Recharge Your Horse's Batteries
- Jun 1, 2002
For horses engaged in regular conditioning and competition, an important consideration for overall health and fitness is the speed of recovery following hard workouts and competition exercise. A bout of exercise burns body fuel, results in loss of water and electrolytes, and strains supporting structures such as bones, tendons, and ligaments. It stands to reason, then, that the horse must be provided adequate opportunity to restore fuel, water, and electrolyte reserves and repair any tissue damage--in other words, enough time to "recharge the batteries." Failure to do so might result in poor exercise performance, and over time signs of overtraining such as poor appetite, loss of body weight, or a lack of drive/enthusiasm during training might appear.
In this article, we will consider the physiology of post-exercise recovery with a view to the length of time needed for the batteries to recharge. We will also discuss strategies for optimizing the recovery process.
What Do We Mean by Recovery?
In the context of exercise, recovery implies that the body has recuperated from the prior period of exertion. Recovery can be classified as partial or complete. The partial recovery scenario is used during interval training, in which the horse is given a short rest, often until some target heart rate is achieved, before the next hard effort is started1. The goal is to provide maximum training stimulus without overstraining body systems.
Complete recovery implies a complete recuperation such that the horse is fresh and ready to go again. Some of the key questions are:
- What constitutes a full recovery?
- What is the time period required for full recovery? and
- What strategies can be used to speed recovery, or at least ensure that a complete recovery occurs before the next hard exercise event?
The shorter the interval between hard bouts of exercise, the more critical it is that recovery be completed in as short a time as possible. The three-day event horse is a perfect example--the cross-country day is very taxing, and yet the horse needs to be sufficiently recuperated to pass veterinary inspection the following morning and be ready to undertake stadium jumping. Muscle fatigue and other carryover effects from cross-country can impair performance during the jumping event and make the difference between winning and losing.
Western events such as reining, barrel racing, and pole bending are other situations where quick recovery is imperative.
For some competitive disciplines the horse's short-term recovery response has important implications for continuing in the event. Again, three-day eventing comes to mind, as does endurance racing.
So, we can view post-exercise recovery in two lights. First is the very short-term (30 minutes or so) phase of recuperation following completion of an exercise bout. Second, there is a longer phase of recovery, perhaps as long as one or two days depending on the intensity and duration of the exercise effort.
Factors Affecting Recovery Rate
Many factors influence the rate of recovery, and horse owners should have some appreciation of the impact of the most important elements. These include the horse's fitness level, the intensity and duration of the exercise, the environmental conditions, and whether or not specific strategies to speed recovery are used. The need for travel right after a competition can also delay recovery by limiting the opportunity for refueling. (Long road trips, by their very nature, are tiring.)
First, let's review the changes in body function demanded by physical exertion and their implications for recovery. The horse's metabolism is cranked up several notches during exercise--as much as 35-40 fold relative to rest with hard galloping, with smaller increases seen during slower work (e.g., a six- to eight-fold increase in metabolic rate during a steady trot). This upstroke in metabolic rate means an increase in the rate of use of stored body fuel--a bit like stepping on the accelerator in your car or truck. Because the conversion of stored energy into kinetic energy (energy associated with motion) is inefficient, there is an accumulation of heat in muscle with a resultant increase in body temperature.
The two major fuels used for exercise are glucose and fatty acids (both are required for hard exercise). Glucose is stored as glycogen in the liver and in skeletal muscle, while fatty acids are stored in muscle and in fat (adipose) tissue throughout the body. Fat stores in the body are virtually unlimited with respect to fuel for exercise. On the other hand, the body's store of glucose (carbohydrate) is much more limited and exercise performance will suffer when glycogen stores become low. Therefore, a major focus of recovery is the replenishment of muscle glycogen. More on this later.
When you "step on" the accelerator and ask your horse to work, his rate of glycogen use markedly increases. Thus, moderate canter and galloping exercise can significantly deplete glycogen stores. Similarly, hill, interval, and jumping work can empty the glycogen tank. On the other hand, light exercise for an hour or so (e.g., a combination of walk, trot, and light canter) will not greatly tax the body's glucose stores because a considerable amount of fat can be utilized during these lighter forms of exercise.
