Abstract
Subclinical parasite infections in livestock production have huge economic impact on the farming industry, leading to decreased animal welfare and reduction in meat, milk and wool production. The global spread of anthelmintic resistance has exacerbated the threat of gastrointestinal nematode (GIN) infections to small ruminant health and production. Phytochemicals, such as condensed tannins (CT), have shown promising anthelmintic potential, and could complement other management practices to reduce anthelmintic use for parasite control. Conifer bark is a rich source of CT. Studies have shown that the content of CTs in Norway spruce and Scots pine varies, but on average they contain around 4% CTs. This study explored the anthelmintic activity of bark from Norwegian conifers over two seasons, extracted with three different solvents (water, acetone, methanol), against two sheep GIN, Teladorsagia circumcincta and Trichostrongylus colbriformis. Bark extracts were analysed to determine their total CT content and tested in vitro, with the aim to quantify their impact on egg hatching and L3 larval motility. Results show significant variation in efficacy of the extracts on egg hatching in a dose dependent manner. The CT content of the bark extracts were not always associated with LD50 values, indicating that other plant compounds may have additional anthelmintic effects. Preliminary results of the L3 larval motility test showed that incubation in the bark extracts had a smaller impact on this parasite stage at the concentrations tested. This research brings new insights into the potential anthelmintic activity of different phytochemicals and discusses the potential of bark extracts as a tool in the sustainable control of GIN in small ruminants.