Training Livestock to Eat Weeds in the Tropical Pacific and Evaluating the Effects on Meat Quality for Stronger Ranch Profits

Project Overview

Project Type: Professional + Producer
Funds awarded in 2011: $49,610.00
Projected End Date: 12/31/2014
Region: Western
State: Hawaii
Principal Investigator:
Matthew Stevenson
University of Hawaii

Annual Reports


  • Animals: bovine, goats, sheep


  • Animal Production: feed/forage, feed additives, grazing management, grazing - multispecies
  • Crop Production: food product quality/safety
  • Education and Training: demonstration, extension, on-farm/ranch research, participatory research
  • Pest Management: biological control, weed ecology

    Proposal abstract:


    We aim to redefine certain pasture plants in the tropics and sub-tropics not as weeds but as regular parts of livestock diets. If we are successful to this end, ranchers may reduce or eliminate herbicide use and thus lower production costs, maintain herbicide efficacy and greater safeguard human health. Ranchers and researchers have trained livestock in temperate regions to eat weeds that have high levels of secondary chemicals. Beef cattle production is the largest livestock industry in Hawaii, and effects of cattle eating weeds with high secondary compounds on beef quality have not been widely described. As flavor is among the chief factors influencing consumer acceptance of a meat product, we seek to evaluate any effects of these plant chemicals on beef flavor and quality. Furthermore, these training methods have not been systematically tested or demonstrated in tropical grazing environments. We proposed to evaluate and demonstrate the efficacy or limitations of this multi-species livestock training program by assessing short- and medium-term impacts on target plants, beef flavor and quality, effects on animal health and potential for rancher adoption in Hawaii.

    Problem and Need

    Attendees of the 2007 Western SARE sub-regional conference in Hawaii identified reduction of imported farm inputs as the leading type of research and education necessary to help economically sustain farming and the environment over the next 10 years. Costs of farm inputs such as herbicides in Hawaii and the Pacific Basin are high owing to great transportation distances. Incorporating different types of livestock in a grazing system to exploit inherent differences in their foraging behavior has had dramatic success in replacing herbicides for managing certain weeds. Despite these successes, some plants containing high secondary compounds remain problematic as livestock avoid them altogether or do not eat enough of them to check their increase in the pasture. The next step in grazing management for weed control in the tropics is to realize the idea that grazing animals can consume certain weeds if they learn how and get the right tools to cope with plant chemistry.


    Based on over thirty years of research by Dr. Fred Provenza and his colleagues, the BEHAVE Network has developed promising methods of training livestock to eat weeds of temperate regions using diet supplements and a systematic approach to introducing new foods into livestock diets. This approach dovetails particularly well with multi-species grazing strategies several livestock producers are adopting for weed management. These methods, still under development, have not been systematically tested and demonstrated across pasture types in tropical Pacific islands. Rigorous studies by members of the BEHAVE Network demonstrated that animals can and will eat substantially more of plants high in secondary compounds, which can be toxic at too high dosages, than researchers, ranchers and professionals have believed. Livestock showed no ill effects from eating diets high in secondary compounds when they had access to alternative forages and adequate supplementation to increase the rate of detoxification. There is ample evidence that ingesting a diverse array of plant chemicals is critical in the nutrition and health of livestock and humans, and that these compounds in the diets of livestock can improve the flavor and quality of their meat for human consumption.


    By experience and in consultation with other ranchers, we have identified the following species as weeds to target for control with livestock grazing: Ageratum conyzoides, Asclepias physocarpa, Cymbopogon refractus, Psidium cattleianum, Schizachyrium condensatum, Senecio madagascariensis and Sphagneticola trilobata. Our hypothesis is that by offering animals appropriate training and positive experiences eating weeds, they will subsequently include these weeds in their diets while grazing. We will send samples of these plants for nutritional and toxicological analysis so as to prepare the best supplementation program, if necessary, to help them eat these plants. Using 8-10 head of breeding heifers and 8-10 head of market cattle, sheep or goats at each ranch, we will set up temporary pens to feed and observe animals during a five-day training period designed to increase livestock acceptance of the weeds. At the time of training, we will establish baseline levels of utilization, cover and density of target weeds on the study pastures and monitor these features on a quarterly basis for the duration of the three-year project period. We will monitor animal health by rancher observation and blood sample analysis. A taste panel will compare flavor of beef samples from trained livestock with samples from untrained livestock foraging on pastures of similar plant communities. Chemical analysis of compounds known to influence beef flavor will provide quantitative data to pair with the flavor assessment.


    The intended net effect and goal of this training program are to reduce production costs, thereby increasing ranch profitability, increase pasture use efficiency and provide a high-quality product for human consumption. We will further understanding and development of these methods, and if successful, ranchers will have another option to further reduce herbicide use for weed management.

    Project objectives from proposal:

    1) Trained cattle, sheep and goats will consume unfamiliar foods.


    - Collect blood samples before training period, at end of training period and three months following initial training to monitor animal health.
    - Feed a high quality food already known to the animals in the morning. In the afternoon add an unknown feed of high quality to the known feed.
    - Repeat over five days, introduce the target weed species on the last two days.
    - Observe animals’ consumption of weeds under field conditions for two days following training period and for two days during quarterly follow-up visits over the course of the three-year project.

    2) Livestock offered a free-choice diet supplement of tannins, terpenes, protein and energy will be able to consume weeds with high levels of secondary compounds.


    - Provide up to 1% of daily diet on a dry-weight basis per animal of above supplements during training period.
    - Monitor supplement consumption by weed fed.

    3) Targeted weed populations will decrease with increasing grazing pressure from trained livestock.


    - Using eighteen 100 meter transects per ranch, monitor cover, density, aboveground production and utilization of target weed species found within and outside training pasture on a quarterly basis over the three-year project.

    4) Effects of consuming weeds on meat quality will be detectable.


    - Tenderness will be assessed with shear force analysis using a Warner-Bratzler blade.
    - Flavor will be assessed by blind taste tests using a taste panel.
    - Fatty acid profiles will be compared among longissimus dorsi samples from trained and untrained livestock.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.