August 21, 2023
On: Sweet White Clover, Cattle Disease, Molds, Coumarin and Warfarin, and its threat to owls.
Sweet White Clover (Melilotus albus) is a white-flowered weed plant I observed along my regular walking path. This species is presently in bloom and very common along pathways, fields, and waste places. Sweet White Clover is a member of the legume, Fabaceae or Pea Family…and is closely related to the common white and red clover of lawns, parkland grass areas and playgrounds. Sweet White Clover produces flowers in a long, terminal raceme or spike, rather than the compact ball of the common white clover. Its leaves which have a blue green cast, occur in a three-leaf pattern, like the common clover. When crushed, the leaves give off a sweet, some say, vanilla-like fragrance. This plant is a native of Europe and Asia. It can grow to a height of 3 to 5 or more feet in fields, and is a common element in grasses cut for cattle forage and dried for use in winter (hay). It is often found as a component in bales of hay. When dry the sweet vanilla like aroma is more pronounced. As a member of the pea family, it produces its own nitrogen from nodules on its roots. Sweet White Clover is a very nutritious element in cattle forage or silage. This author has often encountered it as a welcomed and fragrant element in our local hay. On about this date, the author counted 51 plants along a one meter wide, kilometer long strip of walking path grass border. So look for it on your next walk in the outdoors.
But besides its pleasant appearance and fragrance it has had a fascinating history and great importance to medicine and human activities.
Like very many wild “weed” plants, Sweet White Clover has many, not so-well-known, useful properties. Wild herbs and weeds were used in ancient Egypt where medicinal plants and their uses were recorded on temple walls as long ago as 1500BC. In about 350BC Aristotle compiled a long list of useful medicinal plants. These herbs and weed decoctions of untold weed species have been in use ever since.
Aspirin was discovered and purified from concoctions herbalists prepared from the bark of the common willow tree (Salix sp). This wild medication was used as a febrifuge or fever reducer and pain reliever. Penicillin, the medically life-changing historic drug was discovered in 1928 when the common blue-green Penicillium mold was accidentally introduced into a bacterial colony of a disease organism (Staphylococcus aureus). The wild mold prevented the growth of the infectious bacteria and was soon adapted as one of the most significant medical discoveries in human history.
Why are these useful or life saving drugs and chemicals so often found in common wild plants? The answer is: evolution and time. Plants have had nearly a half a billion years of time on Earth to evolve chemical solutions to threats to their survival.
The first terrestrial vascular plants, appear way back in the Silurian Period of the Paleozoic Era or about 440 million years ago (mya) when simple moss-like plants first inhabited a warm, supercontinent called Gondwana.
Plants are sessile and almost always stationary. They can not escape from predators, insect attacks, disease or competitors. Thus, to survive, they had to turn to internal chemistry for a protective response. Over the hundreds of millions of years, they evolved many chemical responses for their survival. The result has been a virtual “wild pharmaceutical compendium” of chemicals.
Plants not only evolved thorns, spiky leaves, but also bitter tasting chemicals to discourage, browsing or grazing animals. Desert plant species evolved wax to coat their leaves to decrease dehydration and excessive evaporation. Some plants such as Common Milkweed (Asclepias sp) evolved a sticky liquid-exudate as a response to boring insects. The sticky fluid served to slow the boring insect’s activities and eventually clog up the its spiracles or breathing pores. This substance, later known as latex was discovered and re-purposed for human needs. Other plants dealt with borers by producing a strong smelling deterrent. The Red Cedar tree (Juniperus virginiana) produces a reddish heartwood which exudes a fragrant “cedar oil” (insects use pheromones to navigate, breed and find food) cedar oil disrupts insects ability to use or detect pheromones. Boxes, closets and storage places lined with such wood deters insect depredations on clothing stored in such containers .
Back to our sweet-smelling Sweet White Clover that is so common today along our fence-rows and open fields.
In the Great Plains of the 1920s, herds of cattle suffered from a pernicious and deadly hemorrhagic (bleeding) disease. The affected cattle showed signs of stiffness and lethargy. During dehorning, other minor surgeries, or as the result of minor injuries and especially during parturition (birthing )these animals experienced uncontrollable bleeding, death often followed. Concerned cattle and livestock interests conducted feeding trials and chemical investigations of blood samples which finally led investigators to conclude that the cause of the hemorrhagic outbreak was components in the hay or silage consumed by the affected animals.
The common field weed, Sweet White Clover (Melilotus albus, and Yellow Sweet Clover M. officinalis ) were found as the cause. Both plants Sweet White Clover and its close relative, Sweet Yellow Clover are rich in coumarin. Coumarin is the aromatic agent which produces the sweet vanilla fragrance. In a bale of moldy hay coumarin can be converted (or molecularly fused) by common molds into dicoumarol. Dicoumarol is a very powerful anticoagulant and vitamin K antagonist which inhibits the availability of this vitamin and other blood coagulating elements in the animal’s blood. The result is uncontrolled bleeding in animals which have consumed moldy hay in which a significant amounts of M. alba, or M officinalis (yellow sweet clover)were included. Soon after this discovery farmers and ranchers were warned to carefully attend to insuring that hay was more fully dried. Fields with hay which included the useful and nutritious White Sweet Clover, were suspect. New tests became available to farmers to detect dicoumarol in hay.
By the 1950s scientists studying dicoumarol soon recognized that this chemical might be applied to other major farm problems…such as vermin control. Just as cattle die during parturition after ingesting dicoumarol, this chemical could cause fatal bleeding in rodents after ingesting baits laced with this chemical. Dicoumarol was soon recognized and modified to be useful as a potential and excellent rat poison.
A slightly altered form of of dicoumarol was synthesized by a Wisconsin lab, known as the “Wisconsin Alumni Research Foundation”. This group produced and sold the product using the letters of the organization: WARF, plus the suffix of “coumarin” (“arin”) added to the trade name: “Warfarin” is now one of the most powerful and widely used rat poisons in history.
Furthermore, at much lower concentrations, the substance “warfarin sodium” was turned into a fabulously useful and popular human drug, adapted as a blood thinner and to dissolve blood clots. It was called “coumadin” to distinguish it from the rat poison.
In 1956, President Eisenhower, who had developed a life threatening blood clot, was successfully treated with this now famous chemical, all from the lowly, wild, introduced, invasive weed known as Sweet White Clover.
Sadly some of the rat poison applications of Warfarin…so widely used throughout the world— is taking a terrible toll on our nocturnal raptor birds. Owls are the most effective rat controlling bird. Barn Owls and Great Horned Owls kill and consume more than three rats per night and many more when they have nestlings. Many of these owls especially in urban and suburban areas kill and consume rats which have high concentrations of Warfarin in their bodies as a result of visits to our “oh so common” black plastic warfarin rat feeding stations.
A very well loved pair of nesting Great Horned Owls in our local area may have succumbed to just that threat: warfarin poisoning. The story of wild Sweet White Clover is not over. We need a better way to control rat populations. Perhaps more wild plant investigations will prove useful for this very serious problem.
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