For the Horse and Rider… Basal temperature, Thyroid, and Nutrition

Obesity is one of the many conditions associated with low metabolism and an improperly functioning thyroid.

By Kate Hester

Do you know your own basal temperature? Do you know your horse’s basal temperature? Do you know why you should know?


Energy is produced in a living body by oxidation and the burning of food chemically. Heat is produced as a byproduct of that burning. This heat in the body is basal temperature. It is an indicator of the amount of fuel burned, and also indicates the rate at which it is burned. Heat is necessary to speed biochemical reactions in the body. Basal temperature is the best indicator of basal metabolism, which is the rate at which biochemical reactions occur in the body without the added stimulus of exercise or eating.

The higher the basal temperature, the faster the metabolism. Most people are familiar with the idea that metabolism relates directly to body weight. A body with a slow metabolism has a tendency to be overweight; a body with a fast metabolism is generally trim. But how do basal temperatures and speed of metabolism relate to health in general?

Nature has designed an ideal basal temperature specific to each species, and for a very important reason - protection from disease. Each species has evolved its own unique temperature to best fuel its particular chemistry and enzymes. Each species, because of its unique metabolism, sources of food and niche in the ecological environment, has its own inborn weaknesses, or susceptibilities to different viral, bacterial and fungal invaders. The ideal basal temperature gives each species an adaptive advantage over its most commonly associated pathogens.


The human ideal basal temperature is 98.6 degrees F. Humans’ worst pathogenic threats are the strep and the yeast families, namely, Candida species. The yeast and strep can be grown in the lab at slightly lower temperatures than 98.6 but at this temperature growth is inhibited. So the ideal basal temperature for humans is approximately a degree to a degree and a half higher than the highest optimal temperature for threatening pathogens. As added protection, the body has the ability to pump up even more heat with a fever mechanism designed to “fry” infectious invaders. A basal temperature of less than 98.6 predisposes a body to chronic problems associated with overgrowth of yeast and strep.

The equine ideal basal temp is 100 to 100.8 degrees F, with geldings lower toward 100 and stallions and cycling mares at the higher end of the range. Horses and humans are similar, and our susceptibilities are similar as well. Both species are vulnerable to Candida and other yeast, fungus and strep. Strangles is a strep. The incidence of strangles (and incidentally, adverse reactions to strangles vaccinations) is on the rise. The typical strangles case is a horse with a lowered basal metabolism.

So, the basal temperature will tell whether a body is able to protect itself against its own worst pathogenic threats. If basal metabolism is good, then the body’s environment is inhospitable to these pathogens.


For the rider, this test is performed by the taking of oral temperatures first thing in the morning before rising from bed. Digital thermometers are not recommended for this because they generally are not completely accurate. These temperatures are recorded each day and, for women, are correlated to menstrual cycles. The temperature will dip the day before ovulation, then climb at ovulation and remain constant until the next cycle when it drops to basal levels again. The temperatures during the first part of the cycle reflect true basal levels, as temperatures during the last half of the cycle are elevated by progesterone.

For the horse, the basal temperature should be taken rectally every morning, also with a regular thermometer, before food or exercise is given. Fluctuations corresponding to heat cycles are normal for mares, as with women.

To have a reasonably accurate idea of true basal temperature, it is necessary to record temperatures daily. Slight variations in core body heat can result from environmental temperatures, seasonal changes, digestive processes, hormonal secretions, exercise, intake of food and water, and waste elimination. There are also diurnal variations, with higher temperatures during the day and slightly lower during the night.

Body temperatures are on the decline among the general population. While it used to be that a human temperature in the 96's range was rare, now 95's and even 94's are becoming more common. Lower temperatures are becoming more common in animals as well, relative to known normals for their species.

To understand why basal temperatures are lowering, it is necessary to understand the function of the thyroid, and to take a look at the various factors that are increasingly interfering with proper thyroid function in horse and rider, as well as all other living things on planet Earth.


In a healthy, properly functioning body, the thyroid, with help from the adrenal glands, regulates the speed of biochemical reactions in every cell of the body. This means that essentially all biochemical processes that go on in the body are regulated by these small glands in the neck. In other words, the thyroid is responsible for the basal metabolism, which can be monitored by recording basal temperatures.

