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The Hot Horse; Anhidrosis to Attitude

The hot horse comes in all shapes and sizes. The summer season opens the door for these physical characteristics to present themselves through encouragement of their development.  The excess heat in the horse’s body can present clinically in many forms from a horse that can’t sweat (anhidrosis), to one with a high strung attitude, skin and eye conditions, and even lameness concerns. To resolve or at least provide better management, it is crucial to understand the problem at its root, as no two horses with heat problems are often addressed the same.

The Hot Horse; Anhidrosis and Attitude
The Hot Horse; Anhidrosis and Attitude

Heat.  It is a rise in core body temperature which can be influenced by many factors.  The summer season gives rise to high external temperatures which are expected to create a rise in the core body temperature, however, for some horses this natural rise is tolerable and in others not so much.  You expect them to sweat, as this is a natural physical defense mechanism to reduce the body temperature, but when sweating is hindered or excessive, it can indicate internal problems.

This internal heat, when excessive influences many functions of your horse’s body.  They aren’t just ‘hot’ in core body temperature, but this internal heat can create manifestations in their body.  These manifestations of excessive internal heat include:

  • Excessive sweating
  • Lack of sweating (anhidrosis)
  • Irritable attitude
  • High strung attitude
  • Skin conditions which are red, inflamed, and irritating
  • Circulatory issues to the foot, joints and muscles, creating a sense of heat to the area
  • Muscular cramps (rhabdomyolysis)
  • Uveitis and other ocular conditions
  • Gastric or stomach ulcers
  • Loose stools with odor
  • Bleeding problems (EIPH or fecal blood)

Think of these horses as having a higher internal core body temperature as a normal state, which can be problematic by itself on a lower level, then expose them to high external temperatures and humidity.  These high outside temperatures add to the already elevated internal core temperature, pushing them over the edge and making physical matters worse.  This is why it is often evident that some clinical problems in the horse seem to disappear in the fall or winter.  The core temperature is often still elevated, despite a lack of ‘fever’, but they are not pushed over the edge by the outside temperatures.  The winter time, due to its cooling nature, will often buffer or soothe the internal heat problem in the horse. However, do not be mistaken in believing that the problem is not still present in your horse.  The problem is still present, but simply put, it is being soothed for the time being and not as obvious.  The problem that comes with this illusion of sorts is that many horse owners stop managing allergies, foot problems or other issues during the cooler times of the year, believing they are not a problem.  In truth, this ‘off-season‘ is the ideal time to manage and get control of those issues when outside influences are not making matters worse.

The Hot Horse, Heat and Inflammation

An elevation of internal heat in the horse is a sign of inflammation, on a scientific level.  The concept of ‘heat’ is taken from alternative medicine philosophies including Ayurvedic and Traditional Chinese Medicine.  A horse can have high internal heat signs, yet not demonstrate a fever clinically.  Others, such as a horse with an acute infection of sorts or “toxic heat”, will have high internal heat and an elevated body temperature clinically.  One is just a progression of another.  A horse with a high internal heat will, over time, develop a mild rise in body temperature when exposed to a high outside temperature, but most will have a normal body temperature when using a thermometer despite being quite irritable, sweating or otherwise.

This ‘heat’ which is present within the body is a signal of inflammation, as inflammation usually coincides with heat on some level, at least on one spectrum.  Inflammation in the chronic phase is often exhausting to the horse, as it is to humans, so it is not uncommon to have a lowered core body temperature just the same.  There are different spectrums to inflammation and it is important to keep this in mind so that you are not misled.

Inflammation is a cellular process where the metabolism of the body is increased and this cellular activity along with hormonal processes can elevate the body temperature.  Due to this inflammatory process, other cellular processes are impacted, some being turned on and some turned off.  The horse’s body is physically hot and this heat must escape.  The heat will dry up fluids (Yin deficiency), alter circulatory patterns in an attempt to dissipate heat, and appear on the surface of the skin with red pustules, papules or vesicles (rash).

