PROTEIN FOR HORSES : EQUINE ATHLETES NEED FOR PROTEIN
During hard training or competitive events, equine athletes damage muscle tissue as a result of the production of high levels of lactic acid and /or over exertion. These muscle tissues must be repaired rapidly in order to maintain improvement, ready your athlete for the next event, and alleviate stiff and sore muscles. While in hard training or before and after serious competition dietary programs must be chosen with care in order to maintain improvement, prepare his or her system for the coming event and impact quick recovery from that event. Diets chosen for your athlete must contain protein that is profiled properly ( amino acids) along will minerals, vitamins, fat and carbohydrates. High quality protein is essential for maximum performance of any equine athlete because of its amino acid profile and the availability of these amino acids. The interaction of these amino acids with vitamins and minerals are necessary interactions for improved muscle growth and repair, stronger supportive tissues, an improved carbohydrate metabolism, stronger bones and joints, thicker hoof walls and greater overall soundness.
PROTEIN
Protein can be defined as any substance which is made of amino acids in a peptide linkage. The word protein comes from the Greek word PROTOS or FIRST because protein is the basic constituent of all living cells. Protos may also be the root of the name proteus , a mythological figure who could change form. Food protein also changes form to become a body substance after being eaten. Protein makes up three - fourths of the dry weight of most living cells. Proteins are also involved in the biochemical structure of hormones, enzymes, nutrient carriers, antibodies and many other substances and functions essential to life.
AMINO ACIDS
Protein is a collection of amino acids tied together. Once the protein is consumed and digested the amino acids breakdown into single amino acids or in some cases , peptides, which are just a few amino acids tied together. Some amino acids are considered ESSENTIAL and some are considered NON ESSENTIAL. We often do not realize how much the horse needs amino acids, because we are not aware of how busy the equine system is. Every second the bone marrow makes millions of red blood cells - every four days most of the lining of the gastrointestinal tract and the blood Platelet are replaced. - Most of the white blood cells are replaced in ten days and the number of muscle cells replaced or created in horses that are training hard or performing can be staggering.
ESSENTIAL AMINO ACIDS
Essential amino acids are amino acids that cannot be synthesized by the system from other things such as vitamins or carbohydrates. These essential amino acids must be eaten every day. If not, consumed daily the horse will then borrow them from other parts of his system to provide them for his daily maintenance. Essential amino acids are extremely important to your horse. The exclusion of even one essential amino acid from the diet or the reduction of an essential amino acid in relation to its need will reduce the total protein synthesis in the system. In horses where everyday maintenance is necessary and improvement with training is required, the creation of new cells is your priority. The horse requires a precise amino acid profile. Amino acids are not just randomly joined together, but are assembled according to a detailed predetermined procedure whose sequencing is controlled by the D.N.A. In order for new cells to be synthesized, all of the amino acids in the D.N.A. profile must be available in adequate amounts. If just one amino acid in the profile is missing the creation of new cells stops. This is called first limiting amino acid.
SOURCES OF PROTEIN AND AMINO ACIDS
Horses receive protein from both their grain mix and the hay they receive. Alfalfa hay of course is very high in protein and grass hays are lower. Common sense would tell us that if you are feeding alfalfa hay, your grain mix should be lower in total protein. If you are feeding grass hay you should be feeding a grain mix that is higher in protein. Grain mixes come in all types, but in general they are a combination of pellets ,oats and corn. Corn and oats both contain protein but are low in the essential amino acid lysine. The pellets in your feed should contain additional protein sources. These sources could be and more then likely are plant protein products such as soy bean meal in combination with other of numerous processed grain by-products. Soybeans as well as processed grain by products must go through some sort of heat process. This heat can destroy some of the most important essential amino acids for the horse.. All amino acids have a different melting point. Cystine is destroyed at 175 degrees F . Lysine , which is a extremely important amino acid is destroyed at 224 degrees F.Proline is lost at 220 degrees F. Soy bean meal processors are never supposed to exceed 200 degrees F but when push comes to shove, you know what happens. Products like distillers grain or dried solubles are almost always heated at a very high temperature. This heat process destroys many valuable amino acids and makes the feed compound unbalanced to the horse causing him to not get the full value of his protein and also taxes his system excreting all those out of balance amino acids.
AMINO ACIDS AS AN ENERGY SOURCE
The horse can convert amino acids into energy. This pathway is not the most efficient method to obtain energy, but the system has many checks and balances. Amino acids that can be converted into sugars are called glycogenic. Amino acids that can be converted to fat are called ketogenic. A few amino acids can do both.( isoleucine - lysine - tyrosine ).
MAKING DECISIONS
Whether your horse is a champion racehorse or a backyard pony, the amount and quality of the protein you feed will affect him or her one way or another. Protein in general should never be fed in excess to any horse. Too much protein or protein with the wrong amino acid profile will tax the system of your horse and cause him or her to be less than he should be. This information should help you make good decisions for your horse so he or she can be all you hoped for. If you have been depending on your feed company to make all the right decisions for you -think again!.
Protein is a collection of amino acids. Every protein source is a different combination of amino acid types. Some of these combinations are very good and some are not so good. The horse’s system needs amino acids that match his needs. Total protein of your horse feed is a worthless term, unless you know the amino acid profile. Your feed tag might say 14% CRUDE PROTEIN but to the horse it might only be 8 or 9% usable protein. The more unusable protein the horse consumes the more he has to excrete. This over feeding of unusable protein stresses the horse`s system. Excess protein can contribute to higher heart and respiratory rates, higher rates of sweating and dehydration. Some studies have concluded that performance horses do not need additional protein for good performance. These studies however do not take in to account the quality of the protein and how it might contribute to the gradual weakening of supportive tissue, bone loss, muscle atrophy and the weakening of blood vessel walls that eventually lead to bleeding or breakdown.
To produce new cells the horse`s D.N.A. has a recipe for every different kind of cell in the horse. When you feed your horse, the protein he consumes is broken down into individual amino acids. The blood stream carries these amino acids to the site they are needed, much like a conveyer belt. Lets imagine that each new cell the horse needs that day is a cake. Millions of D.N.A. cooks are standing along the conveyer belt waiting for the raw materials to bake that cake. As the raw materials pass by the cooks start grabbing all the components of their cake. When all the materials have reached that cook he grabs a little energy to bake the cake and “ walla” a new cake or cell has been created. If for some reason in four hours the cook is still missing one ingredient, he must put every component he has gathered up until that point back on the conveyer belt and start all over again. If the cook is short just one ingredient or can find no energy to bake the cake, no new cake or cell can be created.
