Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2003
Publication Date: 5/1/2003
Citation: HALAWEISH, F., KRONBERG, S.L., RICE, J.A. RODENT AND RUMINANT INGESTIVE RESPONSES TO FLAVONOIDS IN EUPHORBIA ESULA. JOURNAL OF CHEMICAL ECOLOGY. 2003. v. 29(5). p. 1073-1082. Interpretive Summary: The noxious weed leafy spurge, which was introduced into the Great Plains of North America from Europe, is a serious economic and ecological threat to the productivity of agricultural and natural areas. Cattle, the predominant livestock species on the Great Plains, as well as common wild ruminant species in this region appear to consume little if any leafy spurge. This is likely because they experience a toxic response after they consume small amounts of this plant and consequently learn to avoid it. There is little evidence that wild rodents eat the weed either. A variety of toxic compounds have been isolated from leafy spurge tissues, but compounds in this plant have not been evaluated in respect to their toxicity and capacity to cause ruminants and rodents to avoid consuming the plant (form feeding aversions to it). We conducted chemical fractionations of leafy spurge that were guided by biological assays with rats and cattle in an attempt to isolate toxic and aversive compounds in the plant. These bioassay-guided fractionations led to identification of two compounds called glucouronoides that were aversive to rats but not to cattle.
Technical Abstract: Euphorbia esula, common name leafy spurge, was chemically evaluated for aversive phytochemicals that appear to minimize herbivory by rodents and cattle. A portion of the initial aqueous methanol extract called the middle layer elicited food aversions in rats as did the petroleum ether extract of the initial methanol extract. Kaempferol 3-0-ß-glucouronoide and quercetin 3-0-ß-glucouronoide were separated and identified from the middle-layer residue. This study is the first report of quercetin 3-0-ß-glucouronoide in leafy spurge. Together these flavonoidal glucosides were mildly aversive to rats but showed less aversive activity when tested separately. The middle-layer residue produced no aversive response from cattle while the petroleum ether extract elicited strong aversions in cattle. Flavonoidal compounds from leafy spurge that were aversive to rats, a monogastric mammal, were not aversive to cattle, a ruminant. In respect to their interactions with these glucosides, microbial degradation of the compounds before they reach the intestines and are absorbed into the bloodstream is likely a key advantage for cattle compared to rats.