Location: Poisonous Plant Research2012 Annual Report
1a. Objectives (from AD-416):
Objective I: Reduce risk of grazing cattle on larkspur-infested rangelands, and increase our understanding of aspects of cattle poisoning by various larkspur species. 1.1 Determine the interaction between ingestion of toxic alkaloids from larkspur and bloat in cattle. 1.2 Determine genetic differences to larkspur toxicity using a small animal model and genetically divergent cattle populations. 1.3 Determine clearance times and toxicokinetics of different toxic and less toxic alkaloid mixtures in small animal models and cattle. 1.4 Determine plant genotype and environmental influences on larkspur alkaloids and evaluate chemotaxonomy,chemical phenology, control strategies, and population dynamics of larkspurs. 1.5 Continue development of management strategies for cattle to safely graze on larkspur-infested ranagelands.
1b. Approach (from AD-416):
1.1 In the first phase, cattle will initially be screened for bloat susceptibility and for susceptibility to larkspur alkaloids. In the second phase, resistant and susceptible cattle will be tested for susceptibility to larkspur-associated bloat. In the third phase, mixtures of MSAL-type alkaloids and consecutive doses of larkspur will be administered at levels seen in field intoxication. 1.2 Strains of mice will be chosen to provide a diverse representation of minor haplotypes across the mouse genome, and lethality of MLA will be determined in each. The second series of experiments will examine the toxicokinetics of MLA in mice. Further work will characterize differences in gene expression between the selected mice strains (i.e., resistant and susceptible) after treatment with MLA. The differences in gene expression between strains will provide candidate genes to determine if susceptibility is heritable, and to identify genetic markers associated with MLA toxicity. 1.3 Initial work will examine the effect of deltaline on the toxicity of MLA by comparing the toxicokinetics and LD50 of alkaloids administered individually to mice vs. the co-administration of alkaloids at various ratios. Toxicokinetic studies will then be conducted to determine the kinetics of MLA, deltaline, or a combination of MLA + deltaline. Various body tissues will be collected and analyzed for alkaloid concentrations. After work on mice is completed, similar studies will be conducted using cattle. 1.4 Larkspur flowering stalks representing D. occidentale and D. barbeyi will be collected throughout their geographical distribution. A chemical fingerprint of alkaloids will be generated from each sample, and samples will be scored for the presence or absence of the MSAL-type alkaloids. Studies will elucidate the biological mechanism(s) responsible for the observed chemical fingerprints. Reciprocal gardens of D. occidentale plants representing both chemical fingerprints (putative hybrids and non-hybrids) will be established. Phylogenetic analyses using individuals representing D. occidentale and D. barbeyi plants containing little or no MSAL type alkaloids (i.e. putative hybrids) will be performed using AFLPs (Amplified Fragment Length Polymorphisms) to determine if tall larkspur plants that do not contain MSAL-type alkaloids are derived hybrids. 1.5 Studies will focus on one particular low larkspur, Delphinium andersonii. Grazing studies of cattle consumption will be conducted at two locations (Idaho, Nevada) for 2 years each from the vegetative to pod stages of growth. Study pastures will be delineated based on low larkspur density. The dependent variables will be daily bite counts of larkspur and other forage components. Bite counts will be taken during all active grazing periods. Larkspur density, biomass, alkaloid concentrations, and nutritional quality (i.e., NDF, IVOMD, CP) will be determined in relation to other forage components.
3. Progress Report:
Larkspur (Delphinium spp.) poisoning causes serious economic loss to livestock producers grazing cattle on foothill and mountain rangelands in western North America. Cattle death losses to larkspur are estimated to be 5 to 15% annually in areas where larkspurs are abundant and the clinical signs associated with larkspur intoxication in cattle are enigmatic. Quantitative measures of larkspur intoxication in cattle have been developed to assess the degree of intoxication and are currently being used to assess the susceptibility or resistance of different breeds of cattle to larkspur intoxication. Toxicokinetic and phenotypic screening of breeds has continued with the aim of increasing the numbers of evaluation breeds for genetic testing (Angus, Line 1 Hereford, Holstein, Jersey, and Brahman cattle). Preliminary results suggest that dairy breeds are resistant to larkspur intoxication. Additional toxicokinetic studies of various species of larkspur have been performed.
