CURRENT USE OF HERBS IN EQUINE PRACTICE

Most herbs used today in the treatment of horses in the United States are selected by the client or recommended by another horse owner. Veterinarians are most often out of the picture. Consequently, the use of herbal therapy in the equine suffers from overuse and incorrect use. Owners may believe that if a little is good, a lot must be better. In addition, horses often have multiple problems, so a new formula is added to the feed for each new problem. The horse then may have 25 different herbs in the feed, and the client may wonder why treatment results are poor.

Most of those who call themselves equine herbalists are people with inadequate training, often not even professionally-qualified herbalists, who combine herbs but have no understanding of disease pathophysiology or equine medicine. This represents the biggest hurdle that must be overcome before herbs can be accepted into mainstream veterinary practice—many veterinarians recognize that herbal prescribing practices are of dubious quality and decide not to become involved with herbal medicine.

However, as more veterinarians become knowledgeable about herbs, the quality of herbal prescribing is improving. Ideal suppliers of herbal medicines use ethically harvested herbs and quality formulas prepared by educated herbalists. Many of these formulas can be safely and successfully used by veterinarians who have had basic herbal medicine training.

EQUINE ZOOPHARMACOGNOSY

The field of zoopharmacognosy is expanding, as the interest in herbs is growing (Engel, 2002). This is the study of how animals self-select plants and other materials such as minerals, possibly in order to address disease or discomfort. Animal behaviorists, ecologists, pharmacologists, anthropologists, geochemists, and parasitologists have all contributed to this truly multifaceted discipline (Biser, 1998; Buchanan, 2002).

Most owners have noticed that horses rarely eat the rich grass next to feces. Research has shown that many domestic species avoid parasites as they graze. For example, sheep avoided eating patches of vegetation with higher fecal burdens than were found in uncontaminated patches. Further study has shown that sheep avoid the consumption of grass infected with larvae, even though it may offer them higher intake rates (Hutchings, 1999). This is particularly the case for animals that are naive to parasites. Also, hungry animals are more likely to eat at the expense of larval ingestion. These studies appear to demonstrate that domestic animals might assess the costs, as well as the benefits, of their foraging decisions.

One study of ponies showed that they apparently are able to learn a taste aversion—although incompletely (Houpt, 1990). Illness was created with the use of apomorphine when the pony ate one type of feed (corn, alfalfa pellets, sweet feed, or a complete pellet) when other feeds were offered simultaneously. Ponies learned to avoid all feeds except the complete feed when apomorphine injection immediately followed consumption of the feed. However, they did not learn to avoid a feed when apomorphine was delayed for 30 minutes after feed consumption. They could learn to avoid alfalfa pellets, but not corn, when these feeds were presented with the familiar “safe foods”—oats and soybean meal. This study demonstrated that ponies have some ability to distinguish between safe and unsafe foods.

Few scientific observations of equine species have been reported. Most observations of horses apparently self selecting herbs have been made by traditional herbalists and indigenous people who pass their knowledge along to interested individuals. Many herbal formulas and individual herbs have been selected on the basis of these observations.

Consideration of the environment where wild horses live, both presently and in the past, suggests that little “grass” or green pasture is available. In fact, this author’s observations of wild horse environments have revealed that grass is scarce compared with the lush pastures of the civilized world. Even during the peak growing season, horses in native environments walk between every bite and are often surrounded by known toxic plants that they eat around. In winter, most natural environments offer little to eat at all; horses subsist on dried plant material of any sort that they can find.

Yet the modern horse owner assumes that horses require grass. When horses (that evolved to survive in relatively tough conditions) are placed in rich, lush, and fertilized fields without adequate exercise, they frequently become overweight and unfit. Other wild animals have been observed to become fat and unhealthy when they are given access to too much rich, unnatural food; it is easy to picture what would happen if the bears and monkeys in every national park were given access to junk food (Sapolsky, 1989).

