Planning ahead is key to prevent wormer resistance in cattle

Cases of wormer resistance in cattle have increased over the past year, according to expert, Sally Harmer, who outlines steps that producers can take to minimise the risk to their herds.

The practice of faecal egg counting (FEC) to determine worm infestation levels in sheep is well established, but it is not commonly included in cattle management programmes, says Ms Harmer. However, the growing threat of wormer resistance within the national herd means that advisers are encouraging cattle producers to carry out FEC before putting a worming strategy in place for this autumn.

“Most producers will have given their cattle a long-acting anthelmintic at turn out,” said Ms Harmer, an animal health consultant. “Worm eggs will not develop into infective larvae in hot, dry weather. In situations where there is low rainfall in the run-up to housing, the risk will be relatively low, while a wet spell will increase the likelihood of a worm burden. Even a heavy dew will provide sufficient moisture to allow the cycle to begin.

Sally Harmer, animal health consultant

“Young cattle are the most vulnerable to worm infestation because their immunity levels are lower and they should be given priority for the cleanest pasture, which would include silage aftermath and reseeded grassland. Fields that have been grazed by sheep are also relatively low risk, as they will have consumed some of the worms while grazing and will leave it cleaner for the incoming cattle.

“Despite the advice to confine young cattle to low-infestation pasture, it is important that they have mild exposure to worms, as this will promote their natural immunity. Low-risk grazing will still contain some degree of worm infestation and this exposure will offer protection at turn out in the following year.”

Producers who intend to practise FEC will need to bear in mind that most worm species develop into adults on a 16 to 21-day cycle, she says. The weather will also have an influence on decision making.

Farmers are being urged to adopt strategic worming programmes

“FEC should therefore be carried out 16 to 21 days after a period of rain. Each sample should contain about one tablespoon of dung and placed in containers that will need to be kept in the refrigerator until they are examined on-farm, or sent away to the vet or laboratory for analysis. This will keep them fresh. Otherwise there is a chance that the eggs will hatch into larvae and the sample will be unusable. If they are to be posted, avoid sending them out on a Friday, or over the weekend.

“An anthelmintic should be considered if samples contain more than 250 eggs per gramme; certainly for the youngstock. Unless there are other health issues, adult cattle tend to have natural protection against worms and carrying out FEC may indicate that there is no need for treatment.”

The general pattern is to worm cattle at turnout and again during mid-summer, when the effect of the long-acting first treatment is waning, she stated. Producers who wish to reduce the potential for wormer resistance should test their herds in late season, with the aim of omitting the routine ‘third’ worming dose at housing for adult cattle.

Rotating the wormer type is another method of minimising the development of resistance, she adds, while dosing must be as accurate as possible.

“Care must be taken to make sure that the dosage rate matches the weight of the animal. The easy-to-use pour-on wormers carry a greatest risk of under-dosing and this in turn can lead to resistance. Poor application can result in as much as 30 per cent of the medication failing to act effectively in some cases.”

Liver fluke presents a serious threat to cattle health in the autumn, stressed Ms Harmer.

“I would strongly recommend that cattle, which are grazing in the wettest areas, which present the greatest risk of fluke, are tested for the parasite around housing time to ensure that products are not used unnecessarily,” she says.

“The presence of fluke can be established through a blood antibody test, or by testing dung for fluke eggs or antigens. The parasite has a ten to 12-week cycle, so the timing of testing is important in order to avoid a false positive or negative result.

“Some of the injectable and pour on wormers contain a flukicide while others do not, so it is worth checking which stages of fluke are covered before purchasing a product. In addition, among the range of flukicides there is only one that will control all stages of the worm. Therefore it is best to take advice from your animal health advisor before embarking on a fluke management programme.

“The cattle industry is encouraging producers to adopt strategic worming programmes to tackle the issue of wormer resistance and producers themselves have a responsibility to take an active role in the campaign. It is in everybody’s interest to ensure that we have continued access to effective wormer products,” says Ms Harmer.