This project was designed to quantify the plant secondary compounds in common forage and weed species found in range and pasture lands in Hawaii. The project developed a plant secondary compound database containing information on 40 species of plants. Specimens of these plants were collected, pressed, mounted and added to three herbariums housed in Kauai, Maui and Hawaii County Extension Offices. A field manual is being compiled, utilizing the information gathered in this project.
Weed and brush encroachment into Hawaii’s range and pasture lands remains a significant problem affecting the sustainability of ranchers in the state. Herbicides and mechanical control measures, the common techniques for weed and brush control, are no longer economically viable options at the landscape scale. Many ranches are looking for alternatives to costly herbicides and mechanical control measures. Multi-species grazing has proven effective for some ranches. The introduction of sheep and/or goats into the grazing operation in most cases has produced dramatic results in the control of weeds and brush for these operations. Moreover, it has increased the diversity of product the ranch markets, improving the economics of their operations. Other producers are interested in the possibility of using their cattle as a means to graze range and pasture plants previously underutilized or avoided.
Recent work by Dr. Fred Provenza and the BEHAVE group at Utah State University and others suggest that cattle and other animals can be trained and used to graze a greater diversity of plants in the pasture than previously thought. One critical issue to pursuing such a course is having an adequate understanding of the various plants available in the pasture system and the type and quantity of secondary compounds they contain, since it is these compounds that usually contribute to their low palatability and/or potential toxicity. Secondary compounds commonly found in range and pasture vegetation include alkaloids, tannins, phenols, terpenes and cyanide. Each of these compounds affects animals differently and is dependent on the relative concentration in the plant and the amount of plant ingested. Most of our understanding comes from, and is limited to, those plants known to contain toxic levels of these compounds. Yet at moderate levels, research has shown that these compounds may have benefits for grazing animals and, in some cases, may be complementary in the grazing diet. For example, tannins and alkaloids are found in several plants commonly grazed by livestock. Tannin may bind certain alkaloids in the rumen of the animal, reducing its toxicity.
Currently, however, very little is known about how widespread these compounds are in the vegetation common to range and pasture lands. Thus, the purpose of this project was to compile and disseminate information on the type and quantity of secondary compounds found in the diversity of vegetation common to range and pasture lands in Hawaii. This information is important in helping Hawaii ranchers formulate more efficient grazing programs that will utilize a larger diversity of plants. Targeted grazing of many plant species previously underutilized or avoided because of the presence of these secondary compounds will provide for improved grazing utilization of pastures and greatly reduce the need of costly herbicides and mechanical control measures used otherwise. Better grazing utilization of pastures results in better control of weed and brush encroachment into pastures, increased livestock productivity, improved pasture condition and helps maintain the ecologic and economic stability of the ranching operation.
The specific objectives for this project were:
1) Develop an online database, accessible to the public, listing common range and pasture plants, their nutritional value, secondary compounds and recommended grazing practices for utilization.
2) Establish a plant collection of the species in the database for identification and educational purposes that will be held in the Range and Pasture Plant herbariums, located at the county extension offices in Hawaii.
3) Produce a field manual for producers and land managers providing information on the plants in the database that will be useful for field identification of the plants and will also provide a summary of secondary compounds, forage value, recommend targeted grazing practices and cautions for utilization of the plant.
4) Develop targeted, behavior-based grazing practices for the plants in the database that will be presented in a series of fact sheets and extension service workshops.
At the beginning of the project, the Principle Investigator (PI), producers, Research Assistant (RA) and other project personnel met to compile a list of range and pasture plants to be included in an online database. The list was expanded from the planned 30 to 40 common forage and weed species in Hawaii range and pasture lands. Once the list was compiled, the PI and RA began developing a database referencing information from the literature on each plant. The database contains information on secondary compounds and other pertinent data. The database was also used to reveal gaps in the current knowledge about these plants and help focus our efforts to identify and quantify the secondary compounds they contain. Project personal collected samples of plants identified for the database over the first year of the project. These plant samples were pressed, dried and mounted for inclusion in herbariums located in three of the county extension offices in the state. Additional plant samples were collected to be analyzed for secondary compounds (approximately 20 plants) where the database indicated a gap in information. These samples were dried and ground, or frozen, depending on the type of secondary compound being tested for. The intent was to send the samples to an appropriate laboratory for testing for particular secondary compounds. However, this proved to be too costly and the samples were never tested. We began drafting a field manual containing all data collected in compiling the database and field collections of plant samples near the end of the second year. The field manual is not yet complete. Fact sheets providing techniques for establishing targeted, behavior-based grazing management programs are planned but not completed.
The project has resulted in over 40 plants specimens contained in three herbariums housed in the Kauai, Maui and Hawaii County Extension Offices. These herbariums are open to the public and are particularly targeted toward farmers, ranchers and other land management personal who wish to identify specific plants. The Plant Secondary Compound database is included on the Hawaii Rangelands website (http://globalrangelands.org/hawaii). While we had planned to have at least 20 plants analyzed for various secondary compounds, this task proved to be too complicated and costly as laboratories interviewed typically would not analyze the whole suite of compounds we were interested in or would not because of the limited number of samples we wanted analyzed. In the latter case, it was too costly for the laboratory to ramp up for an analysis of a compound for one or two samples. Consequently, none of the plant samples collected were analyzed, though we have retained the samples. Instead we relied on what we could find in the literature regarding various plant secondary compounds. Gaps still remain, but to close those gaps would require much more funding than previously anticipated. A field manual is in progress that will contain information gained over the course of this project on the secondary compounds of several of the more important weeds found in Hawaii. Completion of the manual is anticipated within the next six months and will be made available through open access on the Hawaii Rangelands website. Information on plant secondary compounds has been incorporated into the Hawaii Grazing and Livestock Management Academy program. This program is provided once per year to Hawaii livestock producers. The information and knowledge gained from this project will assist livestock producers in the identification of common plants found in most pasture systems in Hawaii that contain certain secondary compounds and provide recommendations for the utilization of those plants using targeted, behavior-based grazing management practices. The utilization of the knowledge and information from this project will help livestock producers make informed decisions about the sustainable management of their range and pasture systems.
Educational & Outreach Activities
Thorne, M.S., M. Abran, M. Stephenson, Secondary Compounds of Common Pasture Weeds of Hawaii. In progress.
1) Forty species Plant Secondary Compound database accessible at http://globalrangelands.org/hawaii)
2) Forty mounted plant specimens added to three herbariums located in Kauai, Maui and Hawaii County Extension Offices.
3) Field manual of plant secondary compounds of selected pasture weeds found in Hawaii currently being compiled.
4) Information compiled and incorporated into Hawaii Grazing and Livestock Management Academy.
Additional areas of study include utilizing targeted, multi-species grazing programs to manage pasturelands and how secondary compounds contained by the array of forages available across the range or pasture landscape interact to influence grazing behavior, distribution and intensity of the different livestock species.