Historically, it was recognized that “as regards to exercise, it is indispensable. No man or horse can ever enjoy good health unless habituated to daily exercise; it tends toward their health and strength, assists and promotes a free circulation of the blood, determines morbific matter to the various outlets, develops the muscular powers, creates a natural appetite, improves the wind, and finally invigorates the whole system” (Dadd, 1854). Medicine should not be given to prevent disease; “health is best preserved by the proper regulation of diet, exercise, and cleanliness” (Lawson, 1824). One of the fastest growing equine health problems is obesity and its associated illnesses.

Horses kept in fields will preferentially eat the grasses and legumes most of the time. However, horses grazing in a pasture in which a selection of plants is provided will eat a greater variety. At certain times of the year, for example, the tops of the yarrow in this author’s field are eaten. Whether these are eaten by horses or by deer has yet to be determined. When horses are removed from the field and are allowed to graze along the fence rows, yarrow is sometimes eaten and sometimes not. Dandelions are always eaten in the spring—but only occasionally at other times of the year. Most horses crave spring dandelions, and some will eat the dirt while trying to get at the roots, especially if they have been ill through the winter (Figure 21-1).

Figure 21-1 The Editor has observed horses in a training barn with access to rich pastures also eating chickweed, plantain, and privet bark. This thoroughbred was observed eating a bull thistle—note that the lip is elevated as if he is trying to avoid being stung by the spines. He ate thistle only for a limited time, then stopped.

Horses readily adapt to native and nonnative grasses, legumes, and plants in a given area. If horses are moved to a different part of the country, they generally can adapt to new forage. If the new forage is significantly richer in quantity or carbohydrate content than the forage on which they have been raised, the transition may be difficult or, at times, impossible. In many cases, horses must be removed from the rich pasture they were raised on and placed in dirt lots with very little forage to eat because they cannot handle the high carbohydrate content of rich grasses.

It would be interesting to study the behavior of horses in poor health when placed in a healthy, unfertilized pasture with a large selection of native grasses, herbs, and weeds. Detailed observations, including regular clinical examination, hematology and biochemistry should document any changes in health over time. It might then be possible to say whether horses actually self-medicate purposefully.

However, if domestic horses are raised in an artificial environment—exposed only to rich monoculture grass—it is possible that those horses will not instinctively know enough to self-medicate. Zoopharmacognosy researchers have tested the theory that animals learn which plants to eat by watching others of the same species (Huffman, 2001). Thus, a wild horse or a domesticated horse that has been raised with a natural, varied diet may be adept at determining which plants it should eat. These factors would need to be considered in research.

Author observation and information from toxicologists indicate that horses will not eat most toxic plants if they are well fed and do not graze in overcrowded pastures (Knight, 2001). Most poisonings occur when animals are exposed to unfamiliar plants, or when little safe plant material is available to graze. Certain plants such as red maple (Acer rubrum) and cherry (Prunus spp) become extremely toxic when the leaves are wilted. Domestic horses will often eat the wilted leaves; however, in most cases of poisoning, pasture overstocking has been found. Certain ornamental plants such as Yew may be unfamiliar enough to horses that they will eat them. Horses starved for green forage, as most confined horses are, will often eat indiscriminately anything green. Many “weeds” growing in barnyards are medicinal herbs or toxic plants; the vast majority of horses will never eat the toxic ones.

Ranching and grazing researchers have studied details about the grazing habits of livestock. Investigators examined which grasses were most palatable, and when they were most likely to be eaten (Fehmi, 2002). If given a choice of grasses to eat, cattle will select only what is at the peak of nutritive value and will leave the rest until it reaches peak. This indicates that cattle can make decisions about what is best to eat. Peak nutrition varies according to type of grass, season of the year, and climatic conditions. Research such as this does not show that animals are self-medicating, but rather that they recognize differences in the grasses they eat.