THE HORSES NEED FOR AMINO ACIDS
LYSINE - An essential amino acid & high percentage constituent of muscle. Usually the most limiting amino acid in grain diets. Precursor for acetyl coa ( a critical nutrient for carbohydrate metabolism ). Large percentage constituent of collagen. Precursor for carnitine. Normal metabolism requires RIBOFLAVIN-NIACIN - B6 - IRON.
METHIONINE - An important essential amino acid constituent of muscle. Possible link in endochondral ossification. Regulates cell metabolism & growth. Low methionine creates folic acid deficiencies. Normal metabolism requires B12 - FOLIC ACID - B6 - MAGNESIUM.
PHENYLALANINE - An essential amino acid constituent of muscle. Precursor for catecholamine - which are adrenalin like substances. - Can be an effective pain killer and may enhance acupuncture. Normal metabolism requires - IRON - B6 - & COPPER. Precursor for tyrosine.
CYSTEINE - Precursor for cystine, necessary component of glutathione & the production of mucopolysaccharides (joint fluids ). Maintains integrity of red blood cells and is involved in the production of red blood cell membrane. Important in energy metabolism. Has the ability to clear out lungs. As cystine, component of muscle & hormones. Protects against per oxidation & is a detoxifying agent. Normal metabolism requires MAGNESIUM & ZINC.
ARGININE - An important constituent of muscle. Precursor for high energy compounds such as CREATINE. Primary in the removal of the waste products of muscle work (urea cycle ). Precursor of PROLINE (main component of collagen ) Collagen is the supportive tissue of skin, tendons, cartilage & connective tissue.
GLYCINE - Required in high levels for optimum growth & healing. Required for the production of D.N.A. Raises blood sugar levels. normal metabolism requires COPPER & CHOLINE.
TYROSINE - A constituent of muscle. Precursor for dopamine, norepinephrine, & epinephrine ( adrenalin ). Stress increases requirement. Normal metabolism requires FOLIC ACID & COPPER.
TRYPTOPHAN - A low level but essential constituent of muscle. Regulates growth hormone. precursor for serotonin ( platelet clotting factor ). Pain killer- controls hypertension & anxiety. Raises blood sugar & increases zinc absorption. Normal metabolism requires - B6 & MAGNESIUM.
LEUCINE - An essential amino acid & high percentage constituent of muscle. Major metabolic regulator. Reduces muscle breakdown. Stimulates insulin release. Normal metabolism requires THIAMIN - RIBOFLAVIN - BIOTIN & COPPER.
CARNITINE - Speeds usage of fats. increases adenosine triphosphate levels -ATP Aids conversion of amino acids to fuel within the muscle. Improves stress & exercise tolerance.
HISTIDINE - An essential amino acid constituent of muscle. Aids copper transport within the system. Reduces the effects of arthritis. Precursor for histamine - an important neurotransmitter. Normal metabolism requires COPPER - ZINC & VITAMIN E.
TYROSINE - A constituent of muscle. Precursor for dopamine, norepinephrine, & epinephrine ( adrenalin ). Stress increases requirement. Normal metabolism requires FOLIC ACID & COPPER.
Friday, December 29, 2000
Wednesday, December 20, 2000
Ride Manager`s Checklist - Mickie Newman
(To help poor frazzled ride managers to remember what they need to explain at ride meetings!)
This list encompasses both Endurance, LD and CTR. You may need to adapt some of these itemso to your own organiztion`s rules.
# Thank everyone for coming.
# Give ride time (for competitive), start time(s) and whether or not there will be a wake- up call. policy for start (endurance and LD, shotgun or controlled; competitive, what intervals and if you are letting groups go as we have been doing).
# Introduce vets and any other judges, and have them give parameters and any other info they feel is needed.
# Policy for disposal of manure. some places want it piled, some scattered, some picked up. riders need to know what policy is for that location. also policy for trash, whether there are dumpsters ( and what to do if they are full) or if it`s pack-in- pack-out.
# If a rider decides to pull for any reason, please notify someone in management so that they are not sending out a search party.
# On competitive rides, there are NO PIT CREWS allowed. you may have someone hold your horse for you but that is it. no sponging, no walking, no saddling, etc. the committee realizes that carrying a muck tub alone is not feasible, so you may have someone help with that (riders frequently double up on this duty to help each other out) but not do it for you. juniors may have their tack checked by adults to ensure safety but still need to be responsible for their own mounts. also, on competitive rides there is no forward motion allowed while off the horse (you may get off to rest but must not progress. some rides/ vets require forward motion for the last mile or two; if so notify the riders of this.
# Trail: markings, signs, landmarks (especially what to look for if there is vandalism), hazards.
# Location of P/R areas and any special problems, regulations etc.
# Ask if there are any new riders and invite them to stay after for further explanations.
# Explain emergency proceedures. point out horse ambulance and remind people to make sure its path out stays clear. if 911 works in your area remind people that if they need to call their home phone will appear to the dispatcher so it`s especially necessary to be as specific as possible with your location.
# Encourage people to fill out their surveys, whether AHAO members or not. these are very helpful to management, giving them ideas on things to keep or improve in future years. NOVICES (in AHAO rules "novice" is first or 2nd year horse or rider; so this is more for a "newbie" clasification)
# Ask how many first-time riders are present and encourage them again to please ask questions if there`s anything you don`t cover or that they don`t understand.
# Explain the process for pulse checks, coming into set hold for competitive or gate-into-a-hold for LD. explain that each rider has the right to ask for an immediate recheck but that the second one counts.
# If you will be using monitors at any checks explain that AHAO rules state we may use either monitors or stethoscopes as long as it`s the same for everyone at a check. rechecks will be done by stethoscope.
# Rules state that riders have "any reasonable time" for completion. reasonable is determined by the ride management. this clause is in the rules to allow for extra time taken due to vandalism, weather setbacks, or other problems that may legitimately arise. we do not want you to hurt your horse, but we also do not want you to be having a picnic and have all of the staff waiting on you (this is CTR only; endurance has times set by AERC).
# For LD rides, make sure the riders know that finish is determined by when the horse pulses down to 60 (which must be done within 30 minutes of arrival), NOT by being first across the line. remind new riders of the signs of overriding and what to watch out for. if they are unfamiliar with taking pulses, explain the procedure and encourage them to try it. Even if they do not own a stethoscope, most experienced riders, pit crews or P/R staff (providing they are not occupied with duties at the time) are usually glad to give a demo. Explain (or have the vet do so) what metabolic parameters are looked at and why.
# Ride staff are volunteers. if there are any problems we of course do not want you to hesitate to bring them to our attention. but please remember that these people are doing this for very little compensation (usually just food and a completion award). be nice to them!
This list encompasses both Endurance, LD and CTR. You may need to adapt some of these itemso to your own organiztion`s rules.
