Treating Livestock with Medicinal Plants: Beneficial or Toxic?

Eucalyptus spp.

Index

Introduction

Eucalyptus spp. (Family Myrtaceae) originated in Australia. It now grows in almost all tropical and subtropical areas and is cultivated in many other climates. Much research has been conducted on the medicinal properties of Eucalyptus spp. Of the different species, E. globulus has been the most widely studied. Eucalyptus is used to treat many human ailments and some livestock ailments. Eucalyptus extracts, oils, or fresh leaves are used in steam inhalation treatments, consumed in teas, or used in bathing.

While Eucalyptus trees are well known for their medicinal properties and their strong fragrance, they are best known as the feed source for koala. The koala only eat a few species of Eucalyptus. However, there are over 500 species of the tree.

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Common Names


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Chemical Compounds

There are many compounds in Eucalyptus spp.. While the same compounds exist in many of the species, some compounds can be found in only one or a few species. Within species the quantity of essential oil and the specific compounds in the essential oil and extracts of dry and fresh leaves, buds, mature fruit, and bark vary with the origin of the tree and the age of the leaves. The following discussion and list of Eucalyptus spp. and the compounds in them is not comprehensive. The quantity of the compounds in the oils and plant parts are estimates based on several sources (listed in the references). For more information please refer to the references and the USDA Phytochemical and Ethnobotanical Databases.

E. globulusis one of the more important species of Eucalyptus. The essential oil in the leaves is commonly used for medicinal purposes. The quantity of essential oil ranges from less than 1.5 to over 3.5%. On average, between 70 and 95% of the oil is 1,8-cineole (eucalyptol). However, some studies have shown the oil to contain as little as 4% 1,8-cineole. The essential oil from the fruit, buds, and branches contain from 15-57% 1,8-cineole. Activities contributed to this compound include: anesthetic, antibronchitic, anticatarrh, antilaryngitic, antipharyngitic, antiseptic, antitussive, cns-stimulant, choleretic, counterirritant, dentifrice, expectorant, fungicide, hepatotonic, herbicide, hypotensive, pesticide, and sedative. Other major components in the oil are:

Other important compounds found in the leaves, buds, branches, and bark include:

E. citriodora essential oil contains mainly citronellol (approximately 58%), which is best known for its aromatic properties. Other compounds in the plant include:

E. camaldulensis essential oil (from the leaves) ranges from less than 1 to over 2%. The quantity of 1,8-cineole in the oil ranges from 15-78%. Other compounds in the leaves include:
Other Eucalyptus spp. of note and some of the compounds in them include:
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Toxicity

Eucalyptus spp. contain high levels of phenolics and terpenoids which can be toxic. Animals such as the koala which eat Eucalyptus have developed methods for detoxifying the compounds in the liver. In addition, they have bacteria that degrade tannin-protein complexes. Most animals do not have this ability.

Several adverse reactions have been attributed to the use of or contact with Eucalyptus oils, extracts, and fresh and processed plant material. Some of the specific compounds that can be toxic or cause adverse reactions include: 1,8-cineole, cyanogenic glycosides, rutin, and tannins. Most studies on adverse reactions have been conducted with rodents and most documented cases of adverse reactions focus on humans. Less information is available on livestock.

Overdoses of the oil in humans cause gastro-intestinal burning, abdominal pain, vomiting, and convulsions, depress respiration and the central nervous system, and may lead to comas and death. The data on deaths caused by consumption of eucalyptus oil in humans are not consistent -- death has occurred after consumption of as little as 4-5 ml, while other people have become ill and recovered after consuming 120-220 ml of the oil. Based on rodent studies, the oral LD50 (the orally consumed dose that is lethal to 50% of the animals) for eucalyptus oil is very high -- 4.44g/kg body weight(BW) for rats and 3.32g/kg BW for mice. The LD50 is lower when only 1,8-cineole is used -- 2.48g/kg BW for rats. The dermal LD50 for rabbits is greater than 5g/kg BW.

Eucalyptus oil is not believed to be teratogenic or contaminate milk. However, some studies have indicated that citronellal and phellandrene, which can be found in some Eucalyptus spp., are weak mutagenics and carcinogenics, respectively.

It is very difficult to determine the potential for adverse reactions with the use of Eucalyptus treatments. This is because, as previously stated, the type and quantity of compounds depends on the species (which often is not indicated on the label of purchased preparations), the age of the leaves, the method used for drying leaves, buds, and bark, and the preparation methods of essential oils and extracts. In addition, many studies on adverse reactions do not indicate the species or preparation method used, complicating the situation. While Eucalyptus spp. can cause adverse reactions, the U.S. Food and Drug Administration has approved the use of eucalyptus oil and 1,8-cineole (eucalyptol) for human food use. The Council of Europe also has approved the use of the oil as a human food additive (at a level of 15 ppm). In France, infusions of E. globulus leaves can be registered as products for the treatment human benign bronchial disorders without toxicological studies. However, some toxicological studies are required for the registration of powdered leaf formulas.

