Sheep farms suffer as the worms turn

Published on Thursday 5 February 2009 21:37

SHEEP numbers are declining on the international front as producers switch to arable or beef and dairy production, but there are still hundreds of millions around the world.

Farming sheep remains a major industry in Europe, and the UK is the largest producer, with the national output of sheep meat forecast to be about one million tonnes this year.

Profitability has in most countries improved in recent months, but sheep farmers everywhere are facing an increasingly common problem: resistance to the drenches used to control gut parasites, principally nematodes, or roundworms.

Farmers are finding that many of the drugs used to control parasites are much less effective than in the past, as the worms are mutating – and new treatments can take about 20 years to develop.

The issue was discussed in Edinburgh this week at a conference attended by delegates from around the world. It was part of the international "Parasol", or parasite solutions, project, funded by the EU.

Dr Frank Jackson is part of a team at the Edinburgh-based Moredun Research Institute that has been investigating this issue.

He said: "The last few years have seen changes in the climate which have led to increased parasite numbers and thus increased the risk of roundworm disease."

In recent surveys Moredun has discovered that six out of ten farms have resistance of varying degrees to the commonly used so-called white drenches. In addition a third of units have shown resistance to the clear drenches. Worse still, some farms have demonstrated a multiple resistance to all three of the commonly used products.

Farmers are partly to blame for this situation in that they routinely dose all their lambs at various times of the year even if there are no signs of clinical symptoms. The current veterinary advice is not to dose unless strictly necessary. This, said Mr Jackson, is known as "targeted selective treatment" or TST, as opposed to "targeted treatment", or TT, when the entire flock is treated.

Mr Jackson said: "The TST route has been successful in South Africa in helping small farmers who were teetering on the brink of poverty. Their wool yields have improved considerably. The TST approach looks to be the best option and here in the UK trials on eight farms have resulted in average savings on drugs of 663 per year."

However, the difficulty, particularly in the Scottish and Welsh context as well as in Australasia, is a lot of work would be involved in the handling of large flocks.

Another possibility, but one fraught with difficulties, is the reintroduction of genes susceptible to current drenches in the worm population. This has been achieved in trials, but would be problematical on a farm-scale basis. In the short-term, farmers will be better to adopt a pragmatic angle and where possible avoid blanket dosing which clearly is a root cause of product resistance.