# Thank everyone for coming.
# Give ride time (for competitive), start time(s) and whether or not there will be a wake- up call. policy for start (endurance and LD, shotgun or controlled; competitive, what intervals and if you are letting groups go as we have been doing).
# Introduce vets and any other judges, and have them give parameters and any other info they feel is needed.
# Policy for disposal of manure. some places want it piled, some scattered, some picked up. riders need to know what policy is for that location. also policy for trash, whether there are dumpsters ( and what to do if they are full) or if it`s pack-in- pack-out.
# If a rider decides to pull for any reason, please notify someone in management so that they are not sending out a search party.
# On competitive rides, there are NO PIT CREWS allowed. you may have someone hold your horse for you but that is it. no sponging, no walking, no saddling, etc. the committee realizes that carrying a muck tub alone is not feasible, so you may have someone help with that (riders frequently double up on this duty to help each other out) but not do it for you. juniors may have their tack checked by adults to ensure safety but still need to be responsible for their own mounts. also, on competitive rides there is no forward motion allowed while off the horse (you may get off to rest but must not progress. some rides/ vets require forward motion for the last mile or two; if so notify the riders of this.
# Trail: markings, signs, landmarks (especially what to look for if there is vandalism), hazards.
# Location of P/R areas and any special problems, regulations etc.
# Ask if there are any new riders and invite them to stay after for further explanations.
# Explain emergency proceedures. point out horse ambulance and remind people to make sure its path out stays clear. if 911 works in your area remind people that if they need to call their home phone will appear to the dispatcher so it`s especially necessary to be as specific as possible with your location.
# Encourage people to fill out their surveys, whether AHAO members or not. these are very helpful to management, giving them ideas on things to keep or improve in future years. NOVICES (in AHAO rules "novice" is first or 2nd year horse or rider; so this is more for a "newbie" clasification)
# Ask how many first-time riders are present and encourage them again to please ask questions if there`s anything you don`t cover or that they don`t understand.
# Explain the process for pulse checks, coming into set hold for competitive or gate-into-a-hold for LD. explain that each rider has the right to ask for an immediate recheck but that the second one counts.
# If you will be using monitors at any checks explain that AHAO rules state we may use either monitors or stethoscopes as long as it`s the same for everyone at a check. rechecks will be done by stethoscope.
# Rules state that riders have "any reasonable time" for completion. reasonable is determined by the ride management. this clause is in the rules to allow for extra time taken due to vandalism, weather setbacks, or other problems that may legitimately arise. we do not want you to hurt your horse, but we also do not want you to be having a picnic and have all of the staff waiting on you (this is CTR only; endurance has times set by AERC).
# For LD rides, make sure the riders know that finish is determined by when the horse pulses down to 60 (which must be done within 30 minutes of arrival), NOT by being first across the line. remind new riders of the signs of overriding and what to watch out for. if they are unfamiliar with taking pulses, explain the procedure and encourage them to try it. Even if they do not own a stethoscope, most experienced riders, pit crews or P/R staff (providing they are not occupied with duties at the time) are usually glad to give a demo. Explain (or have the vet do so) what metabolic parameters are looked at and why.
# Ride staff are volunteers. if there are any problems we of course do not want you to hesitate to bring them to our attention. but please remember that these people are doing this for very little compensation (usually just food and a completion award). be nice to them!
Tying Up - Exertional rhabdomyolysis - Susan Garlinghouse
contributed by Susan Garlinghouse
Exertional rhabdomyolysis -excruciatingly specific details of what`s happening at the cellular level.
The complete pathophysiology (Why It Happens) of exertional rhabdomyolysis (most commonly called "tying up") is still not completely understood. Currently, the conditions that are known to be factors in causing tying up are
# resting a conditioned horse on a full-grain diet, followed by exercise ("Monday morning disease");
# whole-body potassium depletion;
# selenium deficiency; an unaccustomed level of exercise;
# postviral infections, particularly rhino;
# intoxications with ionophores (a substance which increases cellular permeability to a specific ion, which would in turn disrupt the electrical potential of the cell), blister beetle, mercury, coffee bean (cassia) or gossypol from raw cottonseed.
Other factors which have been suggested as being contributory are hypothyroidism, some high-performance lines of horses, nervous horses, fillies, shock, laminitis, tetanus, neural injury, estrus, hyperestrogenism (resulting from possibly a granulosa cell tumor), cold damp weather, heavy muscling, and low-sodium rations. Electrolyte depletion, especially calcium, magnesium and chloride may also cause muscle cramps, which are sometimes referred to as slow-onset rhabdomyolysis; or synchronous diaphragmatic flutter, commonly called "thumps". These are related syndromes, but not exactly the same as the syndrome described here, which is most accurately described as acute rhabdomyolysis.
One of the current hypotheses is that when a conditioned horse is not worked and kept on full feed high in soluble carbohydrates (such as grain), the horse will accumulate carbohydrates in the muscles. If there is a sudden demand for work, the body cannot adequately remove the rapidly accumulating lactic acid in the muscles. This in turn causes vasospasms and ischemia---which means essentially that the surrounding blood vessels "clamp down" so that the lactic acid waste product cannot be removed. As a result, intracellular pH drops, the muscle cell is disrupted and you get the hard, crampy muscles you see when a horse ties up.
Other theories of the biochemical mechanism is that there is a deficiency of the high-energy phosphates in muscle cells following maximal, anaerobic exertion, and/or a depletion of muscle glycogen after prolonged, slow (endurance-type) exercise. High body temperatures and electrolyte imbalances/depletions are also probably contributing causes, and certainly major factors in endurance horses that tie up during competitions.
Unless you`re a biochemist, all of these different theories essentially boil down to the same net effect---the ion pumps (ie, sodium/potassium, calcium/magnesium and calcium/ATPase) in the membrane surrounding the muscle cell which move substrates in and out of the cell are disrupted, and so the interior environment of the muscle cells either cannot get rid of waste products of metabolism, OR has too much of a metabolic substrate to be able to function, OR can`t get enough of a metabolic substrate to be able to function. And so the muscle cell simply shuts down. When muscle cells shut down, they don`t do so in the relaxed position, they freeze up in the contracted position, which is why you get those rock-hard muscles. Biochemically, it`s not all that different from rigor mortis.
