Programme farmers from both phases of Dairylink Ireland discussed parasite control and wormer resistance during an online meeting last week.

Dr Dave Bartley from Moredun Research Institute in Scotland advised Dairylink farmers to find out if the wormers they use are actually working or not.

“Research is indicating that there are more and more issues with resistance to anthelmintic products,” he said.

Taking dung samples for a faecal egg count (FEC) before administering a wormer will let you know if a treatment is necessary.

Carrying out another FEC two weeks later and comparing the two sets of results will show how effective the treatment has been.

While FEC are more commonly used for diagnosing problems with gutworms, Bartley said the exercise has an important role in lungworm control in youngstock too.

Eggs counts are useful for lungworm control, especially in first-season grazers

A problem can be that during the early stages in its life cycle, lungworm eggs are not present in faeces, so a negative FEC result will not always mean that lungworm are not present. It can just mean that the lungworms have not started producing eggs yet.

“Eggs counts are useful for lungworm control, especially in first-season grazers. Once you get to adult cattle, they don’t work quite as well,” Bartley acknowledged.

Product type

Dairylink farmers were reminded that using a product that some worms have resistance to will mean only resistant worms are passed out on to the grass.

This is particularly worrying if cattle are moved to clean grazing, as only resistant worms will be on the pasture.

Repeated use of the same product will also lead to resistance issues

“If cattle have been dosed and moved straight to clean grazing, it is definitely worth knowing that the treatment has worked,” Bartley said.

Repeated use of the same product will also lead to resistance issues. When switching wormers, make sure that the new product has a different active ingredient, and is not just a different product name with the same chemical compound.

Bartley said some active ingredients are quite similar and so overuse of two or three different products can eventually cause resistant worms to build up.

“Mectins have very similar mechanisms for developing resistance. For example, if you have issues with resistance to ivermectin, then doromectin might work for a little while but you will start to see issues with it too,” he maintained.

Liver fluke

Bartley said that liver fluke is more difficult to detect through FEC as the parasite does not shed eggs on a consistent basis. However, blood tests and bulk tank milk sample tests are available for liver fluke detection.

It’s like footsteps in the snow because it tells you that the bugs were, or still are, there

Sarah Campbell from MSD Animal Health recommended the use of bulk tank tests at least once every three months. The test detects past exposure to a wide range of diseases as it finds the antibodies that were used by cows to fight specific infections.

“It’s like footsteps in the snow because it tells you that the bugs were, or still are, there. However, it doesn’t tell you exactly when the infection was there or who had it,” Campbell said.

“Bulk tank testing fits in well because it is easy to do and gives you a broad view of health issues within your herd,” she added.

Taking samples during the 2021 grazing season

Collecting dung samples to send for a FEC requires much less effort than many farmers initially think, Dr Dave Bartley told Dairylink participants last week.

He pointed out that dairy farmers will be out checking youngstock at grass anyway, so taking a few samples will not take up much more time.

The best time to collect a fresh sample is when an animal stands up and dungs after being disturbed from lying.

The equivalent of four heaped dessert spoonfuls should be taken from each animal.

It is the most cost-effective way and works well if done properly

Samples should be put in individual zipper storage bags and around 10 should be taken from each management group.

“Give the 10 samples to your vet in separate bags and they will be able to do a composite by mixing them up and doing a single egg count. It is the most cost-effective way and works well if done properly,” Bartley said.

The samples should arrive with the vet within two days and information about the animal type and previous treatments, plus details of any coughing, scouring or reduced performance should be stated.


Dairylink farmers were advised to wait between three to six weeks after turnout before carrying out the first FEC of the 2021 grazing season.

“Go at three weeks at the earliest, but six weeks is a sensible time frame, unless you have had problems early on in the past,” said Bartley.

Weekly round-up

  • Cows had to be rehoused on some Dairylink Ireland farms this week following cold and wet weather.
  • Grass growth rates have also levelled off, with the highest rate of 43kgDM/ha/day recorded in Co Down.
  • Programme farmers are planning to faecal egg count youngstock around six weeks after turnout.