Oct 112023

Equine Hypothyroidism-The Under Estimated Ilness of the Endocrinal System.

Copyright by C. Cooper Lic Ac CVA, CVHM.
All rights reserved.
No portion of this publication may be used without prior written permission of the author. The author asserts her moral right to be identified with this work.

“You can’t connect the dots looking forward; you can only connect them looking backwards. So you have to trust that the dots will somehow connect in your future.”

                                                                      -Steve Jobs-


In all my years of treating horses it has taken me considerable time to determine “What lies beneath” the many layers of presenting symptoms one sees in practice and the underlying factors associated with so many different illnesses in horses these days.

In my opinion the key is to treat the disease from the core issues that are the causative factors. Peeling the onion to get to the core, but the core problem is often the hardest to find, it has taken me over 30 years to determine that.

Environmental illness as the result of toxic effects of environmental pollution accumulation in the body. The buildup of toxins due to several different environmental contaminants, pesticides, industrial chemicals compromises the entire immune system, endocrine system and leaves the door wide open for other pathogens to enter the body, like bacterial, viral, fugal, protozoa infections, parasites, filariasis, etc.,

Which came first is the key to addressing the whole systemic system. It has become so obvious to me in the last 10 years that Hypothyroidism is far more common and not suspected in horses and the vast majority of horses that come to me for treatment for chronic stealth infections, do indeed have some form of thyroid dysfunction. It is undoubtable that mild to severe hypothyroidism is a modern epidemic.

Failure of Testing:

I always question why so many racehorses in particular,  that I have seen that never succeeded not reach their full potential due to hypothyroidism, those of which all had serum thyroid hormone tests come back normal, question is why did testing fail them.

Dr Barnes MD, Phd., was a famous thyroid researcher of 50 years who conducted thousands of studies of basal metabolism studies. Barnes didn’t consider his Basal Temperature Test to be 100% conclusive, and acknowledged there were other causes of lowered basal temperature. Nevertheless, he maintained that it was the most useful diagnostic test in the diagnosis of hypothyroidism, superior even to all modern blood tests. Barnes considered modern blood tests–like the Basal Metabolism Test and the Protein Bound Iodine Test to be unreliable, leaving many patients with clinical symptoms of hypothyroidism undiagnosed and untreated. Barnes estimated in the 1980’s, that the prevalence of undiagnosed hypothyroidism had risen to affect more than 40% of the American population.he discovered that the best method of diagnosing hypothyroidism was through temperature tests, which still today remains the most accurate method.

Effective Diagnostic Measures

This most effective method of diagnosing hypothyroid in horses is to take daily rectal temperatures, on a regular basis, along with presenting symptoms (From list attached) is very important and such a simple method, even for lay people to perform themselves. It has become evident to me in recent years and this is revolutionary in helping horse who struggle, with constant health issues, that could be so simple as that of thyroid gland dysfunction.

Once the horses undergo treatment for presenting symptoms and the underlying thyroid dysfunction is addressed we have seen profound positive and lasting changes in horses who undergo the treatment.

Taking daily basal temperatures along with the symptoms I have listed here in this article is the most efficient diagnostic measure. If temperatures are below 99.6* F, 37.5* C for 5 consecutive days then it is advisable to take some action.

In TCM (Traditional Chinese medicine) Hypothyroid is generally a Yang Deficiency, Interior cold. Yang deficiency especially of the Spleen and kidney is also very common these days in all species, especially in younger individuals, which was unheard of years ago all attributed to environmental contaminants.

Thyroid Function

After reading some work done by Dr Broda Barnes, MD Ph.D is impossible to overemphasise the importance of the thyroid, a small gland located in the neck. It is the thyroid that controls metabolism – the process in which food is transformed into energy and many chemical changes take place. Minute thyroid secretions, that are responsible for much of the body’s heat production. They help maintain the circulatory system and blood volume. They are necessary for muscle health. They heighten sensitivity of nerves. Every organ, every tissue, every cell is affected by the hormone secretions of the gland. That severe hypothyroidism can have devastating effects has long been appreciated, which is a rare occurrence, but mild or moderate hypothyroidism is far from rare.

