A herd of feral horses drinking.1
How a horse drinks
We are accustomed to watching dogs drink, and know that they somehow scoop it up with their tongues. We haven’t watched very closely, though, because we learn that dogs don’t scoop at all. They curl their tongues backward, push them into the water, lift them quickly, and a column of water is pulled up by momentum, not scooped up. They then snap their jaws closed on this column of water — effectively biting it — and swallow. Your cat doesn’t drink the same way as your dog,2 even though neither has a full set of cheeks. And your horse? Not like a dog, not like a cat, but like a human. He sucks the water in. Elephants do the same, but they suck it in with their nose, then blow it down the hatch.
Heat Buildup, Heat Loss
The surface area of a horse determines how fast it can cool. Its weight determines how fast it can heat. This principle tells us how well a homeothermic (warm-blooded) animal is adapted to hot or cold climates, and is called Allen’s rule.
Allen’s rule helps account for why rabbits in the desert have longer ears than those in the Arctic. It helps account for why Polar bears have stockier limbs and shorter ears than the Brown bears from which they are descended.
Hot bloods developed in hot places, and their primary problem was heat buildup. So they developed long legs and smaller bodies. They stand tall. Cold bloods developed with a primary problem of heat loss. So they developed shorter legs and stockier bodies. With this design, the hot bloods have horse power, the cold bloods have torque.
The horse’s lungs can serve as a radiator during exercise. One study3 found that during exercise, about 19-30% of the heat a horse produces is lost through respiration:
- When exercising at 40% of his maximum omaximum oxygen uptakemaximum oxygen uptake until moderately fatigued (about 38 minutes), a horse’s respiratory heat loss as been estimated at 30% of the heat produced by the exercise.
- If exercised at 65% of his maximum oxygen update until moderately fatigued (about 15 minutes), respiratory heat loss as been estimated at 19% of the heat produced by the exercise.
- If exercised at 40% of his maximum oxygen update until moderately fatigued (about 9 minutes), respiratory heat loss as been estimated at 23% of the heat produced.
The heat produced by exercise is not all dissipated during exercise. One study4 found that between 7-20% of the heat a horse produced still remained in the horse half an hour after exercise ended. Another study5 of thoroughbreds found that after a 1,600 meter (1 mile) race, it took a full hour after a race for the horse’s body temperature to return to normal. After exercise, a horse may continue to sweat to remove this heat.
Sweat arrives at the skin hot, at the horse’s body temperature. When it evaporates, it takes the heat with it — evaporative cooling. Toweling or scraping a sweaty horse will interfere with his cooling, because the sweat that has been removed with the towel cannot evaporate to cool him.
Because evaporation is critical to the cooling effect of sweat, there are obvious factors that affect its value. If there is a fan, good air circulation, or low humidity, then sweat will evaporate faster, cooling faster.
A horse that does not feel thirst will not drink. Thirst, it turns out, comes from an increase in “plasma osmolality”, specifically an increase in the concentration of plasma sodium. So, as a horse dehydrates, the concentration of plasma sodium goes up, and he feels thirsty.
Not many animals sweat, but horses and certainly humans do. Your horse will sweat under many conditions — an endurance ride, a trail ride on a hot day, eventing, polo or polocross. And he will lose water in his poop — about 3/4 of his poop is actually water.6
During strenuous endurance exercise, such as distant running, a human athlete might lose about 2% of their body weight, most of this coming from fluid loss by sweating.7 Horses seem to lose even more. Studies of endurance horses show them losing 3-4% of their body weight in sweat (one study reports water losses of 7.8% to 15.3% of body weight!8 The exercising horses were allowed to drink during their exercises; at the end of the exercises, the deficit in total body water was about 8.5%). Water losses can persist despite frequent access to water during the exercise and an after an overnight recovery period.9
One study10 exercised horses at low intensity through three 15 km (9.3 miles) courses running at about 40% of maximal oxygen uptake. They report a number of interesting findings:
- Sweating increased rapidly for the first 20 minutes of exercise, but then remained constant.
- The longer a horse exercised, the more sodium, calcium and potassium it lost through sweat.
- The concentration of sodium and calcium in sweat increased until the horse had been exercising 30 minutes, then remained constant. The concentration of potassium lost through sweat diminished during the exercise.
- While covering the 45 km (28 miles), the horses lost about 33.8 liters of fluid — about 9 gallons. This was about 11% of the horse’s total body water.
If you are planning on exercising your horse for twice this distance, you shouldn’t assume that he will lose twice as much fluid through sweat. As an animal’s fluid reserves diminish, it raises the threshold for sweating to begin.11 In endurance events of 48-163 km (30-100 miles), the majority of fluid lost through sweat will occur in the first half of the event.12 Your horse will run hotter and hotter, but not get sweatier and sweatier as he loses fluids.
