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.
- Can sheep be conditioned to avoid feeding on koa foliage in a controlled setting?
- If the aversion is successful in confinement, will it persist in the field?
- How long will the conditioned aversion last?
- 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.
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.
We began the project with 25 sheep, 15 that would be averted with lithium chloride, and 10 that would be treated with water. Initially, we put al 25 sheep, along with a few goats who had previous exposure to koa (which prompted the other animals to overcome their resistance to the feed because of its novelty) in a holding pen with a central feeding bunk that we filled with koa foliage that we had gotten from the field. We weighed all sheep and fit the ones to be treated with collars that had an ID number. Whenever an experimental animal fed on a substantial amount of koa (more than 3-5 bites), we would retrieve the animal, treat it with water or lithium chloride, and then put into a side holding pen that was devoid of forage for two hours (this was to make sure no other forage was associated with the nausea caused by lithium chloride). On the next day, we tested the aversion by again offering all animals koa foliage.
Initially, we were planning to test the aversion on sheep in individual pens with a weighed amount of koa in a feed tub, then weigh the tub again at the end of a feeding period to see how much koa foliage either treated or untreated animals ate.
There were two problems with this: first, the koa foliage was freshly cut from the field and it was a hot, sunny day, and the pens were uncovered. This resulted in moisture loss from the weighed out koa tubs that influenced the weight of the koa, regardless of whether or not an animal had fed on it.
Second, these sheep were fresh in from remote rangeland, and their herd mentality was strong, which resulted in restlessness when confined to an individual pen and left to eat. This uneasiness severely affected feeding behavior, and most animals, even control animals, ate almost no koa from the offered tubs.
We overcame this challenge by releasing all animals (control and treatment) into a larger pen with a large amount of koa foliage in a central feeding bunk. Since the treated animals were collared and ID’d, and since the total number of animals was relatively small, we could easily observe if and when a treated animal fed on koa.
We took the treated animals to the field the next week, although we experienced one mortality (from preexisting condition of acute parasitism), and three other animals were able to remove their collars with ID numbers, making them indistinguishable from the rest of the sheep herd or control animals. So we ended up with 11 treated sheep for the field portion.
There were three replications of treatments (grazed, mowed, and control), and each grazed plot was grazed for 24 hours with the available animals. The plot size was set to have medium grazing pressure from the available number of animals. Mowed plots received treatment applications at the same time as the grazed treatments were being grazed. Pre and post measurements were taken on herbage mass, botanical composition, and sward height. Koa height and diameter at basal height were recorded prior to treatment application in all plots, and soil was taken from all plots for subsequent analysis.
On the first day after treatment, 10 of the 10 control sheep fed profusely on the offered koa foliage, while only 3 of the 15 treated animals fed reservedly. As soon as we observed a treated sheep feed substantially on koa (3-5 bites or more), we would readminister the same dose of lithium chloride.
We did this test again the next day, and this second time 10 of the 10 control animals again ate profusely, while 0 of the 15 treated animals fed on the offered koa whatsoever. Animals were also fasted overnight in each case.
For the field portion of the study which occurred about one week after initial treatment of animals, of the 11 remaining animals, 9 exhibited no feeding behavior on koa foliage. One sheep in particular ate a great deal, at first only after available forage became low, and then after that whenever the foliage was available. This lead us to believe that having adequate available forage is almost necessary for the aversion to persist. One other animal did some minor barking on trees in the plots.
These animals were identified on day 2 and were removed before grazing the third plot on day 3. Branches from koa trees in all grazed plots had been marked and leaves counted, and heavy leaf removal occurred in the first two replications, and zero in the third.
This result is not uncommon in previous studies, because feed aversions are rarely 100% effective on the population it is being applied to, because of the series of biological processes that make up the aversion, and the subjectivity of each individual animal. It is possible that the animal that was not averted did not associate the previous nausea with koa foliage, and it is also possible that the difference between bunk offered foliage/foliage on the tree rendered the aversion line fuzzy. It was, however, necessary to remove the animals that fed on koa from the group before other animals learned that they could feed on koa without deleterious results.
We have only completed the initial confined aversion and one grazing event. We have multiple more grazing events to conduct over the next few months where we will glean a better idea of aversion persistence and the effect of grazing on koa, understory, and soil characteristics relative to mowing or doing nothing.
Educational & Outreach Activities
No outreach activities have yet taken place because we are not finished with the field component of the study and do not yet have full results to share with the community.