McClure wrote that horses should most often be fed hay if they are not being worked; corn and oats can be fed when they are working. Vetches and cut grass should be fed to horses that cannot graze in the spring. He believed that vetches and grass had cooling and refreshing qualities that were almost medicinal in effect (McClure, 1917).

Most modern horses have no idea what a day’s work is; many are ridden less than an hour at a time and only a few days a week. They are fed large quantities of processed grain while they stand in a small stall or pen. In nature, horses walk about 20 hours a day and sleep less than 4 hours (Pascoe, 2000). Many modern stabled horses are almost never fed fresh greens—a fact that has increased the incidence of vitamin E deficiency diseases such as equine motor neuron disease, as well as fertility problems (Divers, 2003).

DRUG TESTING AND HERBS

Equine veterinarians working with competition horses may be asked whether a specific herb or formula will cause a positive drug test. Practitioners are responsible for any positive tests if they prescribe or approve an herb, and they should be cautious. No set answer exists regarding which herbs are legal because new tests are devised regularly. Any list published here or on any Web site should be considered partial. Positive test results are possible with herbs, so practitioners should consult with manufacturing companies and drug testing laboratories for advice. If there is any question, it is better to withdraw the herb rather than risk a positive drug test.

Herbs fed in extract or tincture form may contain higher levels of forbidden compounds because of the increased concentrations. However, other compounds may actually be present in lower quantities because some compounds are not soluble in alcohol or glycerin. Currently, no data are available on the concentrations of forbidden compounds in extracts versus raw herbs, so caution must be used if extracts are used regardless of whether the raw herb sources are forbidden.

Herbs that contain salicylates such as white willow bark (Salix alba) and others that can be sold under the name of white willow—crack willow (Salix fragilis), purple willow (Salix purpurea), and violet willow (Salix daphnoides), along with meadowsweet (Filipendula ulmaria) Betula (birch) spp, Populus (poplar) spp, and bilberry (Vaccinium myrtillus)—have strong potential for producing a positive drug test. Salicylic acid is illegal in competition. Metabolism of plant-based salicylic acid precursors has not been studied in horses; however in humans these compounds undergo hepatic conversion into salicylic acid. It is unknown whether the concentration of salicylic acid precursors in these herbs are great enough to create a positive test. Willow bark and meadowsweet are the only herbs containing salicylates that are specifically listed as forbidden (United States Equine Federation, 2005).

The herb valerian is specifically singled out as an illegal compound in competition, with a 7-day recommended withdrawal time. Many horses do receive large quantities of valerian at shows, and a few positive tests have apparently been recorded. This herb should not be included in competition horses’ formulas. Other herbs that have quieting effects have been used without reported positive tests; however, their use is not without risk as new tests are being developed regularly.

Essential oils and herbs with strong odors or mixed with ingredients such as peppermint (Mentha piperita), camphor (Cinnamomum camphora), menthol (Mentha spp), rosemary (Rosmarinus officinalis), and thymol (Thymus vulgaris)—typically used externally—may produce a positive test result if the horse ingests the compound through licking. These compounds are often considered masking agents for other illegal drugs, so they themselves are listed as illegal.

The guidelines that are available for compounds that may cause a positive drug test state, “Any product is forbidden if it contains an ingredient that is a forbidden substance, or is a drug which might affect the performance of a horse and/or pony as a stimulant, depressant, tranquilizer, local anesthetic, psychotropic (mood and/or behavior altering) substance, or might interfere with drug testing procedures (USEF, 2005).” These regulations also provide “… just some of the examples of the hundreds and perhaps thousands of examples of herbal/natural or plant ingredients that would cause a product to be classified as forbidden …,” indicating that in the future, possible testing may be available for any herb. Herbs specifically listed as prohibited in the United States are included in Table 21-1. In Australia, listed prohibited herbs include white willow, kola, kava, guarana, and valerian, but other herbs may be tested for. Chinese herbs with known compounds that can test positive are listed in Table 21-2 (Xie, 2003). Other Chinese herbs may consist of similar compounds but are not specifically listed as prohibited.