Drinking both assesses dehydration and reduces it. You can measure latency to investigate (sec), latency to first drink (sec), volume drunk in 10 min, time spent drinking (sec), number of drafts taken, how time from start until he has finished his last draft (min). All of these should correlate, so use any as your standard measure.
When you or your horse sweats, you lose both water and electrolytes — sodium, potassium, calcium, bicarbonate, magnesium, chloride, and hydrogen phosphate. Electrolytes produce an electrically conducting solution when dissolved in water, and are critical to the operation of nerves and muscles. Because electrolytes are lost through sweat, neither you nor your horse may experience much of an increase of plasma sodium, and after a tough workout, in which you have sweated profusely, you may not feel thirsty. But if you have sweated hard, you are now short on both water and electrolytes.
Electrolytes are important for hydration, among other things. For your gut to absorb water, it depends on absorption of solutes such as sodium. The overall process is not dumb like a sponge, but active and selective. The small intestine absorbs all electrolytes, and secretes bicarb. The large intestine absorbs sodium and chlorine, and secretes potassium and bicarb. The colon spits out potassium. Throughout, the intestinal wall both absorbs and secretes each electrolyte, depending on its concentration in the body’s fluids.13
There are several different mechanisms by which certain electrolytes are moved. Sodium, for instance, is transported with glucose and amino acids into the cell; if a cell contains too much sodium, then a sodium pump removes it from the cell. Much of this exported sodium finds itself in the spaces between cells. The concentration of sodium in those spaces creates an “osmotic gradient” that draws water in.14 (Sounds like the basis of thirst, doesn’t it?)
If you give your horse too much of some electrolyte, some will be absorbed and some will be passed on and out. Your body is not merely selective for “electrolytes” but for specific electrolytes, so it will grab all the magnesium it can get if you are short on magnesium, and not show much interest in sodium if you have plenty of that. Beyond the gut, the kidneys are in charge of grabbing any excess in specific electrolytes in your body, and sending them out.
A Gatorade may work in the same way: a 12 ounce bottle contains 10% of the average adult’s daily sodium requirement. So despite what you may have read online about giving your horse a Gatorade, everything in it is either good for him (sodium chloride, sodium citrate, monopotassium phosphate) or neutral (citric acid, natural flavor, flavoring and coloring) except for the sugar (sucrose and dextrose). If you are going to give your horse Gatorade, don’t pour it into his water. He’ll have to drink the entire bucket before extracting the meager benefits from a bottle of it. And because the ratios of electrolytes don’t correspond to the ideal levels of electrolytes in his body, and aren’t designed to match what he loses through sweat, Gatorade seems to be an expensive alternative to electrolyte paste, one which delivers lower bang for the buck. (Your horse may buck without banging at all, in fact.)
G2 contains similar ingredients: some good (sodium chloride, sodium citrate, monopotassium phosphate) some neutral (citric acid, natural flavor, flavoring and coloring) but some not desirable: the sugars and sweeteners (high fructose corn syrup, sucrose syrup, sucralose (”Splenda”) and acesulfame potassium (an artificial sweetener that provides some potassium). So G2 may be fine for you, but not a good way to spend your horse’s allowance.
Offering electrolytes for ad lib consumption is a great idea if your horse is cooperative. You can offer electrolyte powder (Amazon carries dozens of products) in a bucket at a rest stop and after an event, or hang such a bucket in his stall full time. You might also slip a teaspoon of it in a glass of water, and see whether you can stand the flavor. Your body can make do with electrolytes for a horse just fine.
If your horse does not eat the powder promptly on a short rest stop, then you might offer electrolyte paste. This stuff comes in a syringe, and can be squirted into his mouth. He’ll swallow the salty stuff and want a drink. Presto. Problem solved.
There is research indicating the electrolyte paste works. A team of researchers led by Harold Schott15 have found that any of the electrolyte pastes they tested resulted in significantly greater voluntarily water intake, compared with a control treatment (no paste). When sodium chloride (table salt) was a component of the paste, horses recovered significantly more body weight. When given a paste, horses first became hyperhydrated, but then also increased their urination and electrolyte excretion. No adverse effects of the administration of electrolyte pastes was observed. Other studies have found that electrolyte pastes help with rehydration.16
Leading a Horse to Drink
Horses may get more dehydrated than humans, though, because their sweat contains a higher concentration of sodium than that found in human athletes.17 Because they lose more sodium than we do, their sense of thirst isn’t so strong — because the concentration of their plasma sodium has not changed much.