The thyroid glands manufacture the hormone thyroxine, from the bonding of two molecules of the amino acid tyrosine, with four molecules of the mineral iodine. This molecule is called T4, because of the four iodine molecules and is commonly referred to as the storage form of thyroid hormone. The active form of the hormone that plugs into receptor sites of the cell membrane and "turns things on" is called T3. This form has had one iodine molecule removed by an enzyme process to free up a bonding site for the receptor.

When there is too little iodine (from the diet) at the cell level, a message is sent to the hypothalamus area of the brain to release more TSH, thyroid stimulating hormone, which in turn goes to the thyroid glands and stimulates the glands to produce more T4. The series of biochemical events (called pathways) involves more chemical transferals than are discussed here, but this is the basic chain of events, in a normal thyroid.

So, to function properly, a body needs sufficient quantities of the amino acid tyrosine and the mineral iodine. These are necessary ingredients for the manufacture of T4, from which the active form of thyroid hormone, T3, is made. If the T3 can properly plug into the hormone receptors at the cell level, all is well. However, many roadblocks can make these biochemical highways nearly impassable dirt roads.


Many of the conditions resulting from low basal metabolism - chronic depression, chronic fatigue, obesity - can be successfully treated in both horse and rider - if we also understand the other, interfering, mechanisms at work. Identifying these potential roadblocks in normal biochemical pathways involves using lab tests and symptomatology, but there are some for which we may not yet have developed a lab test. There is not yet a test for every compound, antibody or intermediary metabolite in the body. Relying exclusively on lab tests, without understanding and recognizing their limitations, can lead to treating and diagnosing the lab test results instead of the patient.

The first ingredient in the formula for thyroxine is the amino acid tyrosine. This amino acid is a neurotransmitter, which means that it is involved in carrying chemical messages within the brain. When basal metabolism is low and tyrosine is in short supply, the mental activity and thought processes are adversely affected. For every degree the basal temperature is below normal, a 13% decline in mental and physical energy and efficiency is experienced.

The manufacture of tyrosine in the body can be interrupted and nearly shut down by exposure to certain herbicides, which are commonly used in agriculture, and often abused in lawn care. In fact, homeowners are, by far, the most rampant users and abusers of herbicides in this country by not following directions in the dilution of these lawn care products. Thus tyrosine deficiency is a common roadblock.

Another common deficiency is iodine. In addition to possible dietary deficiencies of this mineral, iodine is subject to replacement in the body by environmental toxins. Any of the lighter and more chemically active members of the halogen family of elements (which includes iodine) - namely, fluorine, chlorine and bromine - can and will, if given half a chance, replace iodine in any and all chemical reactions. This means that these halogens are replacing the hormone molecules designed to fit into specifically designed receptor sites. This spells trouble for the thyroid and its pathways, especially since our environment is so polluted with chlorine, fluorine and bromine compounds.

You may have heard about some of these culprits of modern technology in DDT (an organochlorine) pesticide and PBB (a bromine fire retardant that was accidentally mixed into cattle feed in Michigan), and gases used in chemical warfare (also bromine compounds). Most of us experience everyday exposure to lower-weight halogens from bleaching of clothes, chlorinating water for drinking, languishing in heavily chlorinated and possibly brominated hot tubs and swimming pools, and brushing with fluoride laden toothpastes. The list goes on and on.

Exposure to any of these, or any other halogenated compounds, can interfere with our thyroid pathways, and even give false normal lab test results, as other halogen clouds (the electron outer orbital configuration common to all halogens, and responsible for their chemical natures), mistaken for iodine, are read by lab indicators. In other words, the other halogen molecules bond in the T3 and T4 molecules in the place of the iodine, and render the end product of the thyroid hormone invalid, yet are incorrectly identified by lab tests as normal thyroid production.

In addition to the halogens, there is another class of interfering toxic chemicals called dioxins. These are not commercial end products, but contaminants that are created during high temperature combustion by incinerators during the chlorine bleaching of pulp for paper and the manufacture of certain pesticides. A common point of contact with dioxins for humans is beverages contaminated by chlorine bleached paper products such as tea bags and paper coffee filters.