It is the thyroid gland, lying in front of the throat, which regulates the rate at which the body utilises oxygen and controls the rate at which various organs function and the speed with which the body utilises food. In a way, the thyroid, through its hormone secretions, functions as a kind of thermostat. Each individual cell in the body is much like a microscopic power plant. it burns food and sets energy free, some of the energy being released as heat.

Thyroid secretion is essential for the operation of the cell and, in effect, determines how hot the fire gets in the cell and the speed of activity in the cell. The term “metabolism” refers to the fires within body cells. The influence of thyroid secretion on body processes and other organs is almost incredibly widespread and important.

When the thyroid gland is removed from an otherwise normal animal, all metabolic activity is reduced. A decrease in heat production begins–in rabbits, for example, within five to seven days after the operation. By about the third week, metabolism reaches its lowest level, 35 to 40 percent below normal, a reduction corresponding to that seen in severe cases of hypothyroidism in humans. The metabolic rate may be restored to normal or even to above normal by the administration of thyroid substance. After removal of the thyroid gland, excess amounts of water, salts, and protein are retained within the body. Blood cholesterol also goes up.

The thyroid plays an important role in growth processes. Tadpoles, deprived of thyroid, failed  to metamorphose into frogs, but they do so at an accelerated rate when excess thyroid is administered. If a just hatched tadpole is given extra thyroid hormone, it turns prematurely into an adult frog about the size of a fly.

In the human, growth and maturation fail to take place normally when the thyroid is absent or functioning far below normal. Children lacking on normal thyroid function may remain small; their stature can be improved considerably by thyroid medication started at an early age.

Ray Pete Ph.D. in Biology from the University of Oregon:

Many children approaching puberty, as estrogen is increasing and interfering with thyroid function, have “growing pains,” in which muscles become tense and sore after prolonged activity. When hypothyroidism is severe, it can cause myopathy, in which the painful swollen condition involves the leakage of muscle proteins (especially myoglobin) into the blood stream, allowing it to be diagnosed by a blood test. The combination of hypothyroidism with fatigue and stress can lead to the breakdown and death of muscle cells, rhabdomyolysis. This is indeed a very common issues in horses.


Another feature of fatigue (and often of aging, stress, and sickness) is that the relaxation of muscles is retarded and impaired.

Hypothyroidism causes muscle relaxation to be slowed, both in skeletal muscles and in the heart.

F/Z. Meerson showed that stress causes heart muscles to be exposed to increased calcium, followed by breakdown of fats and proteins, and that these changes keep the injured heart in a continuous state of partial contraction, making it stiff, and resistant to complete contractile shortening. When many cardiologists talk about the heart’s stiffness, they are thinking of muscular thickening and fibrosis, but those are late consequences of the kind of contractile, unrelaxed stiffness that Meerson described.

The hypothyroid heart does eventually become fibrotic, but before that, it is just unable to relax properly, and unable to contract fully. This failure to empty fully with each contraction is a kind of “heart failure,” but it can be corrected very quickly by supplementing thyroid. Even the fibrotic heart can recover under the influence of adequate thyroid.

Hypothyroidism tends to cause loss of sodium from the blood, and the hyponatremia sometimes leads to a generalized hypotonicity of the body fluids. The thyroid hormone itself functions as an antioxidant, but much of its protective effect against cell damage is probably the result of preventing cell swelling and accelerating the removal of calcium from the cell. (Swelling, like fatigue, causes intracellular calcium to increase.)

One of the oldest tests for hypothyroidism was the Achilles tendon reflex test, in which the rate of relaxation of the calf muscle corresponded to thyroid function–the relaxation is slow in hypothyroid people.

Water, sodium and calcium are more slowly expelled by the hypothyroid muscle. Exactly the same slow relaxation occurs in the hypothyroid heart muscle, contributing to congestive heart failure, because the semi-contracted heart can’t receive as much blood as the normally relaxed heart. The hypothyroid blood vessels are unable to relax properly, contributing to hypertension. Hypothyroid nerves don’t easily return to their energized relaxed state, leading to insomnia, paresthesias, movement disorders, and nerves that are swollen and very susceptible to pressure damage.


