7 May 1999

AS RESILIENT AS FLOCKS

Theres been much talk in the sheep industry recently about the need for producers to cut costs if they are to stay in business. This may be true but the sheep industry has survived for many centuries in good and bad times, when many other industries have fallen by the wayside.

This is a testament to the industrys strength and those that work within it. Flockmasters throughout the country have weathered turbulent times before and are just as resilient as the sheep they keep.

No doubt there will be new challenges ahead, and despite the harsh economic climate, when financial problems take priority, issues must be dealt with and not put on the back-burner.

Scrapie is one of these. SEACs recent report on transmissible spongiform encephalopathy (TSE) called for scrapie to be eradicated from the national flock.

Fortunately the sheep industry has learned lessons from BSE and has been proactive. In this Update, we look at findings from the on-going scrapie study at the Institute of Animal Health to see what more flockmasters can do.

And, as the lamb selling season approaches we look at ways to boost returns by improving carcass weights, while one Essex producer discusses the benefits of using high-index rams.

But it is not only rams that are important: Breeding ewe prices tumbled last year but many old ewes were kept because of poor trade. One consultant in this Update examines this policy, revealing how important it is for production and profits to rigorously cull old ewes and maintain a young, healthy flock.

SCRAPIE OFFENSIVE WELL UNDER WAY

Scrapie has perceived links

with BSE, but is also a

terrible, debilitating disease

that ultimately leads to

death. James Garner reports

POSITIVE steps are being taken within the sheep industry by breeders and scientists to address scrapie and the best ways to control it.

A study at the Oxon-based Institute of Animal Health, Compton, should give flockmasters more information about how the disease spreads within flocks, what the best methods of control are and how the environment affects its transmission.

Last year, a four-year comparative study began with the help of 60 producers. So far researchers have taken blood samples from 4,255 sheep. Each sample is genotyped for scrapie susceptibilty.

Researchers aim to understand the different strains of scrapie and whether the best method of control is breeding scrapie resistant sheep or if a change in farm practices would prevent transmission between animals?

But it isnt an easy disease to study, says Matthew Baylis, senior research officer at Compton. "Because its not a virus, but is carried by prions, which are proteins that occasionally mutate, there were no laboratory tools to study the disease. These are appearing now as our research develops."

The IAH scheme works by matching flocks to compare similar numbers of sheep of one breed that have the disease with those that dont.

Blood tests are taken from the whole flock – up to 400 sheep – genotypes are looked at and breeding decisions monitored. "Flockowners in the trial have to inform both IAH and MAFF of any cases of scrapie, so we can investigate the animal."

To examine what causes scrapie the IAH needs to know which breeding decisions are taken and therefore animals need to be individually identified. By examining these cases, researchers hope to identify the best ways of controlling the disease and whether current genotyping procedures are adequate.

Currently, genotyping varies between breeds. This is based on past genotyping patterns where different breeds have shown variations in genotypic susceptibility at different codons, says Mr Baylis.

"We will be looking at all the sites from 136 to 171, the current range, but were not expecting there to be any difference to current genotyping patterns."

The variation in susceptibility between different breeds, and similarly the variation in which codons need to be genotyped, is down to chance, says Mr Baylis.

"Its down to the founding affect, when breeds were developed the animals they came from happened to have resistant genotypes. This sets the genotypes for their descendants."

Despite a successful start, the IAH would still like to have more scrapie infected flocks to study.

But as there were only 400 reported cases of scrapie last year there are many more flocks without the disease than with it.

However, this probably doesnt portray the full picture, says veterinary officer Fiona Houston.

It could reflect a significant level of under-reporting, she says. "But also some animals carrying the disease die before they develop symptoms while others will be slaughtered long before scrapie develops.

"Scrapie takes at least 18 months to develop in lambs when contracted at birth. It begins in the tonsils, moves to the gut and spleen before infecting the immune system and finally the brain, when symptoms are finally shown.

"In most cases sheep are over two years old, but the incubation period varies. Once symptoms develop it normally takes two-three months before death, although it can be quicker," she says.

Infected animals normally develop discoloured brown or yellow wool which feels greasy. They also isolate themselves, lose condition, become unco-ordinated, scratch a lot and appear nervous.

