Despite the prolonged periods of dry weather last summer, it does not mean that farmers can forget about the risk to cattle and sheep from fluke this autumn and winter. The risk might be greater than it first seems.

Last winter was generally mild and wet, the ideal conditions for overwinter survival of fluke stages on pasture and survival of the mud snail, the host for the life cycle of liver fluke.

In some parts of NI, heavy rain during August will have been ideal for larval development within the snail, while the dry weather in September will have meant that cattle and sheep may have grazed out parts of fields that would normally be too wet for grazing in the autumn (parts of fields that could carry heavy infestations of mud snails).

The advice from Dr Philip Skuce, a researcher from the Moredun Research Institute in Scotland, is to make use of all available information to form a strategy to control fluke this winter, in consultation with your local vet or suitably qualified animal health adviser.

The information to consider includes whether there is a history of fluke infection on the farm and recent abattoir returns showing damage to livers due to fluke. “It might also be good practice to take a few faecal samples along to your vet for analysis of the fluke burden – ideally, a representative sample from six to 10 animals, not just poor doers,” he maintains.

The cost of chronic fluke infection in cattle is usually seen in reduced milk yields, lower liveweight gains and in liver condemnations in the abattoir.

There is also strong evidence that fluke can act as a trigger for other problems, such as clostridial diseases. In sheep, severe cases can result in death.

“If a sheep dies, take it for post mortem – it is easy to rule in or rule out fluke as the cause,” advises Dr Skuce.

When it comes to treating cattle or sheep for fluke, he maintains that farmers must start to talk about the active ingredients or chemicals contained within the different fluke products, not just the product names. As shown in Table 1, a number of chemicals only kill adult fluke, while others kill fluke from six to eight weeks.

Only Triclabendazole given orally will kill the early immature stages, down to about two days in sheep and two weeks in cattle (eg Fasinex). However, these products have been used extensively in local sheep flocks, and there is growing evidence of fluke resistance to this drug.

“Care should be taken when using Triclabendazole – use it when no other option is suitable, and as part of an overall strategy discussed with your vet,” suggests Dr Skuce.

As well as killing fluke at different stages of maturity, it is also important to note that various products have different meat and milk withdrawal periods, with a number not licensed at all for use in lactating dairy cattle.

When administering a dose, calibrate equipment to ensure that the product is administered accurately. Under-dosing leaves parasites in the animal, causing damage to the liver and is known to select strongly for drug resistance.

In February 2011, the European Commission initiated an investigation into the various chemicals used to control fluke in dairy cattle and their respective withdrawal periods.

By late 2012, they had concluded that changes were required in product information, which has resulted in a number of flukicides no longer being recommended for use in lactating cows because of concerns about chemical residues getting into the milk supply chain. This includes products which contain Closantel (eg Closamectin, Flukiver), Nitroxynil (Trodax), Triclabendazole (eg Fasinex, Tribex) Clorsulon (Ivomec Super) or Oxyclozanide in combination with Levamisole (eg Levafas Diamond).

In some cases, there are authorisations in place to allow products to be used in pregnant maiden dairy heifers and in far-off dry cows. Advice should be sought from your vet or a suitably qualified professional before putting a control programme in place.

The change in the rules means that most dairy producers are limited to products containing Albendazole, which has a 60-hour milk withdrawal (eg Albex, Endospec and Ovispec) or Oxyclozanide (Zanil), with a milk withdrawal period of 72 hours.

Given that both chemicals only kill the mature stage of fluke, a two-dose programme approximately eight weeks apart is typically required.

In practice, this probably means dosing cows at drying off and again at calving.

Containment

Dairy farmers who operate containment systems are obviously at a much lower risk of liver fluke.

However, according to Philip Skuce, there is still a need to monitor fluke levels in cattle.

“There can be some gaps in the system; for example, a lame cow let out to a paddock or where fresh grass is fed to cows. In housed systems, monitor rather than treat in the first instance,” he maintains.

Rumen fluke eggs started to appear in dung samples taken from British and Irish cattle in the late 2000s and recent analysis from AFBI has suggested that around 30% of sheep and 40% of cattle in NI now have rumen fluke.

To date, the clinical importance of rumen fluke is still under debate, although there is plenty of anecdotal evidence from farmers that treatment has been followed by improved animal performance.

Generally, mature adult rumen fluke on the surface of the rumen do not cause clinical disease. Problems such as ill-thrift or diarrhoea are thought to be caused by large numbers of immature rumen fluke clamping onto the wall of the intestine.

“If there are large numbers of immature rumen fluke in the intestine, it must be assumed that they are doing some damage. In such cases, it would make sense to treat them,” maintains Philip Skuce.

Recent studies have shown that rumen fluke in British and Irish livestock are the same species as identified on mainland Europe. This European species of rumen fluke is understood to favour the same mud snail used by liver fluke as its intermediate host.

The life cycle of both rumen and liver fluke is similar.

The precise species of snail infected with rumen fluke in Britain and Ireland has yet to be determined. Farmers who think they have a problem with rumen fluke can take a dung sample along to their local vet for analysis – the test is the same as for liver fluke.

Rumen fluke is controlled using Oxyclozanide-based products (ie Levafas Diamond or Zanil).

The overuse of Triclabendazole-based products to control liver fluke has resulted in resistance being reported in a number of parts of Britain and Ireland. “We don’t know just how much resistance is out there. It is difficult to measure fluke resistance, but we are dealing with a complex, genetically diverse parasite and treating every month with the same chemical is not sustainable,” says Philip Skuce.

His advice for sheep producers is to vary chemicals strategically throughout the season, for example, using Triclabendazole (eg Fasinex) in the autumn, followed by Closantel- and Nitroxynil-based products (eg Flukiver and Trodax, respectively) in the early winter and adulticides like Albendazole and Oxyclozanide in the late winter/spring, again in discussion with a local vet or suitably qualified professional.

In all cases, it is worth testing the efficacy of the products used using a faecal egg count reduction test – your vet will be able to advise.