Parasite project helps dairy farm to improve worm control

A Ceredigion dairy farm is revising worming protocols for its replacement heifers after a parasite control research project detected early stage resistance to clear wormers.  

The Jenkins family, who milk 400 New Zealand Friesians at Pentrefelin Farm, Talsarn, outwinter 210 R1 and R2 heifers on deferred grazing. This system increases vulnerability to roundworms because it limits opportunities for clean grazing in the spring.

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The research project will run for three years and involves two other dairy farms in the region.

About the project

At Pentrefelin, two wormers – benzimidazole oral, a white wormer, and ivermectin injectable, a clear wormer – were tested on 15 calves. Faecal egg counts (FECs) were recorded before and after treatment.

Resistance testing using full faecal egg count reduction tests was carried out by the farm’s vet practice, Steffan Vets, Lampeter, using Techion UK’s FecpakG2 system.

If a wormer is fully effective, egg counts should drop by a minimum of 95%, explains Eurion Thomas, of Techion UK, who is working with the farmers on the European Innovation Partnership project.


Although egg counts had reduced by 100% in calves treated with benzimidazole oral, they reduced by only 81% in the group given the ivermectin injectable.

White and yellow wormers were shown to be fully effective.

Mr Thomas says that at this stage the results point to a failure in treatment efficacy rather than true wormer resistance.

Irfon Jenkins, who farms with his brother, Eurig, and their parents, Aeron and Glenys, admits the findings were a surprise, not least because heifers were growing.

The worms present in the pretreatment samples were the two most common species, ostertagia and cooperia oncophora.

The species that survived was cooperia oncophora, which is less pathogenic and has less impact on performance.

This is likely to be why heifer growth rates were not affected too badly when the wormer didn’t fully work. Heifers at Pentrefelin achieve an average daily liveweight gain of 0.7kg from birth to calving at 24 months.

Next steps

The project will now examine if better control of worms can further improve this performance.

Mr Jenkins says he will now be far more selective in the use of the clear group of wormers and he may make some changes to heifer grazing policy, with clean grazing provided on reseeds in the spring.

He is also being more proactive with dung sampling. “We had been FEC testing before this project but not regularly enough,’’ he admits.

In future, heifers will not be dosed routinely, only when egg counts show treatment is needed, with the exception of a routine lungworm treatment in late summer or early autumn.

During the course of the project, disease modelling will be used to estimate relative pasture contamination levels at the end of the grazing season to inform grazing plans for the following year, such as which fields can be safely grazed and which should be cut for silage. 

Mr Jenkins says it is important that dairy farmers learn lessons from the sheep industry and the progress it is making on addressing anthelmintic resistance.