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


    Given exceptionally high transportation costs, Hawaii ranchers and farmers have asked for more research and education on reducing or eliminating off-farm inputs. The cost of pasture weed control can greatly reduce ranch profitability, and inadequate weed control leads to unacceptable production losses. Multi-species stocking has greatly improved pasture use efficiency through differences in grazing behavior, though some plants remain problematic. A U.S. mainland developed method to condition grazing preferences shows good potential for expanding livestock diets but has been untested on tropical plants. The purpose of this project was to evaluate this training method for application on priority tropical weeds in a demonstration proof-of-concept approach. We attempted to train multiple classes of cattle, sheep, and goats to eat nine species of tropical plants previously avoided. These livestock successfully ate seven of the targeted species in test troughs and paddocks: Amaranthus spinosus (L.), Digitaria insularis (L.) Mez ex Ekman, Elephantopus mollis Kunth, Leonotis nepetifolia (L.) R. Br., Persea americana Mill., Schizachyrium condensatum (Kunth) Nees, and Sphagneticola trilobata (L.) Pruski. Senna occidentalis (L.) Link was rejected for testing owing to several reports in the literature of acute toxicity, and despite conditioned preference training, goats did not eat the base parts of Asclepias physocarpa (E. Mey.) Schltr., though sheep ate leaves in later training. Blood tests did not reveal any undue stress during the weeklong training period. Weed populations did not appear to change during the study period. One collaborating ranch was successful in adapting the initial training method as well as providing an energy supplement to increase cattle intake of a pasture weed. The U.S. mainland developed behavior modification method appears to increase cattle, sheep, and goat intake of various weeds of concern in Hawaii. Longer term impacts on established weed populations and long-term effects on livestock health should be priority areas of study to further refine this approach for application in practice. At least one collaborating ranch has adopted this training method for their operations and post-workshop evaluations indicated other rancher interest in this method.


    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 on top of application costs. Incorporating different types of livestock in a grazing system to exploit inherent differences in foraging behavior has had dramatic success in replacing herbicides for managing certain weeds. Despite these successes, some plants 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 eat certain weeds if they learn how. The purpose of this university-ranch collaborative proof-of-concept demonstration project was to evaluate a North American developed approach to train livestock to eat pasture weeds in a tropical environment.

    Project objectives:

    We sought to achieve four objectives:

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

    Training cattle, sheep, and goats to eat a number of previously avoided pasture weeds, at least briefly in a test pen, has by and large been successful at four ranches. Detailed results for each site and species are reported below.

    2) Livestock offered a free choice diet supplement will be able to eat weeds with high levels of secondary compounds.

    This approach, offering a supplement such as a powder form of condensed tannins that may attenuate plant secondary compounds, was considered for increasing intake of Senna occidentalis at Kapapala Ranch. However, literature reviews revealed this Senna species to be highly toxic to cattle and goats. Given the success of goats controlling other target weeds, we decided to drop this plant from consideration. Energy supplements in the form of cracked corn and molasses were used at Haleakala Ranch for training cattle and sheep onto Digitaria insularis and Leonotis nepetifolia. Livestock readily ate both target species after overcoming neophobia via conditioned preference training.

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

    We monitored plots established at three ranches and set up short-term photo-monitoring sites at a fouth. Most data showed modest changes in weed and dominant species cover or density over the project period. Several paddocks have low stocking densities and weed populations are patchy. Under these conditions, it has been difficult to tell if the lack of weed patch expansion has been due to grazing pressure, competition with dominant pasture species, or an environmental response. Regardless, ranch managers were glad to see no noticeable increase in weeds of interest compared to previous years. Photo-monitoring of more intensely grazed sites showed noticeable impacts on target weeds, though long-term grazing management strategies for control and monitoring were outside the scope of this observation and proof-of-concept project.

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

    This objective became untenable for reasons described in the following sections.

    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.