The effect on kidneys comes in when the connective tissue (the sarcolemma) surrounding and enclosing the muscle cell is disrupted, releasing the contents of the muscle cell into the bloodstream. There are lots of different proteins and substrates and whatnot in a muscle cell, but the important one for this particular discussion is myoglobin. Myoglobin is a protein pigment which is responsible for oxygen transport in the muscle cell. Hemoglobin transports oxygen in the bloodstream, myoglobin transports oxygen in the muscle cell. When myoglobin is released from a disrupted muscle cell into the bloodstream, it travels to the kidneys and is filtered out. In being filtered out of the bloodstream (and keep in mind, there`s probably a lot of it from the kidney`s point of view), it causes (or CAN cause) kidney damage or even total renal failure by overwhelming and clogging up the kidney tubules and restricting the blood (and therefore oxygen) supply to the kidney tissue. This effect will be worsened if the animal is hypovolemic, meaning he`s dehydrated and therefore has a decreased total plasma volume. A decreased plasma volume means that in turn the blood is thicker and that the heart must work harder to circulate. And this in turn means that less oxygen to delivered to the muscles and organs, fewer substrates, less waste product removed, and so on. A vicious cycle sort of thing.
So while myoglobin does not directly damage the kidneys, in great enough concentration it will cause damage indirectly by clogging them up and creating what is called myoglobinuric nephrosis and possibly renal failure. It`s also the myoglobin being filtered out that shows up as very dark urine. The dark urine itself is not what you have to worry about---what you DO have to worry about is the fact that myoglobin in the urine means that significant muscle disruption and damage has occurred in the system, and that the kidneys are being overwhelmed with a whole lot of waste product to try and get rid of. Needless to say, this is serious s**t from the physiological point of view. However, dark urine doesn`t always mean myoglobinuria. Dark urine can be caused by other things as well. But if your horse is dehydrated, won`t move and is standing there hunched up and miserable and the urine looks a lot like coffee---you`ve got problems.
Some of the other things a veterinarian will look for in a suspected tying-up horse are elevated enzymes in the blood plasma, specifically CK (creatinine kinase) and AST (aspartate aminotransferase). AST is also referred to as SGOT, but both refer to the same enzyme. There are other things the vet will look for as well, like creatinine, urea, electrolytes and so on, but enzyme levels are at the top of the list. CK and AST are both enzymes contained in the muscle cell (as well as other types of cells) which are released into the blood when the muscle cell is disrupted. Therefore, if the enzyme levels are elevated in the blood panel, it must mean that tissue cells somewhere are being (or were being) damaged. The tricky part in diagnosis is figuring out where tissue damage is occurring---AST occurs in both muscle and liver cells, so elevated levels could mean problems in either muscle OR liver (and for that matter, AST levels can also be elevated by certain drugs or toxins). CK levels will indicate muscle damage, while other elevated enzymes in the blood panel will indicate liver damage. And to make things even more confusing, there are various isoforms of yet another enzyme, LDH (lactate dehydrogenase) which will indicate whether muscle damage occurring is from skeletal or cardiac (heart) muscle.
The elevation in CK will be detectable within a few hours of the onset of clinical symptoms, peak within 24 hours and decline fairly quickly. CK`s half-life is six hours, meaning that half of the amount remaining is removed within six hours. Hence, 50% is gone within 6 hours, 75% is gone within 12 hrs, 87.5% is gone within 18 hrs, 93.75% is removed within 24 hrs, and so on. The concept of "half-lifes" doesn`t refer only to enzymes, by the way, the same general idea applies to drug half-lifes, isotope half-life, etc etc (just a little extra trivia for you)(I know, riveting.)
The rise in levels of AST will peak approximately 24 hours after the onset of the clinical signs of tying up, and decline much more slowly---AST has a half-life of about 14 days, so with significant muscle damage, it`ll be awhile before levels are really back to normal. The relative levels of these two enzymes, among other things, are what a DVM will look at in determining the extent of damage, whether damage is still occurring and how long ago the initial damage occurred. For example, if a horse transport company delivers a horse doing a good impersonation of a piece of granite, and swears the horse must have injured himself last week before they ever laid eyes on him...but the blood analysis shows screaming CK levels (indicating recent muscle damage) and relatively low AST levels (also indicating recent damage), then the transport companies arguments can be classified under the heading of I Don`t Think So Chuckles.
References:
Hodgson, DR, Rose, RJ (1994): The Athletic Horse. W.B. Saunders, Philadelphia. pg. 169-174.
Kobluk, CN, Ames, TR, Geor, RJ (ed)(1995): The Horse, Disease and Clinical Management. W.B. Saunders, Philadelphia. pg. 809-810, 1278-1279, 1317-1318.
Lewis, LD (1995): Equine Cliinical Nutrition, Feeding and Care. Williams & Wilkins, Baltimore. pg. 262-263.
Copyright 1998 Susan Evans Garlinghouse.
Exertional rhabdomyolysis -excruciatingly specific details of what`s happening at the cellular level.
The complete pathophysiology (Why It Happens) of exertional rhabdomyolysis (most commonly called "tying up") is still not completely understood. Currently, the conditions that are known to be factors in causing tying up are
# resting a conditioned horse on a full-grain diet, followed by exercise ("Monday morning disease");
# whole-body potassium depletion;
# selenium deficiency; an unaccustomed level of exercise;
# postviral infections, particularly rhino;
# intoxications with ionophores (a substance which increases cellular permeability to a specific ion, which would in turn disrupt the electrical potential of the cell), blister beetle, mercury, coffee bean (cassia) or gossypol from raw cottonseed.
Other factors which have been suggested as being contributory are hypothyroidism, some high-performance lines of horses, nervous horses, fillies, shock, laminitis, tetanus, neural injury, estrus, hyperestrogenism (resulting from possibly a granulosa cell tumor), cold damp weather, heavy muscling, and low-sodium rations. Electrolyte depletion, especially calcium, magnesium and chloride may also cause muscle cramps, which are sometimes referred to as slow-onset rhabdomyolysis; or synchronous diaphragmatic flutter, commonly called "thumps". These are related syndromes, but not exactly the same as the syndrome described here, which is most accurately described as acute rhabdomyolysis.
One of the current hypotheses is that when a conditioned horse is not worked and kept on full feed high in soluble carbohydrates (such as grain), the horse will accumulate carbohydrates in the muscles. If there is a sudden demand for work, the body cannot adequately remove the rapidly accumulating lactic acid in the muscles. This in turn causes vasospasms and ischemia---which means essentially that the surrounding blood vessels "clamp down" so that the lactic acid waste product cannot be removed. As a result, intracellular pH drops, the muscle cell is disrupted and you get the hard, crampy muscles you see when a horse ties up.
Other theories of the biochemical mechanism is that there is a deficiency of the high-energy phosphates in muscle cells following maximal, anaerobic exertion, and/or a depletion of muscle glycogen after prolonged, slow (endurance-type) exercise. High body temperatures and electrolyte imbalances/depletions are also probably contributing causes, and certainly major factors in endurance horses that tie up during competitions.