This high internal heat will disturb mental faculties, resulting in attitude changes and anxiety.  Due to the drying nature of the heat, it is also common to see acute gastric ulcers in the horse, all due to loss of internal moisture or a yin deficiency.  The immune system can become heightened, over-reacting to almost everything, being then tied in with uveitis and some skin conditions.  The high heat level within the blood can literally boil over at times, weakening blood vessels and resulting in toxic-heat situations where there is bleeding from the lungs (EIPH), in the urine or feces, or skin eruptions that are red and inflamed.

It is not uncommon as well to see flare ups in laminitis cases, increased digital pulses to the feet in general, sore feet, back issues and other joint conditions.  These are all linked with high internal heat and inflammatory changes to the normal blood circulation.  Thus, not uncommon to have a higher incidence of foot concernss, laminitis, and tying-up or rhabdomyolysis in the summer time as opposed to the winter.  Muscle cramps are another clinical manifestation especially in the summer time.

The Origins of Heat in the Horse

A high internal core body temperature in the horse can stem from a variety of causes and is often not the same from one horse to another.  This is crucial to understand as it explains why some horses respond to some therapies, whiles others not so much.  There is a difference between the high internal heat in a Thoroughbred versus a Warmblood or Quarter Horse.  If you address them as being the same, more times than not, the outcomes may not be so favorable.

To understand the origins of heat in the horse is beyond the scope of this article.  I will make an attempt to explain some basic principles, but to truly grasp the concept one must understand alternative medical philosophies.  A basic understanding is offered in our book “Herbs and Whole Foods; Repairing the Horse“.  I would encourage all that are interested to purchase and invest time in reading through this short book.

In Ayurvedic medicine, a situation in which there is excessive heat within a horse would be viewed as a shift towards being Pitta dominant.  The Pitta dosha is more heating by nature and when in excess or out of balance, there is excessive heat produced, along with inflammation. The solution or approach would involve ‘pacifying’ pitta by cooling it down and encouraging other doshas back into balance.

In Traditional Chinese Medicine (TCM), the approach is slightly more complicated but potentially more thorough in understanding.  Let’s look at some basic philosophies in TCM regarding the ‘hot’ horse, outside of an infectious situation.

  • Excess heat produced as a result of Qi or energy stagnation
  • Yin deficiency or lack of internal body moisture to buffer the heat
  • Dampness or digestive concerns creating or contributing to heat
  • Yang excess or provision of heating foods or medications

Now let’s touch base on each of these briefly.  Again, a more detailed explanation is offered in our book mentioned above.