So, one of the keys in developing training and competition schedules is to avoid back-to-back hard efforts that might get to the "bottom" of the horse's fuel reserves. At least two days of light exercise between hard efforts is recommended.
The duration and intensity of exercise also dictate the extent of the rise in body temperature and the quantity of sweat and electrolyte losses. The other important factor is the weather. During one hour of light work in cool conditions (less than 65-70°F or 18-21°C), body temperature might increase by only 1-2°F. On the other hand, three to five minutes of a hard canter or gallop, or an interval session, could result in a 3-4°F increase in body temperature (measured with a rectal thermometer).
When the ambient (environmental) temperature rises (particularly above 80°F or 26.6°C), the efficiency of heat loss decreases and the rise in body temperature will be greater for any amount of exercise--often dictating the need for aggressive cooling procedures after exercise to hasten recovery. This is especially true when the relative humidity is also high (because high humidity decreases the ability to evaporate sweat for cooling).
Sweat fluid losses will also vary with the work effort and ambient conditions. An average-size horse (1,100 pounds or 495 kg) might lose approximately two gallons (six to eight liters) of sweat during one hour of exercise in cool conditions, but this figure could double in hot weather; i.e., up to almost four gallons per hour (15 liters).
These figures give you an idea of the volume of water your horse will need to consume in order to replace his exercise-induced sweat losses. In addition, you can estimate electrolyte losses. Each gallon of sweat will contain up to one ounce (30 grams) of salt and smaller amounts of potassium, magnesium, and calcium.
Studies of high-level performance horses (such as endurance horses, three-day eventers, and racehorses) have indicated that "race day" body weight loss of 30-60 pounds (13.5-27 kg) is common. Much of this loss is water and will be replaced when the horse consumes water during the post-exercise period. However, in some cases, a smaller (10-20 pound or 4.5-9.5 kg) weight deficit persists for two to three days. Some of this might be a reduction in gut fill, in part because of a decrease in feed intake on competition day.
What to Look For
You should always evaluate and monitor your horse's vital signs (i.e., heart rate, respiration rate, and body temperature) during the post-exercise period, particularly after strenuous or prolonged workouts in the summer months when heat stress is always a concern. Keep records of normal resting heart rate, respiration rate, and rectal temperature and compare these numbers to those recorded during the post-exercise period. When truly at rest (and not distracted), the resting heart rate of most horses is somewhere between 30-40 beats/minute, respiration rate is between 12-20 breaths/minute, and rectal temperature should be 99-100°F (37.2-37.7°C).
Heart rate decreases rapidly during the first minute after the cessation of exercise, with a more gradual decline over the subsequent 15 or so minutes. In most fit horses, heart rate is less than 50 beats per minute (or even near resting values) within 15 minutes of the completion of exercise. The post-exercise decrease in heart rate is somewhat slower in overly hot, dehydrated horses, although respiration rate and rectal temperature will give you the best indication of heat stress.
Still, there is always cause for concern if the horse's heart rate recovery is substantially delayed (e.g., the heart rate remains above 70 beats/minute at 30 minutes post-exercise). Heat stress is a possibility in these situations; hydration status and body temperature should be closely monitored and active cooling, some form of fluid replacement, and veterinary attention might be necessary. Persistent elevations in heart rate might indicate illness or injury, and should be investigated further.
Even in cool conditions, the horse's respiratory rate will be elevated for 30 minutes to an hour after hard exercise--perhaps 60-80 breaths per minute for the first 10 minutes of recovery. Hot horses will have much higher breathing rates--as high as 120 or more breaths per minute, which reflects use of the respiratory system for heat loss. However, you should be concerned when the respiratory rate remains this high after five to 10 minutes of rest--this is an indication that your horse is overheated and in need of active cooling.
You should measure the horse's rectal temperature after hard workouts. A rectal temperature in excess of 105-106°F (40.6-41.1°C) indicates the need for aggressive cooling. In most situations, respiration and rectal temperature should be at resting levels one hour after exercise.
After the cool-out period, closely inspect the legs and palpate the joints and tendons to check for injuries (e.g., interference cuts and tendon swelling). The early application of cold therapy (e.g., cool-water hosing or cold wraps), and/or a little physiotherapy (physical therapy), is very important for a speedy recovery from these problems.