Although the best methods of control seem to be through breeding, because there is no vaccine, Mr Baylis says the environment probably helps transfer disease.

"Infected sheep are incubating the disease for some time before dying, so they have already passed on the infection."

Indications suggest that lambing time is one period where transfer occurs. "Lambs born to infected ewes are exposed to large amounts of the prion in the afterbirth. If they are a susceptible genotype they will develop scrapie later."

Disinfecting shared lambing pens between ewes could lower the risk of transfer between animals, says Mr Baylis.

But there are other areas that could be involved in disease spread, he says. Hay mites in supplementary feed, the prion surviving in certain soil types, or being passed on by rams during mating are all potential concerns, says Mr Baylis.

Producers in the study have their whole flock genotyped free of charge and will be given their genotypes when the study ends. They will get some information during the study, but probably not all of it otherwise there would be unfair comparisons if they change their breeding decisions, says Mr Baylis.

"However, we know that having this information is a good selling point for sheep breeders."

Any flocks interested in participating should contact Matthew Baylis. The IAH is interested in flocks with scrapie, and flocks willing to be genotyped but not privy to the information. &#42

Matthew Baylis (01635 577282).

KEEP TUPS IN TRIM AND PROTECT INVESTMENTS

HIGH-INDEX tups are expensive animals to purchase. Looking after them during winter and before next seasons tupping will protect your investment.

Nick Fredericks and brother Chris run 312 February lambing Mule ewes at Temple Farm, Roydon, Herts. They also have arable crops and free range turkeys and chickens.

They purchase two shearling tups every year from a local sire reference scheme pedigree Texel breeder, says Nick Fredericks. "We run eight tups with ewes for six weeks in mid September."

But Chris says that they are lucky to have a local supplier of high-index rams which makes for a good arrangement on both sides.

"We have been told by advisors that fast growing Texels are as good as any other terminal sire breed. So we look for good growth rate figures as well as a high overall index. Growth rate is particularly important because we want most lambs slaughtered by early July before harvest starts."

However, rams arent selected on figures alone, says Nick. "I pick out the tups I like and then we compare their figures to make the final choice."

But it is partly because of the pedigree breeding that tups need looking after to ensure value for money, says Nick. "We notice that our teasers always live two years longer than tups because of their hybrid vigour.

"Youre investing a lot of money, so its worth taking care of them. We regularly check ewe condition, so why should tups be different?"

Checking on tup condition continues all year, says Chris. "We always make sure they have plenty of keep and will feed them, when required, before tupping."

Turkeys occupy buildings at Temple Farm before Christmas, so tups are not housed until some shed space has been cleared. "After Christmas theres little goodness in the grass, so we bring them indoors where its easier to keep an eye on them," says Nick.

Once housed, tups are fed ad lib silage and 0.5kg/head/day of 17% protein home-mix concentrate consisting of 30% wheat, 30% barley, 20% sugar beet pulp and 20% protein balancer.

To ensure their general health is maintained, tups are part of general flock health treatments. "We worm the tups at turnout and again before tupping."

Tups also receive an annual vaccination for pasteurella and clostridial diseases and might soon become part of a foot-rot vaccination scheme along with the bought-in replacement shearling ewes.

This is because tups seem to be more susceptible to foot-rot but must be good on their feet during tupping, says Chris. "In productivity terms, injecting one ram is equivalent to treating 40 ewes at tupping time."

Ensuring tups are without stress and that their ability to mate is not hindered continues throughout the year. Rams tup ewes without a raddle otherwise they develop a sore brisket.

"This is taking a bit of a risk in case one tup is infertile but judging by our scanning figures of 222% theres little to worry about," says Nick. &#42

Tups are twice as susceptible as ewes to disease, says SACs John Vipond, so its important to check on their condition throughout the year.

"Begin getting tups ready for mating 12 weeks before you need them. For early lambing flocks that means starting now."

He suggests giving routine injections for pasteurella and clostridial diseases, worming regularly and to their correct weight. When tups are in poor condition feed sugar beet pulp at 0.5kg/head/day. And a long acting injection of selenium may improve fertility.

TUPCARE

&#8226 Sire reference scheme tups.

&#8226 All year care.

&#8226 Feed in winter.