Metabolic Management of your Endurance Athlete

Notes from a lecture presented by Dr. Susan Garlinghouse at the ECTRA Winter Getaway 2017

For horses covering long distances, the management of metabolic health is of the highest priority.  For the competitive distance rider, attention paid to these specific parameters can spell the difference between a completion and a pull (or retirement, for riders used to other disciplines). Distance riding is a sport whose mantra is the phrase, “to finish is to win”.  Most distance riders want to have a fun and successful weekend, which means that they are bringing home a healthy horse; to this end, they are always working to learn how to better care for their mounts.

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Dr. Susan Garlinghouse (photo from AERC)

Dr. Susan Garlinghouse presented “Beating the Metabolic Pull” at the Eastern Competitive Trail Ride Association (ECTRA) Winter Getaway in Boxborough, MA in early February, offering attendees instruction and strategies based on the most current of scientific evidence.

Dr. Garlinghouse is an endurance rider and has completed the grueling Tevis Cup no less than three times.  She has ridden her Tennessee Walking Horse John Henry over 2,800 endurance miles.  Garlinghouse referenced John Henry many times during her talks throughout the weekend, as her insights into metabolic management have been influenced by the additional challenge posed by preparing a horse with a dense build for strenuous competition.  She is a well-known authority on many of the unique health and maintenance issues faced by the distance horse.

Garlinghouse emphasized that during a ride there are three primary factors which must be managed to ensure the horse’s wellbeing:  hydration, gut motility and energy balance.  They are listed here in their relative order of importance, and we will explore each one now in a little more detail.

Hydration

Garlinghouse says that 90% of metabolic issues come from hydration loss.  The line between “sufficient hydration” and a horse at risk is incredibly narrow.  Horses sweat at the rate of 1.5-3.75 gallons per hour, and may produce over forty gallons of sweat during a 50 mile ride.  During heavy exercise, horses may lose 5-6% of their body weight, with about 4-5 gallons of net fluid loss.

Dehydration during heavy work can affect equine athletes in all disciplines, and the effects come on quickly, beginning with 2-3% dehydration rates.   Health concerns escalate rapidly from there.  At 6% dehydration, capillary refill time and heart rate are elevated.  At 8%, capillary refill time will be 2-3 seconds (normal is under 1), with dry mucous membranes, dry or mucous covered feces, and decreased urine output.  At 10% dehydration, capillary refill time will be over three seconds, and the horse will have a high, hanging heart rate with weakness and cold extremities; this horse is in serious trouble.  At 12%, the horse is close to death.

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The difference between 4 to 8% hydration in a 1000 pound horse is only 4-5 gallons of water.

Some riders believe that the horse will naturally consume water sufficient to replace this lost fluid, but this is a myth.  According to research done on fluid balance in endurance horses conducted at UC Davis, the horse will only replace about 2/3 of fluid loss through voluntary drinking.  For example, if ten gallons of fluid have been lost, the horse will only voluntarily consume 6-7 gallons.  Equally concerning is that this same research showed that over 60% of the horses starting at the 100 mile endurance rides where the studies were being conducted were already dehydrated to some extent, prior to starting the ride.  Another 20% were at the high end of normal.  Just 10% of the starters began the ride at optimal hydration.

Therefore, it becomes incumbent to create situations in which the horse will stay at a higher rate of hydration before and during the ride.

Garlinghouse offered several strategies to help with this.  Even for the non-distance rider, some of these practices could help enhance their performance horse’s well-being, especially before intense work or competition.  First, Garlinghouse recommends feeding lots and lots of hay—horses will drink 1.5-2 gallons of water for every five pounds of hay that they consume. She also reminded the audience that the rate of passage from the mouth to the hind gut is relatively slow. What you feed your horse on Thursday becomes their source of energy on Saturday.

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Roughage should always be at least 50% of your horse’s ration, and for a distance horse, more is better.

Feeding soluble fibers, like beet pulp or soybean hulls, can also increase the fluid reservoir available to the horse during a ride.  These feed stuffs help to retain fluid and electrolytes which the horse can pull from during exertion.

The manner in which we feed our horses is also important to consider.  Garlinghouse explained that there are fluid shifts in the body associated with the consumption of large (over 4.5 pounds), episodic (fed more than 2-3 hours apart) meals.  When we feed on this schedule, as much as 5-6 gallons of fluid shifts from the plasma and tissues and into the gastrointestinal tract, leading to a 15-24% reduction in plasma volume.  The effect is transient, lasting two to three hours.

If your horse is at rest, this isn’t a big deal.  But if your horse is teetering on the edge of being dehydrated, and then there is this huge fluid shift…well, that is not good.

To prevent this, riders must ensure that their horse has something going into their digestive system more frequently than every two hours.  Garlinghouse emphasized that the quantity doesn’t have to be great—grazing, some carrots or apples, a baggie of soaked beet pulp—will all do just fine.

