2013 Annual Report
1a.Objectives (from AD-416):
The purpose of the studies proposed here are to investigate the impact of fireweed density on forage availability, consumption, and toxicity of fireweed in cattle, and to examine the possible role of CT in binding toxic plant compounds like pyrrolzidine alkaloids (PA). This project will address TSTAR goals 1, 2, 6, and 7. Specifically this project will investigate innovative and proactive management strategies for the control of an invasive weed, fireweed, in range and pasture lands of Hawaii (7). The information from this project will be used to develop decision-support materials for producers (6) that will provide environmentally sound management practices (2) that will enhance the overall productivity and sustainability of the livestock industry in the State. The specific objectives of this project are:
1) Determine the threshold density of fireweed within pastures and concomitant reductions in available forage that result in increased consumption by grazing cattle.
2) Determine the toxicity of fireweed to cattle; investigate the ability of CT to bind PAs in an in vitro system, and further determine the toxic effects of fireweed PAs in cattle with and without the potential ameliorating presence of CT.
3) Develop and disseminate a series of best-management practices for grazing cattle on fireweed infested range and pasture lands that will minimize PA poisoning and effectively control the spread of fireweed.
1b.Approach (from AD-416):
This research project will be carried out in cooperation with a producer on Maui utilizing small paddocks located in fireweed populations to investigate how plant density and available forage influence consumption rates in cattle. Blood serum levels of specific enzymes indicative of PA activity in the liver will be monitored and correlated to changes in plant density, forage availability, and animal performance to determine factors that affect the fate of PAs in the animal. Toxicology and grazing and in-vitro rumen digestion trials will be used to a) characterize the toxicological response of cattle to PAs in fireweed, and determine potential binding of CT and PAs in vitro; b) determine if the adverse effects of PAs are ameliorated by adding CT to animals’ diets; and c) through an additional grazing trial determine if cattle provided CT supplementation will willingly graze fireweed in a pasture environment. Again blood serum levels of indicator enzymes will be monitored to determine the relative toxicity level experienced by grazing animals. The information generated by these research trials will be compiled into a series of best-management practices and disseminated via presentations, and extension and journal publications to producers and the scientific community. All animal studies will be conducted under veterinary supervision, and protocols will be approved in advance by the IACUC at the University of Hawaii and Utah State University (for USDA-ARS, PPRL work).
Identification of toxic doses of fireweed in cattle. Senecio madagascariensis (fireweed) is an invasive toxic plant that contaminates much of the Hawaiian Islands rangelands. The plant contains a complex mix of toxic PAs. A study was conducted by ARS scientists in Logan, UT to determine the effect of chronic dosing of the PA mix on toxicity to cattle. Cattle that were dosed with medium to high doses of fireweed for 100 days developed liver damage that would affect production efficiencies. This research identified specific serum enzymes that are significantly elevated in fireweed poisoned animals. Pathological examination of liver tissues is ongoing, and preliminary results suggest a dose response from the combined alkaloid mixture in the plant. A study was conducted to determine the effect of feeding supplemental condensed tannin on toxicity of fireweed. Liver and serum samples from this study are currently being evaluated. The information can be used by livestock producers to identify chronically poisoned animals, as well as to make risk assessments of fireweed contaminated rangelands. Further, continued characterization of the individual pyrrolizidine alkaloids contained in fireweed is ongoing, as advances in chemistry allow for individual alkaloid identification.