1. Early season risks for cattle grazing toxic larkspur species (Delphinium glaucescens). Previous analysis of a specific larkspur species (Delphinium glaucescens) indicated that it was highly toxic, but there was no information available describing the grazing preferences of cattle in pastures containing the toxic plant. A grazing study was conducted by ARS researchers in Logan, UT on pastures in the Salmon River Range Mountains near Challis, Idaho containing D. glaucescens. Cattle consumed toxic larkspur when the plant was vegetative and in the bud stages of growth. Consumption of only a few of the small plants was sufficient to intoxicate cattle. Unlike other tall larkspur species which grow in the presence of other herbaceous forages, D. glaucescens grows in drier sagebrush communities. The risk of cattle death losses in spring is high because of the very high toxic alkaloid concentrations in this larkspur species and its moderate consumption by cattle. This knowledge will help livestock producers limit cattle losses in larkspur-infested rangelands.
2. Fluctuations of toxic Larkspur species (D. andersonii) across the western U.S. Populations of D. andersonii, a toxic low-growing larkspur common to arid and semi-arid plant communities across the western U.S., fluctuate dramatically from year to year. However, there is little information available on the life history of Delphinium andersonii. Studies were conducted by ARS researchers in Logan, UT to determine the number of plants emerging from dormancy, plant height, the number of flowers (as measures of plant fitness) and alkaloid content. Plant fitness and other factors vary from year to year depending on precipitation. This information is important to understand major changes in D. andersonii populations over time, and to make recommendations to the livestock industry.
3. Behavioral response to larkspur-intoxication. The behavioral effects of two larkspur alkaloids (MSAL and MDL-type) were determined in mice in order to more clearly define the mechanisms of action in a whole animal model. Mice were dosed with purified alkaloids and were evaluated for physiologic and behavioral responses. The alkaloids had different behavioral effects, based on their differing sites of action and specific cellular receptors involved in toxicity. This research provides insight into specific brain pathways affected in mice dosed with larkspur toxins. This information is the first step in understanding why cattle graze larkspur and eventually find a means help livestock producers make more informed management decisions to limit losses to larkspur poisoning.
4. Toxicokinetic analysis of two low larkspur species. Delphinium andersonii (Anderson's larkspur) and D. nuttallianum (Nuttall's larkspur) are important toxic plants in Idaho and Utah respectively. ARS researchers at Logan, UT determined the clearance times of toxic alkaloids from both larkspurs so that an accurate assessment for each plant species can be made. This study documented differences in toxicokinetics of the larkspur and compared them to other previously examined larkspur. These results support the recommendation that approximately seven days are required to clear 99% of the toxic alkaloids from the serum of animals administered either species of larkspur.
5. Molecular mechanisms of larkspur toxin action. Larkspur toxins have been classified as blockers of a specific receptor in the brain. ARS researchers in Logan, UT, used genetically engineered mice lacking that specific brain receptor and evaluated three genetically distinct groups of mice for toxicity to larkspur. Results indicated that the specific brain receptor does not play a critical role in the lethal effects of the toxins. These results, in conjunction with other research performed in cattle by ARS researchers in Logan, UT, suggest that the mechanism of action of the toxic alkaloids in larkspur is via inhibition of receptors outside of the brain, i.e. neuromuscular receptors. This research will allow for the development of targeted responses to larkspur poisoning and better management of larkspur poisoning in livestock.
Frost, R., Walker, J., Madsen, C., Holes, R., Lehfeldt, J., Cunningham, J., Voth, K., Welling, B., Davis, T.Z., Bradford, D., Malot, J., Sullivan, J. 2012. Targeted grazing: Applying the research to the land. Rangelands. 34(1): 2-10.