TABLE 21-1 Herbs Specifically Prohibited in Competition in the United States

TABLE 21-2 Chinese Herbs That May Be Forbidden in the Racing Community in the United States

From Xie, 2003.

QUALITY CONTROL ISSUES

Because of the large volume of herbs needed to treat even one horse, the temptation may be great for a company to use less-than-ethically harvested herbs. Herb quality and manufacture is as important today as it was in the past. Even in 1843, Youatt warned herbalists to stay away from powdered ginger because it was usually adulterated with bean meal or sawdust, then was made warm and pungent with capsicum; he recommended purchasing the whole root and grinding it (Youatt, 1843). To this day, the natural products industry is largely unregulated, and many poor-quality products are sold (Butters, 2003). A company without much knowledge of herbs can easily purchase poor-quality products without even being aware of it. The reader is referred to Chapter 17 on sustainable harvesting and endangered species, as this is another very important issue.

Well-informed clinicians should investigate the companies they intend to use by asking questions about purity, sources of ingredients, and independent testing practices. A formula is only as good as the formulator, so the clinician should learn the credentials behind product developers. Formulators, whether veterinarians or nonveterinarian herbalists, should have had extensive education in botanical medicine, as well as equine experience. Clients who choose to use herbal preparations on their own initiative should be counseled about the advisability of obtaining products from reputable companies with a strong dedication to research, quality control, and ethical harvesting.

In the United States, practitioners who must find out which companies are committed to quality control should contact the National Animal Supplement Council (National Animal Supplement Council, 2005). This is an alliance of companies dedicated to quality control and self-regulation and opposed to unnecessary government regulation. These companies work to raise the standards within an industry that often profits from the use of poor-quality raw materials. No such industry alliances have yet been formed in other parts of the world, to this author’s knowledge.

ADVERSE REACTIONS

An adverse or toxic reaction to a substance occurs when an unfavorable, harmful, destructive, or deadly outcome occurs (Brown, 2001). An adverse or toxic reaction is one that is known to occur with the administration of a particular substance, for example, diarrhea after the administration of aloe. An idiosyncratic reaction is one that occurs when a compound that is routinely safely administered causes unique symptoms in one individual, for example, hives after the administration of meadowsweet.

Because no database is available widely to document adverse events related to herbal medicine in the equine, it may be impossible for a practitioner to know whether an herb is responsible or some unique reaction has occurred. VBMA (Veterinary Botanical Medicine Association) has the facility to record reported cases and is available at www.vbma.org. Consultation with an experienced equine herbalist may be helpful. In all cases, when any adverse event occurs, possible contributing factors such as concomitant drugs, diet and doses should be recorded. The product should be discontinued immediately. If the clinical sign subsides rapidly and was mild when it occurred, the product may be administered again at a lower dose after a week; if the sign then recurs, the product should be discontinued completely.

In the author’s experience, most good-quality herbal preparations used judiciously have proved to be relatively safe. However, compromised health status (e.g., impaired liver or kidney function) may alter response to such products. It must be remembered that any animal can have an idiosyncratic reaction to any substance—even if the compound has a long history of safe use.

The veterinarian should also remember that many people do not view herbal preparations as substances that need to be mentioned to the veterinarian. Many do not appreciate that herbs have the potential to alter a horse’s response to a drug, or that the potential for serious adverse events exists.

