Initial results from a study at the Agri-Food and Biosciences Institute (AFBI) show potential for the practice of targeted selective treatments for parasites.

AFBI report that the study, which is being carried out at its Loughgall premises, found that “when targeted selective treatment (TST) was used almost 75% of treated animals showed an improvement in daily liveweight gain”.

The study is part of a wider Co-Adapt project led by Queen’s University Belfast which aims to give farmers greater confidence in managing parasites sustainably. It aims to use relevant information to support animal performance and long-term wormer efficacy.

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While the full analysis is still underway, AFBI says the emerging patterns offer useful insights for sheep farmers looking to manage worm burdens more.

“Although more detailed findings will be released once the analysis is complete, AFBI researchers have said that TST appears to be both workable and effective in a grazing lamb system, provided farmers take a flexible approach and review decision points as the season progresses and conditions change”.

Study metrics

As part of the first year of the study 48 weaned lambs grazed a perennial ryegrass and clover sward in a rotational grazing system from July to September 2024.

Lambs were dosed when they met TST criteria based on growth rates, faecal egg counts or dag scores – measures which AFBI highlight are familiar and practical to most sheep producers.

It said: “Almost every lamb required at least one treatment during the season, and most needed two, but the biggest trigger by far was reduced liveweight gain.

“This performance-based cue proved to be the most reliable indicator that a lamb was struggling with parasite challenge”

Study results

AFBI went on to add researchers reported that around 74% of lambs that received a dose subsequently increased their daily liveweight gain, highlighting the potential of TST to direct treatments precisely where they are most effective.

This early trend suggests that carefully targeted dosing can support lamb performance while avoiding unnecessary treatments — a key tool in the battle against anthelmintic resistance”.

Dr Aurélie Aubry, head of sheep research at AFBI, was one of the leading researchers on the project. She said sheep farmers are facing significant challenges around managing parasites.

This study forms an important contribution towards helping farmers face those challenges. With a targeted selective approach, a proportion of the flock is left untreated, which reduces drug use and costs and slows the emergence of resistance to worm treatments.”

The study is also examining how gastrointestinal nematodes and coccidia interact, and how these co infections influence lamb growth and pasture contamination.

This analysis is ongoing and will form important learnings for farmers with mixed parasite burdens common on sheep farms but their effect on treatment requirements and performance is not fully understood.

Handling facilities

The update shows that good handling and weighing facilities proved essential during the study.

“Regular monitoring was needed to make confident treatment decisions, and AFBI emphasised that any farm considering TST will need reliable systems for weighing and recording.

“Without these, it becomes much harder to identify which animals genuinely need attention.”