But don’t trust your horse. Drinking is not enough for recovery. Drinking will take a horse from hypertonicity to isotonicity — that is, he’ll drink until his electrolyte balance returns to normal. But because he has lost electrolytes through sweat, when he stops drinking, he’ll be short on both electrolytes and water, even though what he has inside is now in balance.
Without thirst, there isn’t drinking. You can lead him to water, but without thirst you can’t make him drink.
You can trick him into drinking. Many suggest providing an oral electrolyte paste. This stuff may replace some of the electrolytes he has lost through sweat, but it will also increase his plasma sodium. With an increased concentration of sodium, he’ll feel thirst and drink.
A variation on this trick: add to his thirst by offering water that contains some of the salt he needs, along with fresh water. Provide him with a gallon of water into which you’ve added a teaspoon of electrolytes (or sea salt or table salt.) When he drinks the somewhat salty water, he will both replace his water and replace his electrolytes. If in the course of drinking the salty water he becomes hypertonic and thirsty, he can solve his problem by drinking fresh water that you will separately provide.
Your horse may know when he is short on electrolytes, so at the same time that your are providing water, provide a bucket of electrolytes.
If you will give your horse a bucket of salted water, don’t overdo the salt. Mix up a quart or two, and taste it first. If it tastes a little salty, it is OK. If tastes like a swim in the ocean, you may be OK. But if it tastes like something from the Great Salt Lake, dilute it and taste it again before sharing it with him. Too much salt can be a very bad thing. Salt poisoning, also known as hypernatremia, occurs when a body takes in dangerously high levels of sodium. Too much sodium in the bloodstream can cause trouble breathing, damage kidneys, trigger nausea, vomiting and weakness, damage brain cells, and lead to seizures, coma or even death. Not surprisingly, too little salt is bad as well. Called hyponatremia, it occurs when a body’s sodium falls dangerously low. Symptoms include a decreased ability to think, headaches, nausea, and poor balance. Severe symptoms include confusion, seizures, and coma. (I already suffer from a reduced ability to think, poor balance, and confusion. But I think this is caused by something else.)
What are normal levels of sodium in the blood? Levels usually measured in millimoles, and reported in a form showing concentration per liter, as “145 mmol/L”. Sometimes they are measured as milliequivalents, and reported in the form “145 mEq/L). In humans: “Normal serum sodium levels are 135–145 mmol/L (millimoles per liter)(135–145 mEq/L). Hyponatremia is generally defined as a serum sodium level of less than 135 mmol/L and is considered severe when the level is below 120 mmol/L.”
Which begs the question: how much salt? No one seems to know, so here is my dodgy math…
- We have learned that your horse can lose 3-4% of his body weight in sweat after an all-day hard ride which includes as much water as he will drink. Suppose your horse weighed 1000 pounds at the starting line. At the finish line, he will have lost 30-40 pounds of sweat. (If you are trying to translate my logic to your horse, determine what fraction of a 100-mile endurance ride he has completed, and get an estimate on his weight. Then do your own math.)
- Not all electrolytes are passed from the body into sweat at equal rates. Sweat is dominated by sodium chloride,18 but also contains high levels of potassium chloride, calcium, and magnesium.19
- You will want your horse to rehydrate, so that if he loses 35 pounds of water in sweat, he should drink that much water — about 4.2 gallons.
- If you can get him to drink that much water, then all you’ve got to do is get him to imbibe the electrolytes he has lost. Horse will self-regulate — if he needs salt, he’ll eat it if he can get it. While you can do this with some oral injections of electrolyte paste, I’d prefer to let my horse dose himself. You can do this by providing him with Red Cal,20 which both my horse and mule recommend. This is a powdered mix with the consistency of sand. Put it in a bucket on the wall of his stall, and walk away. Check it from time to time — if he poops in it, he will stop eating it.
Dehydration results from the difference between thirst and water deficit. If a horse feels thirsty, and has access to water, he will drink until his feeling of thirst abates, and rehydrate. If a horse does not feel thirsty, he will not drink.
Thirst comes from hypertonicity21 — when the ratio of salt and fluid in the body is higher than normal. It is excess salt that triggers thirst. But if your horses has sweated, he has lost both salt and water, and his thirst will be inadequate to restore his normal fluid level. (And of course, drinking water alone doesn’t restore electrolytes lost in sweat.)
You’ve gone for a long ride. Your horse has been sweating. Is he dehydrated? You don’t have the option of analyzing his packed cell volume, serum total protein, electrolytes and osmolality.22 You can’t determine changes in your horse’s weight during his exercise.23 You simply don’t know how much fluid he has lost through respiration, sweat, and urination, or how much he has replaced by drinking.24 In fact, if he is dehydrated, you don’t even know whether he is experiencing isotonic dehydration (he has lost a comparable level of water and electrolytes as that found in his blood) or hypotonic dehydration (some water loss and a considerable loss of electrolytes). If your horse has worked hard for an hour or so without a drink, his problem is likely isotonic dehydration. If he has worked for several hours, and you’ve allowed him access to water at intervals, then he may be experiencing hypotonic dehydration.