The reader should remember the proverb, “the dose makes the poison.” Several reasons can be proposed for an adverse event associated with an herbal preparation:

CAUTIONS WITH HERBS

PREGNANCY

A number of herbs are contraindicated in pregnancy because (1) they have the potential to cause uterine contractions, such as black cohosh (Cimicifuga racemosa), (2) they may alter hormones in a manner that can result in risk to the pregnancy, such as fenugreek (Trigonella foenum-graecum) (Gruenwald, 2000; Blumenthal, 2000; Brinker, 2000), or (3) they are teratogenic, such as comfrey (Symphytum officinale) (Gruenwald, 2000; Brinker, 2000) (Table 21-3). Because no specific research has been undertaken to investigate the equine, it is best for the practitioner to assume that an herb that is specifically contraindicated for use in pregnancy in humans or other species because of known biochemistry should not be used in the equine.

TABLE 21-3 Some Common Herbs Contraindicated in Pregnancy

* This is not a complete listing of all herbs known to have effects on pregnancy, but it includes most of the ones commonly used in equine practice.

HERB/DRUG INTERACTIONS

At the present time, very little, if any, research has been conducted in the equine concerning herb/drug interactions and adverse reactions. However, it is possible and desirable for the practitioner to examine the data collected for other species and to at least consider that they may be applicable to the horse (Brinker, 2001; Harman, 2002). This is especially true for herb/drug interactions because the drugs used in horses have similar biochemical effects in other species. Some of the adverse reactions seen in other species may not occur in the equine because the digestive tract is designed to handle a large variety of plant material.

PRACTICAL USES OF HERBS

Horses are herbivores and as such are designed to eat unprocessed herbs (fresh or dried). The horse’s cecum breaks down plant fiber very effectively. No studies show the digestibility of dried herbs in horses versus tinctures or extracts. In this author’s experience, all forms work well. However, if an extract or tincture is very concentrated and was made from many more pounds of herbs than would normally be fed, the extract appears to act more rapidly.

Horses can be fed herbs in the whole, unprocessed state or as powders. For roots, powders are best because whole roots may be too hard to chew properly—even for the horse. Alcohol extracts are expensive but easy to give mixed in with food; however, some horses may not like the alcohol taste. If alcohol tincture is administered directly into the mouth, horses that dislike the taste will become very difficult to dose. It is better to dilute with some water, vinegar, or other liquid to offset the alcohol, or to use glycerin extracts.

Horses lend themselves well to topical applications of herbs—especially on their legs, which are highly prone to injury. Ointments, salves, liniments, gels, washes, paints, sweats, and poultices all can be applied under a bandage or with no bandage. Topical herbs are usually well tolerated by most horses, but some are sensitive to any medication. If irritation, scurf, or peeling of the skin is seen, one should remove the bandage, decrease the frequency of application (to every other day or once a week), or discontinue use.

Horses are more sensitive to, and require smaller quantities of, many food and drug items per pound of body weight than are small animals with a higher metabolic rate. This is true of many larger species of animals. Dosing in modern times has been based on experience and extrapolation from the old texts. However, doses derived according to McClure in 1917 were also empirical and approximate and were determined without a specific reason—they were just what had been found to work (McClure, 1917).

It is interesting to hear the experiences of Dr. Huisheng Xie (personal communication), the noted Chinese herbalist, after he came to the United States. In China, veterinarians received the lowest-grade herbs for use with animals, while the high-quality herbs were sent to export and to human hospitals. In the United States, only high-quality human-grade herbs are used (those that were exported), in his experience, and the doses required to get results dropped dramatically, to a level that is only a few times higher than the human dose.

Personal clinical experience has shown that a good rule of thumb for veterinarians to follow is to treat horses with two to four times the human dose of any given herb. Some modern herbal literature often uses a “handful” of leafy herbs as one dose (deBairacli-Levy, 1976; Ferguson, 2002; Self, 1996). Measured a bit more exactly, this dose is approximately 30 grams or 1 ounce (Self, 1996).

Doses are usually administered twice a day at feeding time. More frequent dosing might produce a faster response, especially in acute situations. In most cases, compliance will go down significantly if owners are asked to dose too frequently. Most formulas are designed to be fed for several months, although in acute cases or with the use of more toxic herbs, treatment times may be shorter. Horses should be introduced to herbs slowly if they are at all suspicious of the additions to the feed.