Unless you`re a biochemist, all of these different theories essentially boil down to the same net effect---the ion pumps (ie, sodium/potassium, calcium/magnesium and calcium/ATPase) in the membrane surrounding the muscle cell which move substrates in and out of the cell are disrupted, and so the interior environment of the muscle cells either cannot get rid of waste products of metabolism, OR has too much of a metabolic substrate to be able to function, OR can`t get enough of a metabolic substrate to be able to function. And so the muscle cell simply shuts down. When muscle cells shut down, they don`t do so in the relaxed position, they freeze up in the contracted position, which is why you get those rock-hard muscles. Biochemically, it`s not all that different from rigor mortis.
The effect on kidneys comes in when the connective tissue (the sarcolemma) surrounding and enclosing the muscle cell is disrupted, releasing the contents of the muscle cell into the bloodstream. There are lots of different proteins and substrates and whatnot in a muscle cell, but the important one for this particular discussion is myoglobin. Myoglobin is a protein pigment which is responsible for oxygen transport in the muscle cell. Hemoglobin transports oxygen in the bloodstream, myoglobin transports oxygen in the muscle cell. When myoglobin is released from a disrupted muscle cell into the bloodstream, it travels to the kidneys and is filtered out. In being filtered out of the bloodstream (and keep in mind, there`s probably a lot of it from the kidney`s point of view), it causes (or CAN cause) kidney damage or even total renal failure by overwhelming and clogging up the kidney tubules and restricting the blood (and therefore oxygen) supply to the kidney tissue. This effect will be worsened if the animal is hypovolemic, meaning he`s dehydrated and therefore has a decreased total plasma volume. A decreased plasma volume means that in turn the blood is thicker and that the heart must work harder to circulate. And this in turn means that less oxygen to delivered to the muscles and organs, fewer substrates, less waste product removed, and so on. A vicious cycle sort of thing.
So while myoglobin does not directly damage the kidneys, in great enough concentration it will cause damage indirectly by clogging them up and creating what is called myoglobinuric nephrosis and possibly renal failure. It`s also the myoglobin being filtered out that shows up as very dark urine. The dark urine itself is not what you have to worry about---what you DO have to worry about is the fact that myoglobin in the urine means that significant muscle disruption and damage has occurred in the system, and that the kidneys are being overwhelmed with a whole lot of waste product to try and get rid of. Needless to say, this is serious s**t from the physiological point of view. However, dark urine doesn`t always mean myoglobinuria. Dark urine can be caused by other things as well. But if your horse is dehydrated, won`t move and is standing there hunched up and miserable and the urine looks a lot like coffee---you`ve got problems.
Some of the other things a veterinarian will look for in a suspected tying-up horse are elevated enzymes in the blood plasma, specifically CK (creatinine kinase) and AST (aspartate aminotransferase). AST is also referred to as SGOT, but both refer to the same enzyme. There are other things the vet will look for as well, like creatinine, urea, electrolytes and so on, but enzyme levels are at the top of the list. CK and AST are both enzymes contained in the muscle cell (as well as other types of cells) which are released into the blood when the muscle cell is disrupted. Therefore, if the enzyme levels are elevated in the blood panel, it must mean that tissue cells somewhere are being (or were being) damaged. The tricky part in diagnosis is figuring out where tissue damage is occurring---AST occurs in both muscle and liver cells, so elevated levels could mean problems in either muscle OR liver (and for that matter, AST levels can also be elevated by certain drugs or toxins). CK levels will indicate muscle damage, while other elevated enzymes in the blood panel will indicate liver damage. And to make things even more confusing, there are various isoforms of yet another enzyme, LDH (lactate dehydrogenase) which will indicate whether muscle damage occurring is from skeletal or cardiac (heart) muscle.
The elevation in CK will be detectable within a few hours of the onset of clinical symptoms, peak within 24 hours and decline fairly quickly. CK`s half-life is six hours, meaning that half of the amount remaining is removed within six hours. Hence, 50% is gone within 6 hours, 75% is gone within 12 hrs, 87.5% is gone within 18 hrs, 93.75% is removed within 24 hrs, and so on. The concept of "half-lifes" doesn`t refer only to enzymes, by the way, the same general idea applies to drug half-lifes, isotope half-life, etc etc (just a little extra trivia for you)(I know, riveting.)
The rise in levels of AST will peak approximately 24 hours after the onset of the clinical signs of tying up, and decline much more slowly---AST has a half-life of about 14 days, so with significant muscle damage, it`ll be awhile before levels are really back to normal. The relative levels of these two enzymes, among other things, are what a DVM will look at in determining the extent of damage, whether damage is still occurring and how long ago the initial damage occurred. For example, if a horse transport company delivers a horse doing a good impersonation of a piece of granite, and swears the horse must have injured himself last week before they ever laid eyes on him...but the blood analysis shows screaming CK levels (indicating recent muscle damage) and relatively low AST levels (also indicating recent damage), then the transport companies arguments can be classified under the heading of I Don`t Think So Chuckles.
References:
Hodgson, DR, Rose, RJ (1994): The Athletic Horse. W.B. Saunders, Philadelphia. pg. 169-174.
Kobluk, CN, Ames, TR, Geor, RJ (ed)(1995): The Horse, Disease and Clinical Management. W.B. Saunders, Philadelphia. pg. 809-810, 1278-1279, 1317-1318.
Lewis, LD (1995): Equine Cliinical Nutrition, Feeding and Care. Williams & Wilkins, Baltimore. pg. 262-263.
Copyright 1998 Susan Evans Garlinghouse.
Thursday, December 07, 2000
Electrolytes - Managing Heat Scientifically. Part I - Cooling - Abby Bloxsom
By Abby Bloxsom, courtesy of Eastern Competitive Trail Ride Association, www.ectra.org
A Little Background
No matter where you ride or what distance you ride at, no matter what your experience or how fit your horse is, heat and humidity make distance riding harder. The horse is an arctic adapted species – in a summer coat, its body is temperature-neutral between about 30 and 60 degrees Fahrenheit, meaning that it will not have to expend energy to either cool off or heat up within that temperature range. Humans are not set up that way. Our small, flat, mostly hairless bodies with blood vessels close to the surface evolved in tropical climates (until we learned to dress ourselves, at which point our territory expanded gradually over the globe). Naked, we get cold quite easily.
This means that while we prefer to ride and compete in the summer, the heat and humidity of that season places a strain on the horse’s system that we as humans may not feel. In addition to the heat of the human-preferred climate, the horse is constantly producing heat of his own. When he’s exercising, he produces it at an alarming rate. Your job as Heat Manager is to get the excess heat out of the horse’s body as quickly as possible. (On borderline coolish days – or even on a dry, breezy day when the temperature might still be fairly high – it’s also important to know when not to cool the horse. A minimum amount of heat is necessary in order to maintain the horse’s normal body temperature, but that’s a subject for another time.)
