Parasitic nematodes are a major problem for the sheep industry. Worms are estimated to cost the European dairy sheep industry EUR 151 million annually, and EUR 206 million to its meat sheep industry. Moreover, the nematodes are increasingly resistant to the antiparasitic drugs, or anthelmintics, used to keep them in check.
Alternative solutions are a high priority, recounts parasitologist Spiridoula Athanasiadou, Professor of Animal and Veterinary Science at the Food Security Challenge Centre of Scotland’s Rural College. “The way I’m looking at it is, we are developing a new tool. It’s good to have anthelmintics, and we will not be able to control worms without anthelmintics…but if we are able to have something else that we can use to reduce the use of anthelmintics and as a consequence, prolong their active use, that would be a very good outcome. And nutritional alternatives, such as the use of plant extracts, have, in my opinion, a very important role to play in exactly that,” she says.
Bark extracts
There is already some awareness that certain plant-derived active compounds, such as condensed tannins, can be useful in combatting parasites. However, using a purified plant metabolite is expensive. A more cost-effective and sustainable alternative would be deriving crude extracts from bark, a by-product of the forestry industry which is generally diverted to low-value applications such as being burned to produce energy. Better understanding of the chemical makeup, and thus the potential of these bark extracts to combat costly sheep parasites, is the goal of Dr. Athanasiadou’s research.
“Developing forestry by-products as a novel therapeutic for parasite control in ruminants”, the BBSRC* funded project that Dr. Athanasiadou is leading, has as its objective to identify as many antiparasitic compounds as possible, and to create an index. “[Once] we have a number of compounds that we know have antiparasitic properties, then based on these compounds [we’ll be] able to characterise a bark extract on its potential to be used as an anthelmintic supplement in animal feed, or not. So if we have, for example, an index of 10 compounds that are active against parasites, then at some point I’m hoping we will be able to say ‘bark that contains that much of A, that much of B, that much of C, and that much of D compounds is likely having good anthelmintic activity and we can use it for parasite control’,” she explains.
In the process, the team will be collecting bark samples from different places in the UK, and testing some basic extracts against the parasites in question. Those extracts showing antiparasitic activity would be further fractionated, with the aim to try and identify the extracts or fractions that are responsible for the bulk of the antiparasitic activity. However, she notes, they are not looking to reduce down to simple, highly-purified compounds, which would be quite expensive and thus more difficult to deploy at scale. “That’s why the extracts we’re going to be looking to characterise are going to be complex extracts. This project is not about looking at purifying extracts, or purifying single compounds with the aim, [for example], to have a new anthelmintic. The aim of this project is to characterise extracts in a satisfactory way to potentially be used as a feed supplement for nematode control.”
One of the major goals is helping to chart a way forward amid the variability in the chemical makeup of bark extracts, variability that comes not only from the diversity of tree species and location of growth, but also potentially from the season in which the bark was harvested, among other variables. “We will be collecting bark at different times of the year, to try and capture as much variation as possible,” she notes. “Variation in that case is not a problem, on the contrary. We just need to characterise the variation.”
Participants in the project include Saint Andrews University, University of Edinburgh and Biomathematics and Statistics Scotland, as well as actors from the forestry sector who are interested in seeing the development of higher-value applications for bark, and livestock industry representatives interested in alternative solutions to preserve anthelmintic effectiveness. It builds on preliminary work which Dr. Athanasiadou carried out alongside colleagues from Norway, which itself has a sizeable forestry industry funded by the Research Council of Norway and the BIONÆR programme (BarkCure project; Grant number 268264).
Future perspectives
The current research project is set to run for three years. But Dr. Athanasidou believes there is scope for much more research, particularly regarding the applications of these extracts.
For example, she says, it would be particularly interesting to complement the lab work which is the focus of this project with some in vivo trials, “just to see how it’s going to [work] in real life.” Past work using a plant-derived ingredient rich in condensed tannins has taught her that these products can have negative effects at high concentrations, so working out an appropriate dosage can be something of a balancing act “to try to gain from the antiparasitic effects of the bark extracts, but then not penalise animal performance.”
Moreover, beyond the current project’s specific focus on sheep nematodes such as Teladorsagia circumcincta, one could imagine this approach might potentially be extended to other parasites which the animal production industry struggles with, for example fluke in ruminants or coccidia in poultry.
Finally, she adds, while it might make sense for places like the UK or Norway to obtain such extracts from bark, the presence of the active compounds in other plants might make it possible for researchers to identify alternative paths to the same goal of an antiparasitic feed additive. “Other countries that might not have such a significant forestry industry may have other plants that can be used for similar purposes,” she concludes.
* Biotechnology and Biological Sciences Research Council, part of UK Research and Innovation