A number of older methods of dosing are not used much today but certainly have potential. Dadd usually made mixtures of herbs in a liquid drench with something to make it palatable, such as caraway seeds or honey. McClure used flax oil, spirits of turpentine, warm ale, or aloes in a solution. He would fill an old champagne bottle and tip it up, giving the solution slowly without any force, to allow time for the horse to swallow. Perhaps in modern times, a plastic bottle could more safely be used. Dadd definitely had a gentle approach to the horse compared with others of his time.

Another common way to administer herbs at the turn of the last century was with the use of a ball, sometimes called a “Physic ball”. The ball was made with powdered herbs, linseed meal, treacle (pale cane syrup) or honey, and a bit of palm oil. These ingredients were mixed into a ball, with some being fairly hard, others slightly soft. Dadd believed this was bulky and difficult to give, that it required force to pull the tongue out and shove the bolus down the throat, and that it was slow to dissolve and deliver the active compound. Lawson and Clater used balls, frequently mixing in licorice powder to improve the consistency (Lawson, 1824; Clater, 1817).

FORMULA SELECTION

The selection of a formula should be based on a complete history and physical examination, as should any prescription. A complete health history covering the entire life of the horse is beneficial. However, it must be noted that many horses have been owned by the current caretaker for only 2 to 4 years, so information on past history may be difficult to obtain.

For instance, a horse with summer skin eruptions may have been purchased in winter and may have no history of previous skin disease. Horse trading has never been totally honest, so one does not know whether the previous owner is ignorant of, or lying about, skin problems. Other horses have passed through several owners, and they may genuinely not know the past history. For example, a history of pneumonia as a foal may signal weakness in the immune system, and lead to fibrosis in the lungs, or the residual effects of a large quantity of drugs such as antibiotics that may affect long-term health.

If the practitioner has been trained to observe tongue color and feel pulse, as is practiced in Chinese herbal medicine, that information can be added to the physical examination findings. McClure provided great detail about feeling the pulse on the angle of the jaw. He described pulse characteristics in various types of diseases. He accurately indicated how inflammatory diseases are associated with increases in pulse strength and rate, and how debility was associated with decreased pulse strength. He also recognized that sometimes the pulse was quicker in animals with debilitating disease. Although he offered no explanation for this variation of the pulse in debility, an understanding of Chinese medicine would suggest that he is describing a Yin deficiency.

Lawson, a practitioner who was active in the early 1800s, described in detail pulses felt at the jaw line (Lawson, 1824). The normal pulse felt perfectly elastic, neither hard nor soft, but in fever, it was increased. With fever, the pulse felt hard and rigid, and it resisted pressure from the fingers. He recommended bleeding until the pulse felt softer. The Chinese also used bleeding techniques when monitoring results by checking the pulse. Although this text does not discuss Chinese medicine, it is interesting to note that some early herbalists in this country used the same type of information (Table 21-4).

TABLE 21-4 Traditional Chinese Veterinary Medicine Patterns

Once the diagnosis has been made, an individual herb or formula can be selected. Experienced herbalists can customize a single herb or a formula for individual cases. For many veterinarians, a prepared formula will be the preferred choice. The choice of which company’s formulas to use should depend on the quality of the company’s herbalist and the herbs themselves (see above, and Chapter 8 for more information). A formula can be selected on the basis of the clinical picture and fed for at least a month (about 2 weeks if the formula is in tincture form) before a reevaluation is undertaken to determine whether there has been a response.

