SCRAPIENOTTHE ONLYISSUE
19 February 1999
SCRAPIENOTTHE ONLYISSUE
Northern breeders are
making significant in-roads
to breeding for resistance
to scrapie in Swaledales. Jeremy Hunt reports
BREEDING for scrapie resistance is a key for Swaledale supporters, but it shouldnt be at the expense of other production traits.
Lancs Swaledale breeder Tom Robinson is fully committed to the breed societys voluntary scrapie testing scheme, but he believes a balanced approach to the selection of tups will ensure a sound future for the breed as a strong hill sheep. This should take account of both genotyping and breed characteristics.
Despite a slump in hill farm incomes, commercial flock owners buying tups at the breed associations sales last year were prepared to pay a premium for rams with a high level of scrapie resistance, justifying breeders persistence.
The Robinson family run about 2800 Swaledale ewes on two hill farms – Catlow Farm and Sykes Farm – extending to 2430ha (6000 acres) deep in the Trough of Bowland near Slaidburn. About 2000 are bred pure; the rest are crossed with the Blue-faced Leicester.
Mr Robinson, a member of the Swaledale Sheep Breeders Assoc-iation council, explains: "We started testing for scrapie as soon as we could just for our own benefit and to help us with our breeding and selection.
"Now, like many other flocks, we are seeing the benefits. We have been using high-resistance tups for several years which meant that last autumn we could be more flexible. On breeding and conformation the tups we bought this year had genotyping C1 and C2; because of the high resistance tups we now have behind us we could buy them confidently.
"My own opinion is that breeders should not aim solely for the tups classifying as A and B under the test just because of the high resistance to scrapie.
"You need a broad spectrum of genes to retain the Swaledales characteristics of vigour, milk and hardiness. The breeds traits passed on through the Mule play its part in commercial prime lamb industry and that must not be totally compromised.
"There has to be a degree of flexibility particularly as breeders now have so much more information upon which to base their flock breeding plans," says Mr Robinson.
Prior to the official start of the SSBA scheme, the Robinsons independent testing had revealed that two five-figure bought-in stock tups, of which they were part owners, tested D for scrapie resistance.
Selective culling of the progeny of these rams was undertaken followed by the use of A and B1 tested rams on those that were retained. Subsequent testing of the next generation produced A, B and C progeny with only a couple of rams testing C3.
"All we can do is follow the advice that is being given to us by MAFF. Genetics is not an exact science, but the scheme is certainly enabling Swaledale breeders to eliminate those genes which pose the highest scrapie risk.
"I believe scrapie had pretty well been eliminated from most flocks by the time official testing started. Tagging and recording had enabled breeders to do a great deal themselves, but because the breed had scrapie in the past there was a stigma that we had to officially off-load."
Mr Robinson says the long-term benefit will be to reduce the amount of genetic material in the breed that could increase susceptibility to scrapie. If valine is present in the gene it can, although not always, be the scrapie trigger.
Rams which test B3, C4 and D all carry the valine gene. D rams have never been accepted for breeding, but now as the scheme progresses C4 and B3 have been removed on MAFFs recommendation.
Over the last two years the Robinsons have tested 60 shearling rams which have produced only three D tests. "I am aiming to have a mix of rams from the approved scrapie test classification to maintain a broad spread of genetic material in the flock. We will not simply buy a ram on its test result. We select a tup and then look at its test."
Spring-born ram lambs retained as potential shearlings for forthcoming autumn sales are tested from the following January. This year around 45 rams will be blood tested by a vet. Breeders are charged £40 a test plus the veterinary fees.
Breeders receive official documentation concerning the test results and a certificate is given to each ram denoting registration details and its scrapie genotyping.
Catalogue details of rams offered at official breed association sales include details of the animals genotyping; breeders were pleased that last autumn, despite low prices, commercial ram buyers paid a modest premium for B1 and C1 sires.
Experienced Swaledale breeders, now several years down the road of testing and with a broad picture of the genotyping status of their flock, were still prepared to pay good prices for superior C3 sires.
"We are now getting to the stage with our tup hoggs that we can almost predict their genotype because we are building up so much information about the parents and grandparents."
But breeders within the scheme remain concerned about the risk of eliminating genes from the breed which may also carry valuable traits. "At the back all our minds we are always conscious about narrowing the genetic pool. Tups genotyping B3 and C4 indicate the presence of valine. Thats what the experts tell us we have to eliminate but do we really know enough about it?" asks Mr Robinson.
"But presumably there will still be some valine left in the gene pool of the females. We would be able to tap into that if there was ever a change of thinking on the way we have approached the control of scrapie.
"Some breeds chose to take all valine genes out as a priority. The SSBA elected to do it more gradually removing D and then B3 and C4s."
This season the Robinsons are using one A, five B1, four B2 and three C1 tups. Around 1400 ewes have been hand-picked to run with specific tups.
"The matching of ewes to tups aims to achieve a balance. Breeding for the best looking sheep maintaining all the characteristics of the Swaledale is very important, but we then have to factor in the genotyping. If we have a ewe by a C3 tup we would not run her with a C3; we would aim for a C1, a B1 or a B2."
In the long term he believes the scheme will have far reaching benefits across the sheep sector.
"If this scheme is whats needed to ensure the sector does not find itself facing the same animal health crisis that has ravaged the beef industry, then it must be worthwhile and particularly when you consider the importance of the export trade." *
BREEDINGGROUPS
THE SSBA scrapie gene test scheme only allows sheep that are found to be resistant to the disease to be used for breeding. Animals are now being classified in three groups – A, B and C – and subdivided within those groups depending upon their genotype.
Class A indicates a high level of resistance and a high level of protection in any progeny. Sheep with Class B and C results also generally have a high level of resistance in the Swaledale breed but progeny of Class C stock may be less protected than progeny of Class B sheep.
The current scrapie gene test classifications are: A, B1, B2, C1, C2 and C3.
SCRAPIE RESISTANCE
• Voluntary testing widespread
• Selective breeding for resistance
• Mustnt limit positive traits
• Resistant progeny get premiums