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Increasing fluke problem made worse by resistance

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Liver fluke is probably one of the biggest problems facing the livestock sector at the present time, according to Scottish upland sheep and suckler cow producer Neil Gourlay. Neil, who farms at Moniaive in Dumfries, says he believes that fluke generally is an increasing problem, and that resistance to certain products is adding to this.

Neil's family have been farming in Dumfries since 1953 and he is the third generation to run the farm. They now have four units within a five mile radius producing Charolais calves to sell at a year old, and finished lambs and sheep for the marketplace. Across the units they have between 400 and 450 suckler cows and around 3,200 breeding ewes.

Neil says that the last twelve months have probably been one of the most horrific periods he has experienced in livestock. "For those of us in this region and I am sure for many other areas too," he says, "The lack of sunshine and wet days last summer, the poor fodder that was made for the winter, and the tough winter have made it really difficult. Then just at the start of lambing time in March, there was the snow that killed hundreds of sheep."

All of which has added to a rising problem with liver fluke. "Over the last few years we have seen the climate become considerably wetter, and this has led to a major increase in fluke infestation in the cattle and sheep. Three or four years ago we used to dose the ewes for fluke once or maybe twice through the winter periods. It has got to the stage now where we have to treat the sheep around every four weeks throughout the winter," says Neil.

"On the cattle side, they are much poorer coming into the sheds for the winter, and we need to treat them immediately at housing.

"Overall, fluke is much more of a problem in this region. Talking to other people in the industry, mainly locally in south Scotland, there are clearly increased problems with incidences of fluke and with resistance to certain products. Even in places on the east coast, where fluke normally was not too much of a problem, they have been having serious issues with the parasite."

On Neil's farm they have had a particular problem with triclabendazole resistance. Based on its efficacy against early immature fluke, those stages that can often cause death in sheep, triclabendazole is the product that they used most. Three years ago, they did their normal autumn pre-tupping dose for fluke, but within three weeks discovered that one of their flocks was still infested with fluke.

Neil says: "We couldn't believe that the sheep had become re-infested with fluke, having been treated only three weeks previously. What we then uncovered with the help of the SAC and the local vets was that we had resistance to triclabendazole. The more I looked into it the more I discovered that this was much more prevalent than we had been led to believe.

"It was very disconcerting to discover that the product was not working, and to have to bear the associated costs. Because it kills the immature fluke, we had routinely used triclabendazole and I suspect that this over-use has resulted in the resistance problem.

"Once we uncovered the problem we had to work with local vets and the SAC to develop a revised treatment regime. This involved rotating the use of other flukicide actives to help ensure that we didn't get further resistance and that we kept the flock as free of fluke as possible. However, because triclabendazole is the only product that is effective against early immature fluke, it is a problem. We can't take the sheep off the pasture, so you never get rid of the fluke."

Talking to other livestock farmers in the region leads Neil to think that triclabendazole resistance is quite a widespread problem. He believes that they relied too much on the product, and recommends that those farmers who do not currently have a resistance problem should ensure that they review their treatment regime and do not over-use it; conserve treatment to the times of year when new infections from the pasture are high.

"Having a rotation strategy, and using triclabendazole at the right time as part of that, is the way to ensure that you don't end up with the kind of resistance that we have," he says, "Because we now have this resistance we urgently need another solution for treating early immature fluke."

As far back as 2010 experts such as Dr. Theo De Waal BVSc, PhD, Senior Lecturer at the School of Agriculture, Food Science and Veterinary Medicine at University College Dublin, were warning about the problems of over-using triclabendazole, and preserving it for use against early immature fluke in sheep.

Fiona MacGillivray, Veterinary Adviser with Merial Animal Health, says "Currently the only reported cases of flukicide resistance have been to triclabendazole. The trend towards wetter and warmer weather favours the fluke life-cycle and as such we are seeing increased risk from this parasite.  Cattle rarely suffer from acute fluke disease caused by the early immature stages of the parasite, whereas sheep are at much higher risk.  As it is the same parasite that infects both cattle and sheep, in order to ensure farmers retain the ability to use triclabendazole on their farms they should certainly consider treating their cattle with an alternative flukicide to triclabendazole, to avoid over exposure to this active."

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