While not related to the use of Eucalyptus in treatments, I find it interesting that growing certain species of Eucalyptus can cause its own problems. In Australia sawfly larvae, which contain poisonous polypeptides, often gather in mounds beneath E. melanophloia. When cattle consume the larvae, they become uncoordinated, tremble, and can suffer permanent liver damage.
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Uses and Efficacy

As with toxicity, the efficacy of eucalyptus oils and extracts is most likely dependent on the their chemical composition. In general, oils from Eucalyptus spp. have antimicrobial properties. Two studies which tested the oils from several species showed that E. citriodora had the most antimicrobial activity. There was no relationship between 1,8-cineole content and antimicrobial activity. Other studies have demonstrated that the oil and leaf extracts of Eucalyptus spp. have antifungal and repellent activity.

The applications that are probably of most interest to livestock producers are as a mastitis preventative and treatment, as a treatment for endometritis, and as an anthelmintic (dewormer). An herbal gel called AV/AMP/14 (produced by Dabur Ayurvet Ltd. and contains Cedrus deodara, Curcuma longa, Glycyrrhiza glabra, and Eucalyptus globulus) was used to treat and prevent subclinical mastitis in crossbred cows. Twice daily topical applications to the udder significantly reduced somatic cell counts (Pavneesh et al. 1996 and Joshi et al. 1996).

In a study on bovine endometritis, cows with endometritis were given, via an intrauterine infusion, 100 mls of a 10% solution of a tincture (alcohol and water mixtures) of Eucalyptus globulus. The eucalyptus tincture was compared to tinctures of Allium sativum (garlic, believed to have antimicrobial activity) and Gnaphalium conoideum (a plant that has no antimicrobial properties). The parameters measured in the study included the number of infusions given (which were repeated every 48 h until there was a change in the endometritis) and the days to first visible oestrus, days open, and number of services before conception. All of these time periods are believed to be longer when there are infections in the reproductive tract. The eucalyptus and garlic tinctures significantly reduced the days to first visible oestrus and the days open, although fewer garlic treatments were needed. There were no significant differences between the three treatment in the number of services required for conception. The study did not included any approved, commercially available treatments for endometritis (Esparza-Borges and Ortiz-Marquez 1996).

Fresh leaves, leaf-extracts, and growth regulators and their intermediaries (which are endoperoxides) of Eucalyptus grandis were tested for their anthelmintic properties by Bennet-Jenkins and Bryant (1996). Leaves were fed to 5 goats with experimental infections of Haemonchus contortus (the barberpole worm) (and natural infections of Ostertagia) for seven days (two days with lucerne/oaten chaff and five days as the sole source of feed). At necropsy, the number of adult H. contortus in the E. grandis-fed goats was 91% lower than the number in 4 control goats. There was no significant difference in the number of Ostertagia. Isolated E. grandis compounds (and synthetic congeners) were affective in vitro and in vivo (in mice and sheep) -- but practical formulation and administration methods for these compounds have not been identified.

Another application that may be of interest to livestock producers is as a treatment for ectoparasites and non-specific skin infections. Two experimental herbal mixtures (AV/EPP/14 and AV/AAGD/14 produced by Dabur Ayurvet Limited in India), which contain Eucalyptus globulus oil along with several other plant oils, have been tested on dogs to treat ectoparasites, fungal skin infections, and non-specific skin infections. While the mixtures appear to be effective, no comparative treatments were used in the studies. Also, it is unknown which plant oils in the mixtures contain the most active ingredients -- that is, the eucalyptus oil may not have been the effective ingredient in the herbal mixture (Agrawal 1997 and Bhilegaonkar and Maske 1997).

Many in vitro and a few in vivo tests have been conducted with extracts and oils of different Ecualyptus species. Following is a summary of some of the specific activities identified for Eucalyptus spp.:

Listed below are some uses of E. globulus in humans:

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References

Not all of the references in the list below were used in writing this web page. Some references could not be easily located and others were in non-romance languages. They are included here so that a more complete resource list is available for those interested in the subject area.

This series of web pages was created by a graduate student at Cornell University. All comments and suggestions are welcome. If you would like to add to this medicinal plant database, please e-mail Webmaster.

WARNING These web pages are only meant to be informative. Neither Cornell University nor the author of this site endorse or recommend the use of these plants.

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