Mucous membrane dryness. Maybe we could assess mucous membrane dryness. It is well known that when we become dehydrated, our mucous membranes become dry. Would a measurement of this dryness in our horse work? Nope. Researchers25 have found that membrane dryness — as measured by the size of a wetted area when a square of fast filter paper was placed on the gums above the upper corner incisor — was unrelated to either water intake or electrolyte level. So forget that.
Skin tent test. Trying to come to the rescue is the skin tent test: the skin is pinched on the neck, point of the shoulder, or (shudder) eyelid, and the observer determines how long, in seconds, it takes to return to its normal position. The skin tent test is used to assess skin turgor — the skin’s propensity to rapidly return to its normal contour after being raised in a fold pinched between an examiner’s thumb and forefinger. The theory is that the tent takes longer to return to its normal position when the horse is dehydrated, though researchers have long known that it is also affected by age. Get old enough, and the skin never returns to it original position — even without a tent test.
This test has been in use for a very long time, and may have been first added to the scientific literature in 198126 or earlier. The test a very popular measure of dehydration, and widely endorsed. Read about it in stories like “Simple tests ensure horse is well hydrated”27, “Dehydration: It Happens To Horses Too”,28 “How to Assess A Horse’s Hydration with Skin Pinch on Shoulder …”29, “Assess Hydration with Skin Pinch on Shoulder”30, “The Equine Physical Exam – 120 Seconds and $0”31, and on and on…
But it turns out the skin tent test is not a good measure of dehydration. In 2008, four researchers carefully studied the state of horse dehydration as measured in various ways, and how the actual state of dehydration matched with the results of tenting.32 They found that skin tent duration was neither a valid nor repeatable indicator of dehydration. Their research led to a number of important findings:
- Skin tent duration is affected by side of animal, anatomical location, coat moisture, and age. Another study has found that an animal’s weight also contributes to tent duration.33 Thus many factors besides dehydration muddy our conclusions from tent duration.
- There was no significant association between skin tent duration and blood plasma osmolality — the horse’s electrolyte balance. A horse that has lost a lot of electrolytes through sweat will not be any thirstier than one who has not, nor will the electrolyte balance be reflected in skin tent duration.
- Horses with long skin tent durations do not drink more water than those with shorter durations. Horses do not reveal their need for hydration through skin tent duration.
- Water consumption by the horse is a good indicator of dehydration. Providing clean water for ad lib consumption is a good way to both measure dehydration and to reduce it. Horses with a higher electrolyte level drank significantly more water, and had longer and more frequent drinking bouts.
So, no. Skin tent tests appear worthless, despite widespread acclaim for them. There is now lots of research which confirms that such tests are not valid or reliable.34
Rectal Temperature and Respiratory Rate.
The researchers who found that the skin tent test was worthless as a measure of dehydration have also found that rectal temperature and respiratory rate are good indicators of heat stress35 (which I grant is a bit different than dehydration.) The table below shows that donkeys and horses showing signs of heat stress had significantly higher rectal temperatures and respiratory rates than those not showing heat stress. They also measured heart rates, and while heart rates tended to be higher in horses and donkeys with heat stress, the difference was not significant.
Associations between heat stress behavior and clinical parameters in 130 working horses and donkeys.36
You should know your horse or mule’s normal rectal temperature, so that you can compare it whenever you are concerned about heat stress or dehydration. Normal temperature for a “normal horse” may be 99.5-102.1°F / 37.5-38.9°C37 Your horse might vary, so know his rectal temperature — or temperature range — exactly by measuring him several times when he is at rest, prior to exercising him hard. Take his rectal temperature using a digital thermometer that’s been dipped in a small amount of lubricant. Use a string or hang on to it, so you don’t lose it up his rectum!
I believe that your horse’s temperature measured on his ear or forehead should correspond to his rectal temperature (it will likely be lower, but it should be meaningful.) If you don’t want to stick something up his butt, or want to measure his temperature while you are riding, consider something like a modern forehead thermometer, such as an Innovo Medical Forehead and Ear Thermometer.38 Such products can be found on Amazon for under $35, and could be used while in the saddle. Experiment with him first, at rest, before trusting this approach.
You should also know your horse or mule’s normal respiratory rate when he is at rest. Normal rates for adult horses are 8-24 breaths per minute (lower than the horses or donkeys in the table above regardless of heat stress.) You’ll want to know this exactly, too, having measured it several times when he is relaxed. Measure his rate by standing next to him, and counting how many times his chest rises in one minute. You might try a small mirror held at his nose, to see if watching the moisture condense and evaporate is any easier.
