Using plant species to combat wormer resistance
Internal parasites are a major challenge for听livestock producers. In sheep production systems听they听can reduce growth rates听and cause economic losses. Traditionally, anthelmintic drenches听have听been used to treat and control internal parasites, however the widespread development of anthelmintic resistance (AR) has increased the need for more sustainable parasite management strategies 鈥� such as the integration of bioactive forages into grazing swards.听
What is a听bioactive听forage?听
Bioactive forages are plants which听contain听natural compounds which can improve animal health as well as providing nutritional听value.听Bioactive forages are often included in swards referred to as herbal leys or multi species swards.听Some examples of bioactive forages include the legumes听sainfoin听(onobrychis听viciifolia) and听birdsfoot听trefoil (lotus听corniculatus), and the non-legume听chicory (chicorium听intybus)听which have all been found to reduce the negative effects of parasitism in sheep.听听
The bioactivity of plants is attributed to organic compounds which do not directly have a function in the primary metabolism of plants; i.e. affecting growth,听reproduction听or development. The compounds are instead known as plant secondary metabolites听(PSM),听such as condensed tannins (CTs),听which have both direct and indirect anthelmintic effects.听
Direct effects of CTs听include damage to听gastrointestinal听worms. The compound binds to proteins on the听worm听which damages their structure and therefore interferes with their metabolic function- reducing the viability of the听worm. The PSM can also prevent eggs from hatching or developing into larvae which reduces contamination of pastures. Studies have also concluded that by feeding bioactive forages the faecal-egg count听(FEC)听of a flock is significantly reduced.听
CTs can also indirectly increase protein absorption within the digestive system of a ruminant due to the CTs reducing the microbial breakdown of protein in the rumen.听This increases the proportion听of听bypass听protein that passes to the abomasum, where it is digested and听subsequently听absorbed by the host animal.
In addition to their antiparasitic properties, bioactive forages can also improve the energy and protein supply available to sheep. Chicory, for example, is drought tolerant and can provide valuable nutrition later in the grazing season when听pasture worm burdens are often at their highest. Although chicory has a low dry matter content, it is commonly grown alongside grass, clover, or plantain. This combination of improved nutrition and reduced parasite challenge shows strong potential within sheep production systems.听
Bioactive forages are not a complete replacement for wormers, but they could be integrated into a sustainable parasite management strategy. When used alongside good grazing management and targeted selective treatment, they could help reduce reliance on anthelmintic drenches whilst also supporting animal performance.听听
Katrina Coutts, Consultant,听Katrina.coutts@sac.co.uk
Posted by SAC Consulting on 16/06/2026