With aging, hypothyroidism, stress, and fatigue, the amount of estrogen in the body typically rises. Estrogen is catabolic for muscle, and causes systemic edema, and nerve excitation. It weakens muscle contraction in the bladder, although it lowers the threshold for stimulation of sensation and contraction (Dambros, et al., 2004).

This is the pattern that causes people to wake up frequently, to pass a small amount of urine. (Progesterone has the opposite effect in the urinary bladder, raising the threshold of response, but strengthening contraction, as it does in the gallbladder.) Estrogen lowers stimulation threshold in the gallbladder, as it does in the brain. Part of its excitatory action might be the result of increased hypotonic tissue water, but its effects on nerve thresholds are practically instantaneous.

Lactic acid production increases with fatigue, aging, hypothyroidism, estrogen excess, and other inefficient biological states. Its presence, when oxygen is available, indicates that something is interfering with efficient oxidative energy metabolism. Ammonia, free fatty acids, and various inflammatory cytokines are also likely to increase in those stress states.

Environmental Contaminants Affecting Thyroid function.

  • Radiation exposure both from nuclear fallout and medical radiation.
  • Water Contaminates- Fluoride can cause hypothyroidism, worth getting a good filtration system in place for drinking water.
  • Commercial fertilisers, high iron and manganese
  • Heavy metals like that of arsenic, cadmium, lead, mercury etc.,
  • Soy products-contain three potent estrogenic substances (plant or phytoestrogens), which inhibit thyroid function an the conversion of T4, the inactive form of the thyroid hormone to T3, the inactive form of the thyroid hormone.
  • Polyunsaturated Fats (PUFA or omega-3 and -6 oils) This includes all oils liquid at room temperature including: Soybean, canola, safflower, corn, flaxseed, fish, evening primrose, and borage oils. The use of polyunsaturated vegetable oils, whether processed or not, interfere with the thyroid receptors. (Dr Ray Peat Townsend Newsletter, April 1994))
  • All forms of Estrogen: whether natural, synthetic, herbal or environmental are toxic.
  • Pesticides used in the growing of animal feed:

Pesticides are estrogenic substances which inhibit the function of the thyroid. Pesticides used in agriculture to protect crops from pests, weeds, and disease. One such pesticide is glyphosate, the active ingredient in RoundUp.

Symptoms associated with Hypothyroidism:

Patients can suffer from a wide variety of symptoms and no two horses may present with the same symptoms

  • Low Basal temperatures-99.6* F or under
  • Fatigued/Chronic Fatigue
  • Anemia
  • Poor hair growth, thin manes, tail.
  • Thin or Obese
  • Irritability/Anxiety
  • Irritable Bowel Syndrome
  • Tongue Enlargement (Tongue Tie necessary in race horses) DDSP
  • Laryngeal Paralysis-Roaring
  • Choke
  • Laboured or difficult breathing
  • Heat Intolerance
  • Over sensitive to cold weather
  • Poor quality hoof growth, brittle hoofs, toe cracks.
  • Poor blood circulation to the feet (Microcirculation issues)
  • Cold feet
  • Restless leg syndrome/tremors, cramps.
  • Anhidrosis – decreased sweating
  • Prone to infection, particularly respiratory, but not limited to them.
  • Allergies
  • Arthritis
  • Skin Issues, dry flaky skin, eczema, fungal infections.
  • Glaucoma
  • Irregular oestrus cycle in mares,  Ovary syndrome, Infertility in stallions
  • Progesterone deficiency
  • Tying Up, Rhabdomyolysis
  • Poor Performance- eg.,race horses who don’t train on, or finish out their races.
  • Metabolic Syndrome (EMS)
  • Cushing’s Syndrome
  • PSSM
  • EPM- Equine Protozoal Myeloencephalitis
  • Shivers

Low thyroid can result in high adrenal/cortisol and can produce states of irritability, depression lack of sleep can cause a lot of other health issues. If you can get your cortisol and adrenal under control

By addressing the thyroid, these symptoms would normalise. A lot of horses are hyperactive or even those that are lethargic and fatigue easily, all have thyroid dysfunction.

For further advice on how to approach this problem and effective treatment protocols, please email me to arrange a consultation.