When your horse has generally recovered, his temperature will be normal (for him), his respiration rate normal (for him), and he will have lost interest both in drinking and electrolytes.
Your horse’s coat is nearly waterproof. It will take a lot of rain before his skin gets wet. This is good. But when he sweats, the sweat will be trapped by this wondercoat, and not evaporate well. When it doesn’t evaporate, it doesn’t cool him.
Your wonderhorse deals with the heat-trapping properties of his wondercoat with the magic of latherin — a protein that serves as a wetting agent, detergent and foaming agent.39 Once latherin has worked its way through his coat, the coat now fails to trap his heat, and his sweat can evaporate more easily. Latherin is probably evenly distributed throughout a horse’s sweat, but you’ll be able to see it wherever the skin has been rubbed. From the rider’s standpoint, this might be yucky, but for Mr. Horse, it helps a lot with cooling. Until he has cooled down from his workout, leave the latherin on.
Latherin produced by a hot horse. Because the horse was clipped, the latherin has concentrated at the saddle pad, where the horse could not sweat. Other areas seem fairly free of latherin. A common place to find latherin is between the haunches, which heats up more than the horse’s outer surface because there is less air circulation here.40
Frequency and duration of drinking
How often to horses drink? How long do they drink? Three researchers41 studied the drinking of 11 mares and 15 foals living on pasture with free access to water. These researchers toiled away, monitoring this group for 2,340 15-minute intervals — a total of 585 hours of observation. Among their findings:
- Movement to water sources was frequently, but not invariably, carried out by an entire herd. With their heads down, horses are at greater risk of predation when drinking, and the comfort of the herd is likely sought.
- Frequency but not duration of drinking bouts by mares increased as the temperature increased. Frequency was greatest at 30 to 35 C, at which temperature mares drank once every 1.8 h. Given a finite capacity of the stomach, and given a constant rate of swallowing, this strategy makes sense when fluids are being lost through respiration and sweat.
- Frequency of drinking varied with the time of day, being rarest during the early morning (0500 to 0900 h) and most frequent during the afternoon (1300 to 1700 h). Preferred drinking times coincide with changes in temperature during the day.
- Drinking by foals was very rare. The youngest age at which a foal was observed to drink was 3 wk, and 8 of 15 foals were never observed to drink before weaning.
Feral foal drinking.42
How much does your horse drink? It is likely that he drinks between 5 and 10 gallons a day. But he’ll need more if he is exercising, or if he is hot, or if she is pregnant or lactating.
Notes for a Cooler
This chapter is about drinking, but it turns out that much of drinking relates to sweating, which relate to cooling. If your horse did not heat up during exercise, he wouldn’t need to sweat, and so his fluid requirements would be about the same as they are when he is standing in his stall.
Here is my idea for how to cool your horse on a long hard ride. Our gizmo is an adaptation of a handheld misting fan. Such devices spray very fine drops of water. We will direct the spray to our horse’s skin, and a fan will move air that helps our spray — and any sweat — to evaporate. The water on the horse’s skin absorbs heat as it turns to a gas — evaporative cooling — and cools him.
Our goal is to reduce the need for sweating. We will choose the target — a small area of the horse’s surface where heat builds up, and which we will cool. This might be the groin area, where latherin is so often found. Ideally, we will carefully shave this area, so that our misting treatment is of skin, rather than fur.
To replace the sweat, we will add a bit of water of our own to the target surface. This water might be carried in plastic tanks — one in each of two saddle bags on the haunches, resting on a breathable pad43 to maximize air flow. It might begin your workout as ice water, which will cool him better than warm water (because water must be raised to a vapor point to evaporate, and cold water will need to draw more heat from his body to reach this point).
To improve the wetting ability of the water, a small amount of a surfactant or detergent might be initially mixed with the water, to allow the passage of the spray to the skin if it is to be sprayed on an unshaved area. I recommend Dawn dish washing liquid. International Bird Rescue conducted some research,44 and uses Dawn for rescuing oiled birds because it has the ability to remove most oils, is effective in low concentrations, is non-irritating to the skin and eyes, rinses quickly, is inexpensive, and is widely available. Whatever you use, monitor for for allergic reactions!
Water will be applied as a fine mist. A small sprayer might be an adaptation of a backpack sprayer originally designed for spraying herbicides and fertilizers. But much simpler and lighter weight would be a small sprayer that is powered by a hand pump. Many such devices are available online for under $20.45 A short blast of the sprayer would wet the target surface with a thin layer of moisture.