Recent research has shown that dioxin and thyroxine are chemical cousins, and that dioxin can plug itself into receptor sites meant for thyroid hormone and block the real thing, or worse, turn things off or to yet another function. To date, we are still learning about the family of dioxins, and they all appear to be bad apples. Dioxin was the contaminant in the now infamous Agent Orange herbicide of the Viet Nam era that still causes our veterans so much sickness today.

Environmental chemicals are very insidious, therefore, because they suppress the basal metabolism by interfering with the thyroid, and they inhibit the fever mode to some extent, so that our best defense against our most common pathogens is considerably lowered.


The current procedure for evaluating thyroid metabolism in the body is to first obtain a standard thyroid profile that measures circulating T3 (biologically active form) and T4 (storage form), plus a TSH (thyroid stimulating hormone). This profile, however, does not distinguish between the biologically correct molecules containing iodine and the incorrect molecules containing other halogens, and we often get inaccurate results.

Another problem, often exhibited among the hypothyroid (low thyroid levels) population, is the inability to enzymatically convert T4, the storage form of thyroid, to the biologically active form, T3, in any amount necessary to be truly effective. This common scenario results in the patient consistently showing "normal" T4 test results and still having the symptoms of low thyroid.

Simply relying on one test like TSH to gauge thyroid activity or dosage of thyroid replacement can miss a lot of pertinent information that could be implemented to make a dramatic difference in how horses and riders feel. If the thyroid had a normal ability to function in the first place, then it wouldn't be getting tested.


There are numerous symptoms that may be indicators of thyroid problems and many times people don’t recognize these symptoms as thyroid metabolism problems. Sometimes they don’t even know a problem exists if they are living in a state of non-disease rather than optimal health. It may be even more difficult to recognize a sub-optimal level of health in their horses.

To get to the bottom of what is going on when thyroid metabolism problems are suspected, one should first monitor and record the basal temperatures of the horse and/or rider daily. If temperatures are consistently below normal, consider increasing the protein intake as percentage of the total nutritional intake. Certain foods will fuel energy pathways in most people; that is, they will speed the metabolic processes. Likewise, there are foods that, for most people, will set up roadblocks in these energy pathways; in other words, they will slow down the metabolic processes. The logical conclusion is therefore, that attention to nutrition and diet can to some extent affect the rate of metabolism. Eating will always raise the metabolism, but while carbohydrates and fats raise it by about 10 percent, protein raises it by as much as 25 percent.

Since environmental chemicals make the basal chemistry of the body carbohydrate sensitive, it is also necessary to reduce high glycemic carbohydrates such as sugars and flour. If the basal temperatures increase to normal during these carbohydrate restrictions, the thyroid is probably functioning properly; if temperatures do not increase, then the thyroid is not functioning properly. If the basal temperatures do not increase after a week or two of higher protein intake, it is time to consider possible environmental disruptions to thyroid function. You may want to have thyroid function tested, but keep in mind that the test results will be in normal ranges whether the thyroid hormones or their mimics are bonded to the molecules. In other words, normal test results don’t necessarily mean things are working properly.

Be aware that thyroid supplementation should not be undertaken lightly. It is important to keep doses as small as possible to support normal metabolic processes. Once begun, thyroid supplementation is a lifelong commitment. A complete, natural desiccated thyroid is required as this is the only kind that will supply both T4 and T3.

Once we understand physiological responses to environmental contaminants, we can see that the body acts in a very logical way. Individuals can take steps to protect and eliminate these foreign substances from the body. The best remedy, however, would be to clean up the environment and eliminate exposure to environmental toxins. In the meantime, horse and rider can benefit from Vita Royal’s Nutritional Restructuring programs which promote the most efficient metabolism of the thyroid endocrine system and its metabolic pathways, while protecting the body from further damage from environmental toxins. To learn more about this, see

For more information:

Vita Royal Products, Inc.

4267 S. State Road

Davison, MI 48423

(810) 653-5478


About the author: Kate Hester is a freelance equine journalist and lives with several horses, including Chelan, and many other assorted wonderful animals at Lazy Dog Farm. Visit and for more photos of her horses' progress.

Please note that NHM invites and encourages questions related to this article, Environmental Illness, other health and nutritional concerns for horses and people, and Vita Royal Products in Ask Linsey, a regular column, following this article.