How It Works
Before I talk about how you can help your horse to keep his cool in the summer heat, I want to review a little chapter from our high school science textbooks about heat in general. There are three basic heat transfer processes: conduction, convection, and radiation. Conduction is the way that heat travels through an opaque solid, as when the handle of a frying pan gets hot during cooking (I always forget about that). The speed of transfer – the amount of heat moved over time – depends on the difference in temperature between the warmer part and the cooler part of the solid. This is called the temperature gradient.
Convection is when heat is transferred from one solid, liquid, or gas to another, such as when a warm plate on a countertop warms up the surface of the counter, or when you put your jello in the refrigerator to chill it. Again, the speed of transfer depends on the temperature gradient.
Radiation is the process involved when a material transfers heat by electromagnetic energy. This process is unique in that objects need not be in contact with each other. All objects in our everyday world radiate heat because they are warmer than absolute zero, but the amount of heat given off depends solely on the temperature of the object. A glass of lemonade in the sun will warm up because it is absorbing more radiant heat (from the sun) than it emits (by virtue of its inherent "heat").
The problem with using any one of these processes to cool the body of a horse is that – especially on a hot, sunny day – they are way too slow compared to the amount of heat that his powerful engine is producing inside his body. The horse has a large body mass, especially compared to its surface area, so the transfer of heat from the muscles (where the horse is burning fuel and creating heat) outward to the surface by conduction is inefficient. He moves a little more heat by convection, as his blood is heated and then pumped through his blood vessels to the skin. The air around a dry horse is also heated by convection, which removes heat from the horse as long as it’s cooler than the horse itself (remember the temperature gradient?) This effect is reduced to nil, however, as the ambient temperature approaches the horse’s body temperature.
The warm body of the horse also radiates heat, in increasing amounts as he heats up. Still though, if he’s standing in the sun, he’s like my glass of lemonade in that he’s soaking up a lot more infrared radiation from the sun than he’s emitting. A dark horse – like a black rubber bucket – will soak up more solar radiation than a white horse, but he also radiates more, and he’s still going to be producing many times that amount of heat by virtue of the work that he’s doing. So keep him out of the sun when you can – but you should do that with any horse anyway.
Rest assured, though, that Mother Nature has also given us a supercharger to jack up the speed at which we can transfer heat, and that is the phase change. As water changes from solid (ice) to liquid (water) to gas (water vapor), it absorbs huge amounts of thermal energy. Firefighters take advantage of this when they cool a fire by spraying a fine mist of water over it. As the water vaporizes rapidly, it sucks the heat out of the fire, cooling it instantly. The speed of evaporation is limited by the ambient relative humidity– the amount of water vapor contained in the air relative to the maximum amount of vapor that it can possibly contain at that temperature. In the case of the fire, the relative humidity is effectively zero right before the hose comes on. Because the air is superheated from the fire, the maximum amount of vapor that can be contained is very high, so the cooling potential is very high. In the bathroom after a shower, the humidity approaches 100%, so evaporation and cooling potential are very low. This cooling supercharger – evaporation – is the best tool that we have for removing heat from a hot body. That’s why we sweat.
Putting It Together
Dry Weather: In a dry climate (or even in the humid Northeastern U.S. on a dry day, say below 40 or 50% relative humidity) the sweat produced by the glands on both equine and human skin will evaporate rapidly, sucking the heat out of the skin and the blood vessels just below it. The heart can then pump this cooled blood around through the body to cool the tissues in the core of the body. The evaporative process also occurs in the passages of the horse’s airway. He breathes in dry air, and the moist tissues in the nostrils, sinuses, trachea, and lungs are cooled by evaporation (and a little bit by convection).
Remember, though, that the horse’s sweat and the moisture in his airway contain water, electrolyte salts, and some proteins that come from inside him, from the tissues of his body. You can help preserve an enormous amount of your distance horse’s vital body fluids by putting plain old water on the outside of him. That’s the first reason that we sponge. On a day that will likely be warm at the outset, it doesn’t hurt to start right out in the morning by sponging a horse before starting a ride, and preventing those early fluid losses. Continued sponging during a ride will spare even more sweat, especially if you concentrate on the areas with the most blood vessels under the skin – the chest, neck, shoulders, belly, and upper legs.
When the humidity is very low, say below 25 or 30%, evaporation can happen so fast that you might think you and the horse are not even sweating – but you are. The more water you keep on the horse’s body the less he will have to replace from the inside (a notoriously slow process). Your horse will stay cooler, his pulse will be lower, and his recovery will be faster. SO just because it’s a dry day and the horse feels fairly dry and cool, don’t stop sponging! In this type of weather, the water used for sponging can be fairly warm, since the goal is for it to evaporate (it will feel cool anyway). In fact, if the water is too cold it might actually chill the horse by removing heat too quickly. If I were competing in very dry weather (which, face it, in New England I’m not!) I’d probably refrain from clipping my horse during the competitive season. I’d want to keep the water on the horse so that it will be able to cool him by evaporation. It can’t do that if it runs off onto the ground.
Hot Weather: As the ambient temperature approaches that of the horse (100-103 degrees F), remember that the effects of conduction through the body and convection to the air are both reduced (because they depend on the temperature gradient, right?). This means first that we must rely on a new principle: convection to water. The water that goes onto the horse must be cool, so that heat will be transferred from the body to the water. As the air becomes hotter, the water needs to be cooler so that the cooling process will be faster (remember the temperature gradient). Water sponged onto the horse must be scraped off immediately (it will feel warm) and replaced with more cool water.
High air temperatures also mean that radiation and evaporation (the supercharger) become more important. It’s essential to keep the horse in the shade to minimize the heating effect of solar radiation and maximize the effect of convection to the air (cooler air means a greater difference in temperature, hence faster cooling). Standing in a breezy spot or walking the horse about slowly will increase both the evaporation and the convection rates as the air passes over the horse’s heated body. In high heat with low humidity, this may be all that’s needed.
Humid Weather: As the ambient relative humidity approaches 100% and temperatures are in the "very hot day" range, however, we have an entirely different situation. Very humid air cannot absorb water from evaporation (the steamy bathroom effect), which means that the supercharger is now out of gas. The weakling coolers of conduction, convection and radiation can do the job, but not without a lot of effort on your part. As on the hundred-degree day, you will need to get a jump on the cooling by laying on the water heavy and early.
In oppressive weather, we depend on relatively slow heat transfer processes, but they are all notorious for being painfully slow for a horse with a chunky body. A loaf of bread fresh from the oven stays warm much longer than a pancake, even a stack of pancakes, because heat has to travel much farther from the core of the bread to the outside than it does in the flat pancake. This is why my riding partner’s chunky little horse – faster and fitter than my lanky mare – inverts and has trouble recovering in muggy weather. On a cool, dry day he can trot circles around her for 25 miles!