PRESCRIBING CONSIDERATIONS

If a well-selected herb or formula is not working, it is important for the practitioner to reevaluate the case. Is the diagnosis correct? Is more information needed? Is the formula incorrect, or still appropriate after partial changes in the clinical condition have occurred? Is the horse consuming the full dose? Is the client paying attention to how much the horse is eating? Has the formula been given enough time to work? Is the horse under a heavy load of stress (showing, rough training, crowding in the pasture) which might be an obstacle to improvement? Is the horse’s digestive system fully functional?

One of the most likely reasons for a well-selected formula or herb not to work is that the digestive tract is functioning poorly. Horses are often fed large quantities of antibiotics for every cut, scrape, nasal discharge, and bug bite. They are also commonly fed extremely large quantities of nonsteroidal anti-inflammatory agents, the most common of which—phenylbutazone—leads to significantly increased permeability of the intestinal tract wall (McAllister, 1993). Antibiotics change the bacterial flora, so digestion may not be as complete as in a horse whose beneficial bacteria and protozoa are intact (Rolfe, 1984; Zinn, 1993). Because bacteria and protozoa are important for cellulose or plant wall digestion, an unhealthy digestive tract may not process herbs optimally.

How does one recognize a horse with an underfunctioning digestive tract? Signs can be subtle. A horse with a poorly functioning digestive tract often appears unthrifty, even though his teeth and deworming program may be adequate. The horse may or may not carry enough weight, but the coat does not have a deep, rich color to it. The manure may be abnormal—too soft, too hard, or not enough of it. An individual horse’s manure may be perfectly normal, yet the gastrointestinal tract may still be functioning suboptimally.

Many patients and herb formulas require 2 to 3 weeks before results become evident; it may take even longer for the full effects of treatment to be seen. If no response is seen at the end of 1 month, the practitioner should reevaluate the case, consider reformulation of the herbal therapy, or investigate the need for another form of therapy. If some positive response occurs, treatment should be continued for another month, at the end of which good response should be seen. If by the end of the second month, results are mediocre, critical reevaluation of the case should be undertaken.

FORMULAS FOR COMMON EQUINE CONDITIONS

In this section, treatments for some of the most common equine-specific conditions are presented from historical and modern perspectives. Conditions present in all species such as liver disease are discussed elsewhere in this text. Formulas can apply to the equine if the doses are adjusted. The number of commercial formulas available to treat equine disease is large and formulas given here are examples to build from, rather than to copy without thought. It would appear that herbalists at the turn of the century were as discouraged with much of the conventional medicine practiced then as herbalists are in the present time. Dadd and McClure were the main references for this section, unless otherwise noted (Dadd, 1854; McClure, 1917).

Sulphur is used in many old formulas. This mineral is currently deficient in many soils, and consequently, in horses as well. Horses readily eat sulphur when it is offered to them as a separate mineral, especially in the spring and fall as the coat changes. Sulphur is a key mineral that is required by the proteins common in hair and hooves. The herbalists of old times may have known something about mineral nutrition that should be incorporated into modern nutrition. Methylsulfonylmethane (MSM) (usual dose is 5-10 g/day) is a readily available source of sulphur. Elemental sulphur can also be obtained and salt blocks with sulphur can be offered, but the latter may be unpalatable for some horses if the salt level is too high.

Many of the herbs in common use today are different from those described in old veterinary texts and modern information on herbal medicine is more often available in the current human literature. Although this approach (applying similar principles) to equine herbal medicine is a valid one, much can be learned from hundreds of years of experience. Historical formulas can be adapted to modern times in many ways. One way is to substitute nontoxic herbs in formulas for those that are no longer available (e.g., opium [Papaver somniferum], aconite [Aconite spp]). It is not necessary for the herbalist to mix herbs in ale or even in treacle (syrup), as was formerly recommended, because sugar should be avoided or limited. Other types of ingredients may be omitted (e.g., carbonate of iron—iron deficiency is uncommon in the modern horse because it is plentiful in the diet). If iron supplementation is desired, blue-green algae and parsley are both high in iron. Experimentation over time with historical uses of herbs will expand the current Materia medica.