The first year of results from an AgriSearch-led project that seeks to assess the feasibility of implementing new approaches to the use of anthelmintics on cattle and sheep farms has highlighted some realities when converting theory into practice.

The aim of the project is ultimately to extend the life of wormers amid the growing threat of resistance to the various products available on the market.

To achieve that, it is important to have a reservoir of worms on farm not exposed to anthelmintic treatment, so that they can mix in and interbreed with resistant worms.

Outlining the issues at last Thursday’s sheep breeders round table conference, Professor Eric Morgan from project partner QUB said one option was to implement Targeted Selective Treatment (TST) of individual animals on the seven project farms.

It sounds very simple. Where it gets complicated is when you try to apply it on real farms

It relies on the fact the majority of animals have very low worm burdens that won’t be impacting on production. Instead, the parasites tend to be concentrated in a few hosts.

“If we can identify those individuals, we can treat just those, and maintain a reservoir of susceptible worms. It sounds very simple. Where it gets complicated is when you try to apply it on real farms,” acknowledged Morgan.

One way to do that could be to regularly weigh animals and only treat those with poor weight gains, but to achieve that in practice requires a sophisticated handling system.

Instead, the farmers in the project opted for targeted treatment of groups of livestock based on faecal egg counts, but rather than treat immediately, they waited until some level of egg shedding on pasture was evident, to ensure non-resistant worms are still available.

They have achieved great things

On the farms, the total number of anthelmintic treatments was reduced compared to previous years. The study is to run for a second year in 2022.

But while the farms did not opt to use TST, Morgan believes that it still has a role in the selection of breeding stock, pointing to work done in New Zealand where farmers have bred from animals that need the least intervention.

“They have achieved great things in South Island Romneys going from needing 6/7 treatments in lambs, to zero to one,” said Morgan.

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