolism used for full intensity/force generation, and uses glycogen to produce ATP to fuel this intense muscle contraction. However, the metabolism of these substrates also produces lactic acid, and excessive lactic acid production will drop muscle pH and impair contraction, leading to fatigue.

Fitness work increases Type 2a: Type 2x muscle fiber type ratios, glycogen storage, and utilization of energy substrates.The fit horse will have slower utilization of muscle glycogen and blood glucose, and a greater reliance on fat oxidation. As oxidative muscle fibers are more fatigue resistant, this leads to better performance and more endurance. Interval training can help improve muscle fiber adaptations to exercise without the risk of injury associated with high speed training (McKenzie, 2011b).

Muscle fiber proportions also vary by breed - quarter horses have a higher proportion of Type 2x fibers as they are purpose bred for short-bursts of speed, while thoroughbreds have higher proportions of Type 2a fibers, as they are purpose-bred for speed and endurance over longer endurances (McKenzie 2011b). Thoroughbreds can also have a higher proportion of their body mass made up of muscle mass (55%), compared to other breeds (~45%) - these are some reasons why Thoroughbred blood is considered so important in eventing, particularly the cross country phase.

Muscle Fiber Recruitment

Type 1 fibers are found more in deep tissue and major type found in postural muscles, while Type 2 are found more superficially, and the largest proportion of type 2 fibers are found in the gluteal muscles, for propulsion. This reflects the pattern of muscle fiber recruitment, as deep muscle tissues (Type 1) are required for movement, and then Type 2 are recruited as physical effort increases (McKenzie, 2011b).

These fibers also differ based on the muscle contraction speed, which impacts how they are used. Muscle fiber recruitment starts with mostly Type 1 fibers, as these are the lowest threshold and easy to activate, as well as some Type 2a. These fibers function very efficiently when oxygen is present, and can use both fats or glycogen. As exercise persists, or becomes more intense and surpasses the anaerobic threshold, fast twitch-glycolytic fibers are used. Brunner et al (2012, 2014) found that horses competing in the jumping phases of FEI level eventing and showjumping both commonly exceed anaerobic threshold, and that some eventing horses have also been found to pass this threshold in the dressage phase as well.

Type 2x fibers are only recruited near maximal intensity or after long durations of submaximal exercise. These fibers fatigue quickly, as they produce lactic acid along with ATP, which overtime, drops the muscle pH and inhibits muscle contraction. Fatigue can also be caused by glycogen depletion, altered electrolyte concentrations and high muscle temperatures.

Types of Energy Substrates (and sources in the diet)

Fatty acids

  • Horses can get energy from fiber from roughage due to a symbiotic relationship with microbes in their hindgut. While mammals cannot break down plant cell wall components, as we lack the enzymes required to do so, the microbes within the hindgut can. As such, roughage is fermented in the cecum to produce short-chain fatty acids (SCFA) such as acetate, propionate and butyrate, which are available to the horse for energy.

  • Fatty acids are also available from fat in the diet, indirectly from fiber fermentation products (SCFA), and from fat reserves in the body (ie, breaking down triglycerides, FFA, etc).

Glycogen (stored glucose)

  • Grain is digested in the small intestine to produce starch, which is transformed to glucose and transported in the blood.

  • Propionate, a SCFA, can also be transformed into glucose in the liver.The stored form of glucose is called glycogen, and is stored in the muscle and in the liver (Lawrence, 2008).

Fueling Up: Feeding Energy Substrates DOs & DON’Ts

If you have a performance horse who seems to get tired at competitions, it could be that they’re literally out of fuel. Fitness work is key to maximizing endurance, as maximizing Type 2a recruitment, oxidation efficiency AND use of fatty acids as fuel by supplying adequate fuel can help delay switching into the muscle glycogen stores & the consequent lactic acid production.

Glycogen repletion takes 48-72 hours (Waller et al, 2009), with 96 hours reported depending on severity of exercise - a major concern for horses who are performing exercise bouts back to back (ie, multi-segment or multi-day show). While soluble carbohydrate provision works to increase glycogen repletion in humans, it shows little benefit for the horse. Post-exercise feeding can help glycogen synthesis and repletion, but does not have to be carb-based - you can also provide energy substrates which spare glucose-use, so that glucose can instead be used for glycogen synthesis (Goer and Harris, 2014).

DON’T: Carb Loading

Pre-exercise carbohydrate loading does not work in the horse - in fact, it can cause your horse to fatigue earlier! Insulin peaks following a grain meal restrains fat oxidation, so the horse has to use glycogen stores as an energy source right off the bat, instead of saving those stores for explosive bursts. As such, fatigue and exhaustion will occur earlier in exercise if it is done after concentrate feeding (Brunner et al, 2014; Lawrence et al, 1993).

DON’T: Rely solely on grain.

Traditionally, it’s been thought that what type of exercise your horse is performing will determine what their diet is made up of - high fiber and fat diets for horses who do long duration work and high starch diets for horses in speed events. However, modern equine nutrition research has noted that this is not the case. There are concerns about whether grain is necessary for glycogen repletion. While some horses may benefit from some grain in the diet (Mesquitra et al, 2014), both forage-only and low-starch, high-fat diets have been reported to be an alternative to feeding high-grain diets to race horses, and have noted no differences in performance (Connysson, Muhonen and Jansson, 2017; Finno et al, 2010). Forage- and fiber-based diets may also increase aerobic energy utilization and lactate threshold, increasing time to fatigue (Jansson and Lindberg, 2012). Careful selection of quality fibers can drive major energy contributions in the diet, minimizing risk of gastric upset, tying up and ulcer development.

DO: Optimize Hydration

Interestly, horses on a roughage-rich diet have also shown greater capacity for gluconeogenesis than horses on a starch rich diet, and fueled gluconeogenesis with SCFA propionate (Frape, 1998). As Waller et al (2009) found that horses supplemented with electrolytes had 3 times faster glycogen repletion than unsupplemented horses, it’s likely that glycogen repletion is connected to hydration status. Fiber has high water-holding properties in the gut (Walker and Collins, 2017) and may improve the water reservoir in the GI tract, thus better maintaining water required to produce glycogen. Glycogen is stored within a 1:3 ratio with water (Waller et al, 2009), so it’s possible that dietary strategies which optimize hydration should optimize recovery! Selection and proper provision of an electrolyte supplement is critical in supporting hydration status of performance horses.

DO: Consider fat sources.

Fat is an energetically dense ingredient, and offers more than double the amount of digestible energy than grains. In addition, fat in the diet of exercising horses has been found to have a glycogen-sparing effect in some studies, while reducing tying up in race horses, and contributing to calmer behavior (Finno et al, 2010; Lacombe, Hinchcliff and Taylor, 2003). As such, it can be a useful alternative energy source, especially for horses who cannot tolerate high-starch feeds.

DO: Maximize Forage

While hay quality & selection is key for forage-only diets, and some horses may benefit from additional energy sources, it’s important that we don’t underestimate the nutritive value that fiber has for horses. While this might look a little different for every horse, depending on how much hay they will voluntarily consume and the hay available, maximizing forage in your horse’s diet is an incredibly valuable nutrition strategy when considering whole-animal health optimization!

Follow along for more educational equine nutrition content, or get in touch for help fueling your equine athlete!



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