Knowing that it is not sweat that cools, but the evaporation of sweat, we add a small fan that will assist in the evaporation of what we have sprayed, and any sweat that has been produced in the target area. This fan could be battery powered, of course. But a bladder placed under your saddle, with inlet and outlet valves, could do the job. Each time you come down in the seat, your weight would force air out of the bladder, and through a tube to the area we are cooling. On each rise from the saddle, the bladder would take in air from its inlet valve. So you’d produce one small blast of air with each contact with the saddle. We’ll call this the gas bag, in honor of your author. The fan or gas bag will ensure that surface moisture evaporates promptly, even on a hot day with high humidity and no breeze.
How does our contraption attach to our horse?
I think a good way might be to hang the fan from a rear flank cinch. The fan would hang from this cinch, run on batteries, and direct its air flow back toward the groin. It would be turned on at the beginning of the ride, and off at the end.
Airline tubing would run down from your two water containers in your saddle bags.
To get started in this project, you might simply get a battery-powered water misting fan with a protective grill over both sides of the fan,46 connect it to hang from a rear flank cinch, and give it a try. If your horse appears to sweat less, you are on the right track. Try a little science — perhaps take a twenty minute ride with the mister, then a twenty minute ride without the mister. Measure and record his temperature and respiratory rate before and after each comparison. A handheld mister can keep you cool on a hot day. It should work on your horse.
1 image source: Ransom, Jason I., and Brian S. Cade. “Quantifying Equid Behavior–A Research Ethogram for Free-Roaming Feral Horses.” U.S. Geological Survey Techniques and Methods 2-A9, 23 p. (2009) http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1018&context=usgspubs
2 Pantaleo, Rick. “Think you know how dogs drink water?” http://learningenglish.voanews.com/a/how-do-dogs-drink-water/3116091.html
3 Hodgson, D. R., Laura Jill McCutcheon, Sherell K. Byrd, William S. Brown, W. M. Bayly, G. L. Brengelmann, and P. D. Gollnick. “Dissipation of metabolic heat in the horse during exercise.” Journal of Applied Physiology 74, no. 3 (1993): 1161-1170.
4 Hodgson, D. R., Laura Jill McCutcheon, Sherell K. Byrd, William S. Brown, W. M. Bayly, G. L. Brengelmann, and P. D. Gollnick. “Dissipation of metabolic heat in the horse during exercise.” Journal of Applied Physiology 74, no. 3 (1993): 1161-1170.
5 Hassan, Hany Y., Mahmoud A. Aly, Youssef M. ELseady, Mohamed A. Nayel, Ahmed M. Elsify, Akram A. Salama, Mohamed S. Hassan, Emad F. Elbarody, and Ahmed B. Kamar. “The Effect of Race in the Clinical, Hematological and Biochemical Biomarkers in Thoroughbred Horses.” Alexandria Journal of Veterinary Sciences 46, no. 1 (2015): 161-169.
6 Tanaka H., Osaka Y., Obara S., Yamaguchi H., Miyamoto H. (1992) Changes in the concentrations of Na+, K+ and Cl− in secretion from the skin during progressive increase in exercise intensity. Eur. J. Appl. Physiol. 64:557–561
7 Greenleaf, J.E. (1992) Problem: thirst, drinking behavior, and involuntary dehydration. Med. Sci. sports Exerc. 24, 645-656.; Szlyk, P., Sils, I.V., Francesconi, R.P., Hubbard, R.W. and Armstrong, L.E. (1989) Effects of water temperature and flavoring on voluntary dehydration in men. Physiol. Behav. 45, 639-647.
8 Kingston, Janene K., Raymond J. Geor, and Laura Jill McCutcheon. “Rate and composition of sweat fluid losses are unaltered by hypohydration during prolonged exercise in horses.” Journal of Applied Physiology 83.4 (1997): 1133-1143.
9 Düsterdieck, K.F., Schott, H.C., Eberhart, S.W., Woody, K.A. and Coenen, M. (1999) Electrolyte and glycerol supplementation improve water intake by horses performing a simulated 60 km endurance ride. Equine vet. J., Suppl. 30, 418-424.; Kingston, J.K., Geor, R.J. and McCutcheon, L.J. (1997) Use of dew-point hygrometry, direct sweat collection, and measurement of body water losses to determine sweating rates in exercising horses. Am. J. vet. Res. 58, 175-181. ; Schott, H.C., McGlade, K.S., Molander, H.A., Leroux, A.J. and Hines, M.T. (1997)
Bodyweight, fluid and electrolyte, and hormonal changes in response to 50 and 100 mile endurance rides. Am. J. vet. Res. 58, 303-309
10 Kingston, Janene K., Raymond J. Geor, and Laura Jill McCutcheon. “Rate and composition of sweat fluid losses are unaltered by hypohydration during prolonged exercise in horses.” Journal of Applied Physiology 83.4 (1997): 1133-1143.
