18 February 2000

THERIGHT STRATEGY FOR SCRAPIE?

Scrapie genotyping is

becoming common practice

among pedigree flocks.

But is the industry tackling

scrapie in the right way?

James Garner investigates

WHEN BSE broke into the public domain in 1996, many sheep breeders believed its connection with scrapie would bring the sheep industry to the floor as well.

This has not turned out to be the case, but many breeders are working hard to increase their own flocks resistance to the disease.

NSA chief-executive John Thorley believes scrapie eradication in the UK is unrealistic. Nevertheless, he is encouraged with the uptake of scrapie genotyping by breeders and their endeavour to find out more about the disease.

Uptake of blood testing has been helped by SAC cutting costs to make its genotyping service competitive with US tests. This has been a priority, says Brian Hosie, assistant head of SAC Vet Centre, Edinburgh.

Prices had to come down, says Charollais sire reference scheme chief-executive Jonathan Barber. "It was a commercial situation. If SAC wanted to test any quantity of sheep in the UK, its costs had to come down. Genecheck in the US helped drive prices down."

Despite costs coming down, prices differ from breed to breed depending on the complexity of the test. Because testing some breeds is more complicated and takes more work it is more expensive, says Mr Hosie.

"We have been hell bent on driving down the costs of testing, but we cant subsidise one breed of sheep by charging another more money."

Breeds do vary considerably in their complexity with Suffolks at one end of the scale, being relatively easy to genotype, and Texels at the other end being fairly complex because they have more variations within the genotype.

Interest among sheep breeders in genotyping is helping to build information about scrapie and its susceptibility in certain breeds, alongside information that has been accumulated from abroad, says Mr Hosie.

Despite this progress, risk categories will remain under review. Currently, sheep that have been genotyped carry a risk rating which indicates their susceptibility.

There have been criticisms from some breeders that these results and risk ratings are inaccurate and re-testing often shows a different result. Defending the test, Suffolk sire reference scheme secretary David Hiam says that in his experience it is often the animals pedigree that has been mis-read, rather than a wrong blood test.

Mr Barber agrees: "Ive heard stories of people being unsatisfied, but you cant blame testing – often its because the animals havent been identified properly or the blood may have been packaged wrongly. Theres more chance of human error than incorrect results."

One remaining problem is that pedigree sheep breeders have yet to see returns from their investment in scrapie testing, says Mr Thorley. "Ideally we want to be in a situation where sheep breeders are developing a high level of resistance in their flocks."

This can be transferred to the commercial market by a cascade effect, he says. "Commercial flocks can pick up scrapie resistance in their flocks through tups they purchase."

Mr Barber says this is happening. "There are some commercial flockmasters who look for scrapie genotyped tups, but they may not want to pay more for them.

"This is either because they have had a scrapie problem in their flocks, which they can reduce by buying rams of the right genotype, or they have decided to move in that direction because processors or retailers have hinted that they should."

Texel chief-executive Steven McLean is not so sure about commercial demand. "But if pedigree breeders are resolving the issue in their flocks, does it really matter about commercial demand?" In other words, scrapie resistance should filter down to commercial flocks regardless.

As with most breeds, Texel breeders are tackling scrapie by blood testing stock rams and replacement ewe hoggs, says Mr McLean. "R1, R2 and R3 tups are being used, while R5 rams are being discounted.

"I dont think the risk categories are clear, and in fairness it is a difficult concept to grasp, but I think breeders know what not to use."

Scrapie eradication may be unrealistic, says John Thorley, but he hopes commercial flocks will develop resistance by purchasing scrapie resistant tups.

GENOTYPING

&#8226 Drop in price of UK tests.

&#8226 Accurate results.

&#8226 Resistance will spread to commercial flocks.