Conditioning Sheep to Avoid Koa Foilage: An opportunity for productive silvopasteres in Hawaii.

Project Overview

Project Type: Graduate Student
Funds awarded in 2018: $24,920.00
Projected End Date: 07/31/2019
Grant Recipient: University of Hawaii - Manoa
Region: Western
State: Hawaii
Graduate Student:
Principal Investigator:
Rebecca Ryals
University of Hawaii - Manoa


  • Agronomic: grass (misc. perennial)
  • Additional Plants: native plants, trees
  • Animals: sheep


  • Animal Production: grazing management, rangeland/pasture management
  • Crop Production: silvopasture
  • Production Systems: integrated crop and livestock systems

    Proposal abstract:

    Koa (Acacia koa), a native Hawaiian hardwood tree, has undergone vast reductions in population over the last 200 years from grazing and human activities. Replanting of koa has gained momentum over the last two decades for both conservation and production reasons, since koa provides ecosystem services and the timber is exceptionally expensive. In conservation or silvicultural settings, a major obstacle to koa establishment is competition of juvenile trees with weeds. The management options for this include mowing, herbicide application, or combinations of both, which are costly and hazardous to the environment. Another option that has received zero investigation is grazing the competitive understory with ruminants, after creating a conditioned feed aversion to the palatable, nutritious koa foliage. I will study the efficacy of conditioning sheep to avoid feeding on koa using Lithium Chloride (LiCl), a nausea-inducing chemical. The conditioning process requires a controlled setting, therefore after conditioning animals in pens I will evaluate if the aversion persists in a planted stand of koa. The length of time an aversion lasts has large variability, therefore I will quantify the persistence of conditioning.

    Research Questions:

    1. Can sheep be conditioned to avoid feeding on koa foliage in a controlled setting?
    2. If the aversion is successful in confinement, will it persist in the field?
    3. How long will the conditioned aversion last?
    4. What effects will grazing a koa silvopasture have on koa and nutrients?

    If aversions to koa foliage can be developed in sheep, producers can diversify and increase income while at the same time reducing negative environmental impacts. I will communicate the project results in printed protocol pamphlets handed out at demonstration field days held on Haleakala Ranch, publications in scientific journals, and presentations at national meetings.

    Project objectives from proposal:

    Our objective is to condition sheep to avoid feeding on koa foliage in a young koa stand with non-native grass understory. We hypothesize that grazed koa silvopastures will have enhanced koa growth due to suppression of competition from understory grasses and higher concentrations of plant available nutrients in soil.

    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.