Location: Poisonous Plant Research2011 Annual Report
1a. Objectives (from AD-416)
Objective I: Determine Astragalus and Oxytropis species which contain fungal endophytes that produce swainsonine and describe the plant/endophyte relationship. 1.1 Identify species that contain the endophyte (Embellisia), determine transfer of the endophyte to successive generations, and determine if the endophyte increases fitness of locoweed plants. 1.2 Describe the distribution of the endophyte and swainsonine as a function of plant part and determine if swainsonine varies as a function of time. 1.3 Determine the effect of the endophyte on palatability of locoweeds. Objective II: Identify environmental conditions that will help predict population outbreaks of major locoweed species (Oxytropis sericea, Astragalus mollissimus, A. lentiginosus). Determine the conditions under which cattle, sheep, and horses graze locoweeds. 2.1 Relate locoweed population outbreaks to weather cycles. 2.2 Determine conditions under which livestock graze various locoweed species. 2.3 Determine influence of nitrogen supplements in livestock diet selection and locoweed poisoning. Objective III: Further describe effects of swainsonine and related polyhydroxy alkaloids on reproduction and body systems among livestock and wildlife species. 3.1 Conduct a comparative study of species differences to determine why mannosidases are inhibited differently. 3.2 Compare the effects of swainsonine on fetotoxicity among breeds of sheep and goats. 3.3 Compare effects of swainsonine on ovarian function among cattle, sheep, and goats. Objective IV: Characterize biomarkers of intoxication and develop better diagnostic and prognostic procedures. 4.1 Develop ELISA for locoweed intoxication. 4.2 Develop biomarkers of poisoning. Objective V: Further describe toxicoses and pathology of animals poisoned by Astragalus species containing nitro-propionic. Objective VI: Further describe the toxicosis, physiologic effects, and pathology of Astragalus and other selenium accumulating plants, and determine absorption, distribution, and elimination (clearance times) of various types and forms of selenium in livestock. 6.1 Describe the etiology and pathogenesis of selenium poisoning and deficiency in livestock and determine safe nutritional levels. 6.2 Determine the effect of selenium-reducing microflora on the selenium pharacokinetics when livestock consume seleniferous plant material.
1b. Approach (from AD-416)
1.1 Seed from “endophyte-free” and endophyte-infected locoweed plants will be germinated to determine if the endophyte is transmitted and expressed in the next generation. If so, we will develop endophyte-free and endophyte–infected populations and compare their fitness and competitive ability. 1.2 O. sericea plants will be collected and separated into plant parts and the endophyte measured by PCR. Once the endophyte distribution within the plant is known, we will collect stalks from independent plants at 2 week intervals throughout the growing season to determine endophyte distribution and swainsonine synthesis over time. 1.3 Fungal endophytes will be grown in the laboratory using standard culture techniques, then added to ground alfalfa hay, and presented to individual animals in preference tests. 2.1 Locoweed density will be measured annually in locations throughout the Western US, and correlated with weather data to develop predictive models. 2.2 A series of grazing studies will be conducted in northeastern New Mexico beginning in late summer while grass is green and run through early winter as grasses senesce to determine cattle preference for woolly locoweed. 2.3 Supplemented and nonsupplemented groups of cattle will be grazed to determine if the supplement will reduce locoweed consumption. 3.1 Tissues from several animal species will be analyzed and mannosidase expression compared using immunohistochemistry, Western blotting, real time (RT)-PCR and Northern blots. Enzymatic in vitro assays of mannosidase activity will be compared using a modification of previously developed serum a-mannosidase assays. 3.2 Swainsonine will be fed to hair sheep, wool sheep and goats in increasing doses. Swainsonine absorption and elimination profiles will be developed, fetotoxic effects will be monitored by ultrasound, and maternal histological comparisons will be evaluated. 3.3 Swainsonine will be fed to heifers, ewes, and goats at increasing doses. Ultrasound imaging will be used to evaluate changes in follicular phase and cyst development, histological changes in ovaries will be compared, and the biological activity of anterior pituitary gonadotropins will be assayed. 4.1 Swainsonine-protein conjugates will be synthesized and injected subcutaneously into four sheep and antisera titers determined. Antisera exhibiting high titers that are specific to swainsonine will be developed into ELISA’s. 4.2 Differences in blood proteome from animals poisoned by locoweed plants will be used to identify proteins that can be used as biomarkers, then they will be validated using actual locoweed intake data. 5. A dose response study in sheep and cattle will be conducted and tissues collected for microscopic, ultrastructural and chemical analysis. 6.1 Selenium from plant material will be compared to inorganic forms at increasing doses to determine bioavailability and toxicity in sheep. 6.2 Reproductively mature ewes will be inoculated with selenobacter (Wolinella succinogenes), fed gound seleniferous plant (Astragalus bisulcatus) for eight months to monitor the effects of chronic selenium dosing on estrus cycles, gestation, and initial growth of lambs.