Clipping a horse before a ride can help with cooling in humid weather – it allows the convection heating of air and water over the body to happen faster, since even the summer coat is a decent insulator. It also allows the evaporative cooling to draw more heat because it takes place closer to the blood vessels below the surface. Keeping pads, ear nets, and hanging mane to a minimum will of course also help your horse keep his cool on a muggy day.
A horse with a fast, efficient gait can sometimes manage to cool himself out on the trail by using speed to his advantage: a convection oven cooks faster by virtue of the fact that circulating the air rapidly speeds up the convection process. My husband likes a fan in the summer for the same reason. If a horse is very fit (it would be counter-productive to try this with a horse who was not up to it) moving him along the trail at a good clip (in the shade, over easy going) can speed up both convection and evaporation, even if the temperature gradient and relative humidity are not in your favor.
When the rider dismounts at a hold or the end of a ride in hot, humid weather, the saddle should be pulled immediately. Huge amounts of the coldest water need to go on the horse’s body – everywhere, but especially on those big veins of the chest, neck, head, ears, belly, and upper legs. The water must be scraped off as quickly as possible and replaced with more cold water. In effect, you’re speeding up the convection to water by circulating the water over the horse’s body. You need to keep this up as long as it takes to make the water run cool off the horse’s body.
When the water does run off cool, you’re not done. Walking the horse slowly will maintain blood circulation from the core of his body until he’s both cool and dry. You may find though, especially in a horse with a blocky body type, that he seems to heat back up again later because the body core was not as cool as the surface was. The cooling/walking cycle needs to be repeated until the horse stays cool if allowed to rest after the walk.
In An Emergency
If all else fails, and the horse really does overheat (a temperature over 103 degrees that isn’t coming down) it’s essential for the horse’s health to get the heat out as fast as possible. At this point, a horse will have been withdrawn from an ECTRA ride, so the ride rules go out the window. To take advantage of the temperature gradient, you need ice – and lots of it – in your water bucket, and you need to get the very cold water onto the entire horse as quickly as possible. Again, as long as the water comes off warmer than it went on, keep scraping it off and putting more on. Use the shade, the breeze, and walking to your advantage, and use as many people as you can get to help cool the horse before he suffers medical complications.
The Human Factor
Of course, it does no good to discuss caring for the horse if I don’t also throw in two bits about caring for the rider. On an ECTRA ride, you have no crew available to look after the horse while you go off and lie down, sponge yourself, or eat and drink. DO NOT put the horse’s welfare in front of your own at all costs, since an under-fueled or dehydrated rider can quickly become weak, disoriented, and careless. By forgetting to care for him or herself, a rider can easily jeopardize the welfare and safety of the entire team. You can use the same physics to cool your own body that you use on your horse in extreme weather conditions. Now go out and ride.
A Little Background
No matter where you ride or what distance you ride at, no matter what your experience or how fit your horse is, heat and humidity make distance riding harder. The horse is an arctic adapted species – in a summer coat, its body is temperature-neutral between about 30 and 60 degrees Fahrenheit, meaning that it will not have to expend energy to either cool off or heat up within that temperature range. Humans are not set up that way. Our small, flat, mostly hairless bodies with blood vessels close to the surface evolved in tropical climates (until we learned to dress ourselves, at which point our territory expanded gradually over the globe). Naked, we get cold quite easily.
This means that while we prefer to ride and compete in the summer, the heat and humidity of that season places a strain on the horse’s system that we as humans may not feel. In addition to the heat of the human-preferred climate, the horse is constantly producing heat of his own. When he’s exercising, he produces it at an alarming rate. Your job as Heat Manager is to get the excess heat out of the horse’s body as quickly as possible. (On borderline coolish days – or even on a dry, breezy day when the temperature might still be fairly high – it’s also important to know when not to cool the horse. A minimum amount of heat is necessary in order to maintain the horse’s normal body temperature, but that’s a subject for another time.)
How It Works
Before I talk about how you can help your horse to keep his cool in the summer heat, I want to review a little chapter from our high school science textbooks about heat in general. There are three basic heat transfer processes: conduction, convection, and radiation. Conduction is the way that heat travels through an opaque solid, as when the handle of a frying pan gets hot during cooking (I always forget about that). The speed of transfer – the amount of heat moved over time – depends on the difference in temperature between the warmer part and the cooler part of the solid. This is called the temperature gradient.
Convection is when heat is transferred from one solid, liquid, or gas to another, such as when a warm plate on a countertop warms up the surface of the counter, or when you put your jello in the refrigerator to chill it. Again, the speed of transfer depends on the temperature gradient.
Radiation is the process involved when a material transfers heat by electromagnetic energy. This process is unique in that objects need not be in contact with each other. All objects in our everyday world radiate heat because they are warmer than absolute zero, but the amount of heat given off depends solely on the temperature of the object. A glass of lemonade in the sun will warm up because it is absorbing more radiant heat (from the sun) than it emits (by virtue of its inherent "heat").
The problem with using any one of these processes to cool the body of a horse is that – especially on a hot, sunny day – they are way too slow compared to the amount of heat that his powerful engine is producing inside his body. The horse has a large body mass, especially compared to its surface area, so the transfer of heat from the muscles (where the horse is burning fuel and creating heat) outward to the surface by conduction is inefficient. He moves a little more heat by convection, as his blood is heated and then pumped through his blood vessels to the skin. The air around a dry horse is also heated by convection, which removes heat from the horse as long as it’s cooler than the horse itself (remember the temperature gradient?) This effect is reduced to nil, however, as the ambient temperature approaches the horse’s body temperature.
The warm body of the horse also radiates heat, in increasing amounts as he heats up. Still though, if he’s standing in the sun, he’s like my glass of lemonade in that he’s soaking up a lot more infrared radiation from the sun than he’s emitting. A dark horse – like a black rubber bucket – will soak up more solar radiation than a white horse, but he also radiates more, and he’s still going to be producing many times that amount of heat by virtue of the work that he’s doing. So keep him out of the sun when you can – but you should do that with any horse anyway.
Rest assured, though, that Mother Nature has also given us a supercharger to jack up the speed at which we can transfer heat, and that is the phase change. As water changes from solid (ice) to liquid (water) to gas (water vapor), it absorbs huge amounts of thermal energy. Firefighters take advantage of this when they cool a fire by spraying a fine mist of water over it. As the water vaporizes rapidly, it sucks the heat out of the fire, cooling it instantly. The speed of evaporation is limited by the ambient relative humidity– the amount of water vapor contained in the air relative to the maximum amount of vapor that it can possibly contain at that temperature. In the case of the fire, the relative humidity is effectively zero right before the hose comes on. Because the air is superheated from the fire, the maximum amount of vapor that can be contained is very high, so the cooling potential is very high. In the bathroom after a shower, the humidity approaches 100%, so evaporation and cooling potential are very low. This cooling supercharger – evaporation – is the best tool that we have for removing heat from a hot body. That’s why we sweat.