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Soaked beet pulp.  Photo credit:  www.equinenutritionnerd.com

On a related note, Garlinghouse cautioned riders about the common practice of syringing large doses of electrolytes into the horse’s mouth, as this draws fluids from the plasma and into the digestive tract in a similar way to large servings of food.  The effect can be minimized or eliminated by giving electrolytes in small but frequent doses, preferably after the horse has been drinking.  So eight, 2 ounce doses is preferable to two, 8 ounce doses.  Garlinghouse also recommends mixing electrolytes with a buffer like kaolin pectin to help reduce the risk of ulcers.

Another cause of excess dehydration is feeding high amounts of protein.  Garlinghouse recommends feeding distance horses at a 10% protein rate.  Protein fed at higher rates will be used for energy production, but processing protein in this manner results in waste heat, almost 3-6 times as much as what is produced through the processing of fats or carbohydrates.

Garlinghouse’s “Fast Facts” on Hydration:

  • Maximize your horse’s forage intake for 2-3 days before the big ride to increase their reservoir of fluids and electrolytes
  • Provide small, frequent meals throughout the ride rather than a few large ones
  • Minimize the amount of protein in the diet

Gut Motility

While dehydration is responsible for 90% of metabolic problems, gut motility can be one of the first accurate indicators of stress.  Gut motility slows down when blood supply is reduced, which can happen anytime the horse’s systems are under excessive demand somewhere else.  This is because the gastrointestinal system is the last in line in terms of the “pecking order” amongst the horse’s body systems; vital organs like the brain, heart and lungs come first, followed by the muscles of locomotion, then skin surfaces for heat dissipation…and then the GI tract.  This chain of command stems from the horse’s prey animal status; if you are about to be eaten, it is more important that you can effectively run away than that you can digest your breakfast.

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Equine digestive system.  Photo credit: http://www.threeoaksequine.com

For the well-being of the horse, it is important to actively monitor and stimulate GI activity during a ride.  Garlinghouse recommends carrying a high quality stethoscope and have a vet teach the rider how to check all four quadrants.  Improving motility can be as simple as keeping small amounts of feed in the stomach, which triggers a hormonal release thereby increasing motility.  Another strategy is to occasionally slow down, which will reduce heat production and therefore the demand on the skin surfaces to release excess heat.   The nature of distance riding can cause a horse’s body to think is constantly being chased.  Slowing down will reverse this effect.

Garlinghouse cautions against feeding pellets or cubes at a ride, both of which require extra fluids to process.  Instead, feed soaked products, including hay.  The better the horse’s overall hydration, the more efficiently he will circulate his blood and therefore improve his gut motility.

Energy Balance

A distant third to hydration and gut motility in terms of managing the horse’s metabolism during a ride is energy balance.  There are many different strategies related to effectively managing a horse’s feed ration leading up to and during a ride.  Garlinghouse helped to dispel some common misconceptions and offered some practical tips to help ensure adequate energy reserves for the endurance horse.

There are two primary sources of energy for exercise:  fats and glucose (from carbohydrates).  Fats are more energy dense, offering 2.25 times the energy of an equivalent amount of carbohydrate, and the body can store fats in much greater quantities.  Glucose is generated from the breakdown of carbs; limited amounts are stored as glycogen in the muscle and liver, but glucose is the limiting substrate in fatigue.  Therefore, the thoughtful rider should be trying to maintain glycogen stores by balancing the diet with fat.

Garlinghouse suggests a ration with 10-12% fat in a commercial grain is acceptable, so long as horses are given time to get used to it.  Fats are calorically dense and help to maintain the horse’s body weight.  They also have a glycogen sparing effect.  Additionally, Garlinghouse recommends supplementing with a glucose source throughout the ride.  Riders should not provide extra fats during a ride, as the horse cannot process fat that quickly.  A horse in good body condition already has all the fat they need for the day’s energy requirements.  Horses should not arrive at the ride so thin that ribs are visible, as they do not have an adequate fat reserve.

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My distance horse, Lee, has been running on ProForce Fuel for the past three seasons.  It is 12% protein/13% fat.

One of Garlinghouse’s most important messages related to energy balance was that horses should not receive a large grain meal within four hours of their ride.  Feeding grain causes an increase in blood pressure, triggers insulin release and inhibits the utilization of fat.   In the distance athlete, this is particularly troublesome because the horse will experience something similar to a ‘sugar high’; the transient effects of the grain meal will cause the horse to be hyper to start the ride but then they will experience a ‘crash’.  Most grain digestion occurs in the small intestine, and the stresses of the ride will cause some of the grain to spill into the cecum undigested.  The bacteria which live in the cecum are not able to process grain, and this can cause GI stress.

Garlinghouse again emphasized that horses should be fed a meal with a high glycogen index (like a sloppy beet pulp meal) not later than midnight before a ride.  On the ride morning, horses should receive unlimited hay and then small, frequent meals throughout the ride day, which will minimize the insulin response while maintaining gut motility.

Final Thoughts

There is certainly always more to learn when it comes to managing a horse’s well being during a long distance ride.   Garlinghouse gave attendees plenty to think about and apply to their own horse’s feeding and management strategies as we move into the 2017 season.

 

 

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