11 Montain S. F., Latzka W. A., Sawka M. N. (1995) Control of thermoregulatory sweating is altered by hydration level and exercise intensity. J. Appl. Physiol. 79:1434–1439; Sawka M. N., Young A. J., Francesconi R. P., Muza S. R., Pandolf K. B. (1985) Thermoregulatory and blood responses during exercise at graded hypohydration levels. J. Appl. Physiol. 59:1394–1401.
12 Ecker, G. L., and M. I. Lindinger.Effects of terrain, speed, temperature, and distance on water and ion losses. Equine Vet. J.,Suppl. 18: 298–305, 1995.; Lindinger, M. I., and G. L. Ecker. Ion and water losses from body fluids during a 163 km endurance ride.Equine Vet. J.,Suppl. 18: 314–322, 1995.
13 See Sidorov, J. J. “Intestinal absorption of water and electrolytes.” Clinical biochemistry 9 (1976): 117-120.; Turnberg, L. A. “Electrolyte absorption from the colon.” Gut 11.12 (1970): 1049-1054.; Krattenmacher, R., R. O. S. I. T. A. Voigt, M. Heinz, and W. Clauss. “Electrolyte transport through a cation-selective ion channel in large intestinal enterocytes of Xenopus laevis.” Journal of experimental biology 155, no. 1 (1991): 275-290.
14 Bowen, R. “Absorption of Water and Electrolytes” Oct 22, 1995 http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_water.html
15 Schott II, Harold C., Shannon M. Axiak, Kristina A. Woody, and Susan W. Eberhart. “Effect of oral administration of electrolyte pastes on rehydration of horses.” American journal of veterinary research 63, no. 1 (2002): 19-27.
16 Sosa León LA, Hodgson DR, Carlson GP, et al. Effects of concentrated electrolytes administered via a paste on fluid electrolyte and acid base balance in horses. Am J Vet Res 1998;59: 898–903. 13. Düsterdieck KF, Schott HC, Eberhart SW, et al. Electrolyte and glycerol supplementation improve water intake by horses performing a simulated
17 Convertino, V.A., Armstrong, L.E., Coyle, E.F., Mack, G.W., Sawka, M.N., Senay, L.C. and Sherman, W.M. (1996) Position stand: exercise and fluid replacement. Med. Sci. sports Exerc. 28, i-vii.; McCutcheon, L. J., and R. J. Geor. “Sweat fluid and ion losses in horses during training and competition in cool vs. hot ambient conditions: implications for ion supplementation.” Equine Veterinary Journal 28, no. S22 (1996): 54-62.
18 Robinson, Sid, and Aline H. Robinson. “Chemical composition of sweat.” Physiological reviews 34.2 (1954): 202-220.
19 Kerr, M. G., and D. H. Snow. “Composition of sweat of the horse during prolonged epinephrine (adrenaline) infusion, heat exposure, and exercise.” American journal of veterinary research 44.8 (1983): 1571-1577.
20 Read more about this product at TheNaturalVet.com
21 Johnson, Philip J. “Physiology of body fluids in the horse.” The Veterinary clinics of North America. Equine practice 14, no. 1 (1998): 1-22.
22 These methods are discussed by Brownlow, M.A. and Hutchins, D.R. (1982) The concept of osmolality: Its use in the evaluation of “dehydration” in the horse. Equine vet. J. 14, 106-110.
23 This method is discussed by Carlson, G.P. (1987) Haematology and body fluids in the equine athlete: A review. In: Equine Exercise Physiology, Eds. J.R. Gillespie and N.E. Robinson, ICEEP Publications, Davis. pp 393-425.
24 This method is discussed by Kingston, Janene K., Raymond J. Geor, and Laura Jill McCutcheon. “Rate and composition of sweat fluid losses are unaltered by hypohydration during prolonged exercise in horses.” Journal of Applied Physiology 83.4 (1997): 1133-1143.
25 Pritchard, J. C., C. C. Burn, A. R. S. Barr, and H. R. Whay. “Validity of indicators of dehydration in working horses: a longitudinal study of changes in skin tent duration, mucous membrane dryness and drinking behaviour.” Equine veterinary journal 40, no. 6 (2008): 558-564.