3. Progress Report
Poisoning by Astragalus and Oxytropis species has been historically divided into three groups based on the toxic syndromes they cause in livestock: locoism caused by the toxin swainsonine, selenium poisoning, and nitrotoxin poisoning. Locoweeds contain the toxic alkaloid swainsonine. A fungal endophyte, Undifilum oxytropis, found in locoweed plant species was shown to be responsible for the synthesis of swainsonine. Two types of Oxytropis and Astragalus locoweeds were identified from field collections, plants that accumulate high concentrations of swainsonine and plants that accumulate low or non-detectable swainsonine concentrations. The plants with high swainsonine concentrations had relatively high amounts of endophyte while plants with low or non-detectable swainsonine concentrations had low or non-detectable endophyte amounts. The group of Oxytropis and Astragalus locoweeds containing low amounts of swainsonine can be inoculated with the endophyte resulting in a plant with high amounts of endophyte and swainsonine. These results suggest that the endophyte amount must reach some critical threshold before swainsonine is present at meaningful concentrations rather than some type of suppression of the endophyte. Furthermore, in plants colonized by the endophyte, their progeny inherit the endophyte and the ability to produce swainsonine. However, in plants where the endophyte has not effectively colonized the plant, endophyte colonization and the production of swainsonine are diminished significantly in their progeny. Additionally other plant species have been documented to contain swainsonine, including some Swainsona (Leguminosae) species in Australia and some Ipomoea (Convolvulaceae), Turbina (Convolvulaceae), and Sida (Malvaceae) species in South America and Africa. Fungal endophytes that produce swainsonine have been isolated from Swainsona canescens and Ipomoea carnea. Additionally, the toxicokinetics and pathology of steers poisoned by grazing forage contaminated with elevated selenium was investigated. Furthermore experiments have been initiated to investigate the effects of swainsonine on the concentration effect curves of agonists in cultured cells. Preliminary data suggests that swainsonine changes the concentration effect curves of a number of agonists.
1. Selenium toxicity in cattle. Although selenium is an essential mineral, livestock that eat poisonous selenium-accumulating plants can die. ARS researchers in Logan, UT, investigating acute selenium toxicity determined that 3% of yearling steers died after grazing rangelands infested with a selenium accumulating poisonous plant called western aster. Several steers were necropsied and severe damage to muscle tissue of the heart was associated with selenium toxicity. Additionally, some poisoned steers developed congestive heart failure weeks after the toxic exposure because the high levels of selenium are slowly eliminated requiring a relatively long period for selenium to clear from the animal’s system. Selenium elimination rates from animals provided useful information for food safety and for producers of animals grazing on forages high in selenium.
2. Swainsonine endophyte interaction in Astragalus and Oxytropis spp. Astragalus lentiginosus and Astragalus mollissimus are two major locoweed species in the southwestern United States causing significant losses. Swainsonine was detected in all parts of both these species with greater amounts found in the above ground parts. Likewise, the fungal endophyte, Undifilum oxytropis, responsible for the synthesis of swainsonine can be detected in both these species. Two chemotypes of plants were detected in population of both these species: those that contain swainsonine (> 0.1%; chemotype 1) and those that contain little or no detectable swainsonine (< 0.01%; chemotype 2). Chemotype 1 plants in both species had quantitatively higher amounts of endophyte compared to chemotype 2 plants. Understanding the relationship between swainsonine and the endophyte responsible for its production in natural plant populations may provide information to help render locoweeds non-toxic.
3. Survey of locoweed species in the Western United States. The locoweed endophyte is vertically transmitted to seed. Progeny resulting from parent plants that contained high amounts swainsonine and corresponding high amounts of endophyte inherited both high and low amounts of swainsonine and corresponding amounts of endophyte. Progeny resulting from parent plants containing low amounts of swainsonine and corresponding low amounts of endophyte inherited a similar profile of swainsonine and endophyte as the parent. Understanding how swainsonine and the endophyte responsible for its production are inherited may provide information to help render locoweeds non-toxic.
4. Locoweed poisoning in Spanish goats. Locoweeds (plant species of Astragalus and Oxytropis containing swainsonine) cause large economic losses to the livestock industry throughout the world from reproductive losses. ARS researchers in Logan, UT, fed locoweed to pregnant Spanish goats resulting in fetal death and abortions. Clinical signs including muscle tremors and aberrant behavior were also observed in the mother goat. It was concluded that similar reproductive and clinical signs that are observed in Spanish goats are also observed in other livestock. It should be noted that Spanish goats like horses are one of the more sensitive livestock species to locoweed poisoning with clinical signs and reproductive effects developing earlier. In summary, the research data suggests a rank order of sensitivity to be Spanish goats > horses > cattle > sheep.
Graham, D., Creamer, R., Cook, D., Stegelmeier, B.L., Welch, K.D., Pfister, J.A., Panter, K.E., Cibils, A., Ralphs, M.H., Encinias, M., Mc Daniel, K., Thompson, D., Gardner, K. 2009. Solutions to locoweed poisoning in New Mexico and the Western United States. Rangelands. 31(6):3-8.