  1. Qi stagnation is a blockage in the proper flow of energy in the horse, usually tied in with emotions or a physical ailment.  This can be seen in the high strung horse with anxiety, the horse pacing the fence line, a stallion worrying over a mare, or a horse pacing or weaving in a stall.  This can also be seen in the horse that is ‘off’ otherwise and irritable, yet forced to work against their will or desire.  The same can be held true for a horse that has pent up hostility due to being confined against their desire.  It is all emotional based and the body reacts.  Additionally, if there is an injury or problem area in the horse, such as a tendon or joint, the natural energy flow will be disrupted and result in stagnation.  This then can contribute to compensatory lameness issues in other areas of the body.  Energy is heat and if you bind or restrict that energy, excess heat will be produced either in the entire body or more localized as in the case of an injury, joint/tendon problem, or foot issues.  If energy or Qi is blocked over a long period of time, then blood circulation can be impacted, resulting in more severe clinical problems.  This called blood stagnation.  Think of the average horse with mild foot pain, yet no digital pulse, which may come and go.  This is Qi stagnation.  Over time, that foot pain becomes more constant and a bounding pulse develops.  This is now blood stagnation and a more severe consequence of the later.
  2. Yin deficiency is a state in which there is a lack of or lower level of internal moisture and coolness to the horse’s body.  Yin is considered more cool and moisturizing, while yang is more heating and drying.  For health and soundness to be optimal, yin and yang must be in balance.  If one is deficient, then the other is in a relative state of excess.  A yin deficiency can be produced naturally due to overwork and physical or mental exhaustion in the horse.  This can also be seen in a horse with a long-term illness or lameness condition which has literally exhausted the horse on a yin level.  This is the most common cause, but there are others.  Keep in mind that a balance must exist and you can supplement too much yang into your horse and create a ‘relative’ yin deficiency just the same. This will be discussed below.  However, the solution or remedy is not the same, so the cause must be differentiated for the best results in your horse.
  3. Dampness (Ama in Ayurvedic medicine) is an accumulation of toxic digestive debris in the horse’s body.  Think of this as being a sponge which is saturated with an oily substance and hard to wring out.  This toxic debris is accumulated over time in most horses but for others it can be more acute.  It is directly associated with the digestive tract and improper functioning on some level and this dampness accumulation can occur anywhere and everywhere in the body.  For some horses, it is seen as an overweight body condition with fat accumulation.  In others, it may show up in the feces with loose stools, odor and mucous streaks.  It could also show up as allergic conditions with an oily type of skin discharge, pus, or other fluid being on the surface of the skin or eyes.  Lymphangitis or stocking up is another manifestation with swollen legs due to fluid accumulation in the subcutaneous tissue.  A final manifestation is the horse with a productive cough with mucous or phlegm.  These are all signs of dampness and compromised digestive function in the horse.  This toxic debris which is accumulating can obstruct normal energy or Qi circulation in the body, resulting in stagnation and hence, heat production as mentioned above.
  4. Yang excess is more common than one might think in the horse.  Yang must be in balance with yin for optimal health and soundness.  As mentioned above, yang is associated with heat and dryness. This excess yang or heat can be produced in the body through provision of grains and improper herb usage in the horse.  All herbs and foods have inherent energies, some heating and some cooling.  Provide the wrong one to your horse and you can create an imbalance with an excess of yang.  Hence, you will see a high predominance of ulcers and bleeding in some horses that are fed high amounts of grains or when using stimulating herbs to enhance performance.  Of course, high outside temperatures such as during the summer time are yang in nature and will add to the existing yang within the horse’s body.  This is not normally a major problem unless the existing yang within the horse is already at a peak level or there is a concurrent yin deficiency, Qi stagnation or dampness already present.  Think of the average race horse fed high quantities of grain, then is stalled most of the day with pent up emotions.

Heat in the Horse; Resolving the Problem

Confused?  Hopefully not.  The problem is really quite evident when you step back, take a breath and think about it.  The solution, however, is not always straight forward.  Keep in mind that no two horses are the same, as no two people are the same.  They each have their own inherent constitution, which dictates energy patterns and condition predilections.  It is more common to have a horse with a few of the above mentioned problems which are contributing to excess heat than it is to just have one, so you have to really assess the situation and every detail that the horse is revealing to you. Address just one factor and improvement may be seen, however, you could also push them further over the edge.  This would be evident in the horse with dampness issues and a yin deficiency as an example.  To resolve or improve the dampness, you would use herbs that help to remove fluid or toxic accumulation from the horse’s body, which can be like through a diuretic type of effect.  If you just do this part, removing dampness, then you could contribute further to the yin deficiency state, adding more heat to the equation.  Additionally, if you just supplemented the yin component, you could add to the dampness issue in the horse as yin herbs and foods can be somewhat heavy to digest and add additional stress to an already stressed digestive system.

Again, these concepts are discussed in more detail in our book, “Herbs and Whole Foods; Repairing the Horse.”

In part two of this article, I will touch base on some approaches from diet to herbal use which can greatly improve the hot and inflamed horse.

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Author:  Tom Schell, D.V.M, CVCH, CHN




1 thought on “The Hot Horse; Anhidrosis to Attitude”

  1. I’m in the UK and have a horse with anhidrosis. It’s definitely starting to affect her feet and she’s been footsore this year for the first time. Very interested in part 2!

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