Gastrointestinal nematode (GIN) parasitism is a highly prevalent endemic disease in grazing livestock that results in reduced growth and productivity, penalties in animal welfare and a predisposition to secondary bacterial infections contributing to antimicrobial resistance. These challenges are currently mitigated through chemoprophylaxis, however, resistance to anthelmintics is limiting the scope of its mitigation potential1. To tackle global challenges that hinder food production sustainability, including antimicrobial resistance, climate change and maintenance of biodiversity, it is critical that the rate of productivity and profitability can be maintained. This must be done without jeopardising livestock health and with minimum drug input, so that the lifespan of effective drugs is extended.
Plant secondary metabolites (PSM), such as condensed tannins (CT), are able to disrupt the nematode life-cycle at various stages (in the animal and in the environment) and consequently could contribute to parasite control. Many different PSM have been described2 and although they are present in all plants in small amounts, only a small proportion of plant species contain PSM in high concentration3. We and others have demonstrated PSM supplementation can reduce the level of internal parasitism and improve the resistance and tolerance of parasitised animals4-10. The bark of several coniferous species growing in the temperate climate zone is rich in PSM and a good source of CT. We recently showed that Norwegian pine bark extracts contain 3-8% CT whereas spruce bark extracts contained 1-7% CT11. The UK has a strong sawmill industry, where bark is a by-product. It is estimated that a total of 12.2 million green tonnes of roundwood was removed from UK woodlands in 2018 (Forestry Statistics 2019). Softwood accounted for most (93%) of the removals from UK woodland and totalled 11.4 million green tonnes in 2018. Forty percent of felled timber in the UK is processed in a sawmill to give co-products that include wood chips, sawdust and bark (https://secure.fera.defra.gov.uk/treechemicals/review/markets.cfm). This indicates that hundreds of thousands of tonnes of bark are available from forestry, most of which is currently burned or used in horticulture. Extraction of high value antiparasitic compounds that can enrich livestock diets, represents a significant potential for increased value creation from bark. As an example, and based on evidence generated from our previous work, extraction of 50 % of the CTs from 200 000 m3 of bark could yield 3.5 tonnes of CTs. If this was used as a dietary inclusion at 6 wt % per Kg of Dry Matter (DM) feed, a ratio that is active against parasites in sheep, it would provide enough CT to treat all UK sheep in late gestation and early lactation.
The exact PSM content, concentration and structure in a bark extract directly affects the extract’s biological activity and these factors depend on environmental conditions, including geographical location of the source wood and herbivory patterns11. To date, incorporation of PSM-rich extracts for parasite control has been hampered by this variation in PSM content, which results in variation in biological activity and thus inconsistency of effect. The delivery of a tool that can assess the anthelmintic potential of bark extracts will address this inconsistency. Once complete, this project will allow the creation of a realistic strategy for an integrated biorefinery based on the use of bark that can be applied on an industrial scale, to contribute to parasite control in livestock. This development will benefit two key UK industries, forestry and livestock production, addressing and solving significant challenges.
Contact details:
Dr Spiridoula Athanasiadou
SRUC