Assessing the adequacy of fluid and energy replacement is more difficult. In an ideal world, every farm and stable would have a horse scale, thus allowing the routine measurement of body weight. For horses in regular training, day-to-day body weight will indicate the adequacy of rehydration after exercise and, looking at data over a period of weeks and months, body weight points toward the adequacy (or not) of energy in the diet; not enough groceries and body weight decreases (and vice versa).
Most of you will need to use a body condition score (BCS) as a guide to "energy balance," targeting a moderate BCS of around 5 for most athletic endeavors. Bear in mind that a one-unit change in BCS is equivalent to 40-50 pounds (18-22.5 kg) of body weight in an 1,100-1,200-pound (495-550-kg) horse.
Post-exercise management will depend on the nature of the workout (e.g., light workout vs. competition) and the season. In general, focus on two phases--the cool-down period and the subsequent 12-24 hours. After strenuous workouts, some type of "active" cool down (e.g., five to 10 minutes of trotting and 10-15 minutes of walking) is recommended as this will speed the clearance of lactate (a metabolic waste product) from muscle and blood, and perhaps help prevent or minimize any muscle soreness.
However, common sense should prevail when the weather is hot. Shorten the cool-down and use active cooling procedures--repeated application and removal of cool water from the entire body surface when the weather is warm and the horse is overheated (i.e., his rectal temperature is above 105°F or 40.6°C)2.
The next task is rehydration. Traditionally, horse owners have not allowed "hot" horses to drink because of a perceived risk for development of colic and cold-water founder (laminitis). However, with the possible exception of very hard galloping exercise (e.g., Thoroughbred racing), it is safe for horses to drink right after exercise. In fact, clinical experience has shown that thirst drive decreases with time after exercise. Offer water as soon as is practical and let the horse drink up to two or three gallons during the initial 15 minutes of recovery.
Electrolyte replacement will also help with the rehydration process. You have several options. On an ongoing basis, provide a salt block and some loose salt (in a bucket) in the horse's stall. However, particularly during the summer months when sweat losses are higher, it is also a good idea to add up to one ounce of salt (or a commercial electrolyte supplement) to the horse's ration, including the first post-exercise meal.
The rate-limiting component of full post-exercise recovery is replenishing muscle glycogen stores. This process seems to be quite slow in horses, taking as much as 48 hours for a complete return to "resting" levels. Research in other species indicates that early post-exercise feeding is needed for optimal glycogen replenishment, and it makes sense for us to apply these same principles to horses.
Remember that glucose is needed for glycogen synthesis (not fat). This glucose will come from starch and sugars in the diet, so a typical sweet feed with cereal grains (the major source of starch) and some molasses is a good choice. After a hard, glycogen-depleting workout, offer small amounts (two to three pounds) of a grain concentrate ration as soon as 45 minutes after exercise along with good-quality forage. A second grain-concentrate meal can be given two to three hours later. An alternative is to feed a commercially available "carbo loader" product. These contain readily digestible sugars that can be used for glycogen synthesis.
Various forms of physical therapy (e.g., massage) are now widely used in the daily management of athletic horses, and these methods are probably helpful in speeding the recovery from hard exercise and easing aches and pains. Finally, letting the horse "be a horse" is important for keeping him fresh and willing during the course of training and competition. Some pasture turnout time should be part of your post-exercise recovery plan.
1 Geor, R. Priming Equine Energy Systems. The Horse, March 2002, 79-84. Article Quick Find #3358 at www.TheHorse.com.
2 Geor, R. Chilling Out After Exercise. The Horse, July 2001, 89-94. Article Quick Find #897 at www.TheHorse.com.
Geor, R. How Does Your Horse Score? The Horse, November 2001, 93-98. Article Quick Find #2861 at www.TheHorse.com.
Geor, R. Fluids And Electrolytes. The Horse, April 2000, 87-94. Article Quick Find #214 at www.TheHorse.com.
About the Author
Ray Geor, BVSc, PhD, Dipl. ACVIM, is professor and chairperson of Large Animal Clinical Sciences at the College of Veterinary Medicine at Michigan State University
POLL: Laminitis Experience