26 Dorrington, Keith L. “Skin turgor: do we understand the clinical sign?.” The Lancet 317, no. 8214 (1981): 264-266.
27 The Western Producer. http://www.producer.com/2014/08/simple-tests-ensure-horse-is-well-hydrated/
28 Equinews www.equinews.com/article/dehydration-it-happens-to-horses-too
30 Horse Side Vet Guide. http://horsesidevetguide.com/drv/Skill/10/assess-hydration-with-skin-pinch-on-shoulder/
31 Irongate. irongateequine.com/equine-physical-exam/ and on and on.
32 Pritchard, J. C., C. C. Burn, A. R. S. Barr, and H. R. Whay. “Validity of indicators of dehydration in working horses: a longitudinal study of changes in skin tent duration, mucous membrane dryness and drinking behaviour.” Equine veterinary journal 40, no. 6 (2008): 558-564.
33 Pritchard, J. C., A. R. S. Barr, and H. R. Whay. “Validity of a behavioural measure of heat stress and a skin tent test for dehydration in working horses and donkeys.” Equine veterinary journal 38, no. 5 (2006): 433-438.
34 Pritchard, J. C., A. R. S. Barr, and H. R. Whay. “Repeatability of a skin tent test for dehydration in working horses and donkeys.” Animal Welfare — Potters Bar then Wheathampstead – 16, no. 2 (2007): 181.; Pritchard, J. C., A. R. S. Barr, and H. R. Whay. “Validity of a behavioural measure of heat stress and a skin tent test for dehydration in working horses and donkeys.” Equine veterinary journal 38, no. 5 (2006): 433-438.
35 Pritchard, J. C., A. R. S. Barr, and H. R. Whay. “Validity of a behavioural measure of heat stress and a skin tent test for dehydration in working horses and donkeys.” Equine veterinary journal 38, no. 5 (2006): 433-438.
36 Table from Pritchard, J. C., A. R. S. Barr, and H. R. Whay. “Validity of a behavioural measure of heat stress and a skin tent test for dehydration in working horses and donkeys.” Equine veterinary journal 38, no. 5 (2006): 433-438. Page 435.
37 “Normal Horse Temperature, Heart Rate, Breathing Rate” The Horse. Aug 22, 2011. http://www.thehorse.com/articles/27822/normal-horse-temperature-heart-rate-breathing-rate
38 Find this product here: https://smile.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=%22Innovo+Medical+Forehead+and+Ear+Thermometer%22
39 For a closer look at latherin, see McDonald, Rhona E., Rachel I. Fleming, John G. Beeley, Douglas L. Bovell, Jian R. Lu, Xiubo Zhao, Alan Cooper, and Malcolm W. Kennedy. “Latherin: a surfactant protein of horse sweat and saliva.” PloS one 4, no. 5 (2009): e5726.
40 Image source: https://www.google.com/imgres?imgurl=http%3A%2F%2F68.media.tumblr.com%2F6e4414a6d6e2f3e42d2d81e70a8d8f96%2Ftumblr_ns9akcrQPG1sg2in4o2_1280.jpg&imgrefurl=http%3A%2F%2Ftheclassicalhorse.tumblr.com%2Fpost%2F125390217739%2Fmievzar-spiffypony-theclassicalhorse-i&docid=LLVAjnhS6Db9XM&tbnid=CiTDLhPFVUuOhM%3A&vet=1&w=1280&h=960&bih=734&biw=1536&ved=0ahUKEwie3K39x6HSAhXq6oMKHVTJA1sQMwgfKAMwAw&iact=c&ictx=1#h=960&imgrc=CiTDLhPFVUuOhM:&vet=1&w=1280
41 Crowell-Davis, Sharon L., Katherine A. Houpt, and Joyce Carnevale. “Feeding and drinking behavior of mares and foals with free access to pasture and water.” Journal of animal science 60, no. 4 (1985): 883-889.
42 image source: Ransom, Jason I., and Brian S. Cade. “Quantifying Equid Behavior–A Research Ethogram for Free-Roaming Feral Horses.” U.S. Geological Survey Techniques and Methods 2-A9, 23 p. (2009) http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1018&context=usgspubs
43 You’ll find many breathable pads online. Equipedic claims EquiKool pad offers the most breathability, but you do your own research. Start here, perhaps: http://www.equipedic.com/Breathe_Ability_Comparisons.htm
44 International Bird Rescue. “Our Process for Helping Oiled Birds”. https://www.bird-rescue.org/our-work/aquatic-bird-rehabilitation/our-process-for-helping-oiled-birds.aspx
45 For instance, the O2Cool Water Misting Fan here: https://www.amazon.com/O2COOL-FML0001-Misting-Portable-Handheld/dp/B01G70E2OQ For a nice selection, see https://www.walmart.com/c/kp/water-misting-fans
46 Here’s a fan and mister that looks ready for your adaptation: https://smile.amazon.com/Portable-Handheld-Humidifier-Hydrating-Rechargeable/dp/B01FC8COA8/