In the whole of 2010, the cash loss in England, Scotland and Wales due to sheep livers condemned for fluke infestation was just over £1 million (£1,040,213) at current market values less pet food realisation, according to Dr Phil Hadley from Eblex. He says this is based on Food Standards Agency data that 7.23% of sheep livers—995,419 in number—were rejected for fluke.
If the impact of fluke on sheep performance was also taken into account, the loss would be considerably larger, adds Pfizer vet Andrew Montgomery. "The majority of disease outbreaks are seen in early/mid-winter due to ingestion of infective cysts shed onto pasture late summer through to early winter," he says. "However, finishing lambs may not show clinical signs of acute fluke, yet the FSA figures prove that a significant number are carrying sufficient fluke at slaughter for their livers to be condemned.
Dealing effectively with fluke requires an understanding of its life-cycle. Sheep ingest infective cysts off pasture and they develop through early immature then late immature stages before maturing into egg-laying adults. The significance of these stages is in choice of flukicide, because some kill adults only (e.g. clorsulon), others will kill late immature and adults (e.g. closantel, nitroxynil) while only triclabendazole kills all three.
Where liver fluke is a known threat, Mr Montgomery advises a triclabendazole-based treatment in the autumn to ensure that all life-cycle stages including early immature are killed, thereby reducing the risk of acute fluke disease. Otherwise, he cautions that an autumn flukicide that doesn’t kill the early immature stage can allow them to develop into adults during the following two to three months, potentially causing acute liver damage or the impaired growth rates associated with chronic fluke disease.
"In ewes and lambs alike, it is crucial that an autumn fluke treatment kills the early immature stages," he says. "If a mixed infestation of worms and fluke is being treated, then a single-dose treatment of moxidectin-triclabendazole is appropriate."
An important issue in fluke control is the occurrence of suspected triclabendazole-resistant fluke. On investigation, Andrew Montgomery reports that treatment failures are usually due to factors other than resistance. For suspected cases of triclabendazole resistance, he says Pfizer’s team of field-based livestock vets is available to investigate, identify the scale of the problem, and promote better management practice.
Lamb fatalities halved following change in fluke and worm treatment
Liver fluke had become a perennial and known enemy for GH Davies Farms Ltd—an 800-hectare arable, beef finishing and sheep business—at Green Farm, Condover, near Shrewsbury. Jim Davies, farm partner responsible for the sheep enterprise, recounts fatalities in hogs (store lambs) in the past, with VI Centre investigations confirming fluke as the cause. Abattoir feedback about damaged livers in slaughtered lambs provided more evidence. With grazing near watercourses and buying-in from unknown sources, the farm is a likely candidate for fluke risk in the absence of effective defences.
A lambing flock of 300 ewes and finishing between 8,000 and 10,000 store lambs each year means there is a substantial investment to be protected, according to Mr Davies. "The stores are bought in local markets then batched into management groups of 500, to clear up autumn grass first before moving onto stubble turnips," he explains. "Some creep feed is also used to push later lambs towards finish."
On arrival, store lambs used to be dosed with triclabendazole flukicide and an injectable, non-persistent, worm and scab treatment. However, during 2007 to 2009, Mr Davies says he became "disappointed with the worm cover we were getting". In 2010, this concern that parasite control was less effective than it should be prompted the change to a combination moxidectin-triclabendazole drench (trade name, CYDECTIN® TriclaMox®) for worms and fluke, and contractor-operated dipping for sheep scab.
Over the 2010-11 winter, Mr Davies reports that lamb losses due to worm-related scour were halved compared with previous years and in finished lambs sold deadweight, there was no feedback about damaged livers from the abattoir.