Putting It Together
Dry Weather: In a dry climate (or even in the humid Northeastern U.S. on a dry day, say below 40 or 50% relative humidity) the sweat produced by the glands on both equine and human skin will evaporate rapidly, sucking the heat out of the skin and the blood vessels just below it. The heart can then pump this cooled blood around through the body to cool the tissues in the core of the body. The evaporative process also occurs in the passages of the horse’s airway. He breathes in dry air, and the moist tissues in the nostrils, sinuses, trachea, and lungs are cooled by evaporation (and a little bit by convection).
Remember, though, that the horse’s sweat and the moisture in his airway contain water, electrolyte salts, and some proteins that come from inside him, from the tissues of his body. You can help preserve an enormous amount of your distance horse’s vital body fluids by putting plain old water on the outside of him. That’s the first reason that we sponge. On a day that will likely be warm at the outset, it doesn’t hurt to start right out in the morning by sponging a horse before starting a ride, and preventing those early fluid losses. Continued sponging during a ride will spare even more sweat, especially if you concentrate on the areas with the most blood vessels under the skin – the chest, neck, shoulders, belly, and upper legs.
When the humidity is very low, say below 25 or 30%, evaporation can happen so fast that you might think you and the horse are not even sweating – but you are. The more water you keep on the horse’s body the less he will have to replace from the inside (a notoriously slow process). Your horse will stay cooler, his pulse will be lower, and his recovery will be faster. SO just because it’s a dry day and the horse feels fairly dry and cool, don’t stop sponging! In this type of weather, the water used for sponging can be fairly warm, since the goal is for it to evaporate (it will feel cool anyway). In fact, if the water is too cold it might actually chill the horse by removing heat too quickly. If I were competing in very dry weather (which, face it, in New England I’m not!) I’d probably refrain from clipping my horse during the competitive season. I’d want to keep the water on the horse so that it will be able to cool him by evaporation. It can’t do that if it runs off onto the ground.
Hot Weather: As the ambient temperature approaches that of the horse (100-103 degrees F), remember that the effects of conduction through the body and convection to the air are both reduced (because they depend on the temperature gradient, right?). This means first that we must rely on a new principle: convection to water. The water that goes onto the horse must be cool, so that heat will be transferred from the body to the water. As the air becomes hotter, the water needs to be cooler so that the cooling process will be faster (remember the temperature gradient). Water sponged onto the horse must be scraped off immediately (it will feel warm) and replaced with more cool water.
High air temperatures also mean that radiation and evaporation (the supercharger) become more important. It’s essential to keep the horse in the shade to minimize the heating effect of solar radiation and maximize the effect of convection to the air (cooler air means a greater difference in temperature, hence faster cooling). Standing in a breezy spot or walking the horse about slowly will increase both the evaporation and the convection rates as the air passes over the horse’s heated body. In high heat with low humidity, this may be all that’s needed.
Humid Weather: As the ambient relative humidity approaches 100% and temperatures are in the "very hot day" range, however, we have an entirely different situation. Very humid air cannot absorb water from evaporation (the steamy bathroom effect), which means that the supercharger is now out of gas. The weakling coolers of conduction, convection and radiation can do the job, but not without a lot of effort on your part. As on the hundred-degree day, you will need to get a jump on the cooling by laying on the water heavy and early.
In oppressive weather, we depend on relatively slow heat transfer processes, but they are all notorious for being painfully slow for a horse with a chunky body. A loaf of bread fresh from the oven stays warm much longer than a pancake, even a stack of pancakes, because heat has to travel much farther from the core of the bread to the outside than it does in the flat pancake. This is why my riding partner’s chunky little horse – faster and fitter than my lanky mare – inverts and has trouble recovering in muggy weather. On a cool, dry day he can trot circles around her for 25 miles!
Clipping a horse before a ride can help with cooling in humid weather – it allows the convection heating of air and water over the body to happen faster, since even the summer coat is a decent insulator. It also allows the evaporative cooling to draw more heat because it takes place closer to the blood vessels below the surface. Keeping pads, ear nets, and hanging mane to a minimum will of course also help your horse keep his cool on a muggy day.
A horse with a fast, efficient gait can sometimes manage to cool himself out on the trail by using speed to his advantage: a convection oven cooks faster by virtue of the fact that circulating the air rapidly speeds up the convection process. My husband likes a fan in the summer for the same reason. If a horse is very fit (it would be counter-productive to try this with a horse who was not up to it) moving him along the trail at a good clip (in the shade, over easy going) can speed up both convection and evaporation, even if the temperature gradient and relative humidity are not in your favor.
When the rider dismounts at a hold or the end of a ride in hot, humid weather, the saddle should be pulled immediately. Huge amounts of the coldest water need to go on the horse’s body – everywhere, but especially on those big veins of the chest, neck, head, ears, belly, and upper legs. The water must be scraped off as quickly as possible and replaced with more cold water. In effect, you’re speeding up the convection to water by circulating the water over the horse’s body. You need to keep this up as long as it takes to make the water run cool off the horse’s body.
When the water does run off cool, you’re not done. Walking the horse slowly will maintain blood circulation from the core of his body until he’s both cool and dry. You may find though, especially in a horse with a blocky body type, that he seems to heat back up again later because the body core was not as cool as the surface was. The cooling/walking cycle needs to be repeated until the horse stays cool if allowed to rest after the walk.
In An Emergency
If all else fails, and the horse really does overheat (a temperature over 103 degrees that isn’t coming down) it’s essential for the horse’s health to get the heat out as fast as possible. At this point, a horse will have been withdrawn from an ECTRA ride, so the ride rules go out the window. To take advantage of the temperature gradient, you need ice – and lots of it – in your water bucket, and you need to get the very cold water onto the entire horse as quickly as possible. Again, as long as the water comes off warmer than it went on, keep scraping it off and putting more on. Use the shade, the breeze, and walking to your advantage, and use as many people as you can get to help cool the horse before he suffers medical complications.
The Human Factor
Of course, it does no good to discuss caring for the horse if I don’t also throw in two bits about caring for the rider. On an ECTRA ride, you have no crew available to look after the horse while you go off and lie down, sponge yourself, or eat and drink. DO NOT put the horse’s welfare in front of your own at all costs, since an under-fueled or dehydrated rider can quickly become weak, disoriented, and careless. By forgetting to care for him or herself, a rider can easily jeopardize the welfare and safety of the entire team. You can use the same physics to cool your own body that you use on your horse in extreme weather conditions. Now go out and ride.
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