15 January 1999

Scrapie resistance is target for Norfolk unit

By James Garner

AN AMBITIOUS scheme to breed a flock of scrapie-resistant sheep as quickly as possible is underway in one Norfolk pedigree sheep flock.

The programme uses DNA genotyping and embryo transfer and is expensive – costing £100/lamb born. However, Jonathan Barber who jointly runs 200 pedigree Charollais ewes and 150 Merinos with wife Carroll at Crogham Farm, Wymondham, Norfolk, believes the projects long-term aim is worthwhile.

"Were on a fast-track scheme to breeding a flock of scrapie resistant sheep which is why large numbers of sheep are involved.

"Its a question of reacting to consumer perception about scrapie. As the technology is there, why not use it and remove that particular consumer concern?

"It will take four to five years for the flock to become fully scrapie resistant using embryo transfer," says Mr Barber.

Because they are using embryo transfer the Barbers only require a small number of ewes with genotypes for scrapie resistance to flush eggs from. This means its possible to combine scrapie resistance and genetic improvement.

Breeding for scrapie resistance is often believed to reduce the flock gene pool by selecting ewes and rams from the same bloodlines. But in this case Mrs Barber is convinced its not to the detriment of the flock.

"We would have stopped if we hadnt sufficient bloodlines, and by selecting ewes carefully the flocks genetic progress is not jeopardised," she says.

"We selected 100 Charollais ewes, all older than two shear, to scrapie genotype in March. All ewes had lambed before and so were proven performers. From them we were able to select 20 ewes with good resistance to scrapie, high indexes and type to flush."

Three-quarters of ewes flushed were RR genotype, so were least susceptible to scrapie, with the remaining quarter RQ/AA, the next least susceptible genotype.

The selected Charollais ewes were sponged and then given an injection of follicle-stimulating hormone to encourage super-ovulation. "Instead of shedding one egg, donor ewes shed 10 to 40 eggs in the uterus. They are fertilised using laprascopic artificial insemination using semen from RR genotyped high-index rams.

"Eggs are then flushed from the uterus by surgical operation at day four to five and examined under a microscope to identify quality and how many eggs are fertilised, which varies from none to 40. This year we averaged 13 embryos a ewe," says Mrs Barber.

Having established quality and number of embryos to transfer,the Barbers chose recipient ewes. The Merino and Merino cross ewes selected have a high health status, and must be Maedi Visna accredited and scrapie monitored to protect lamb health status.

Other factors are also important says Mrs Barber. "Early lambing ewes must have enough frame to allow lamb growth in the womb. They should also milk well to feed fast growing lambs."

Normally recipient ewes will be two shear or older but this year, because of high embryo numbers, shearling Merino ewes were used.

But theres no guarantee of embryo numbers, and so Mr Barber feels that its important producers decide how many embryos they can afford. "Extra embryos should be thrown away or frozen to keep costs down, but freezing embryos can mean losing up to 40%."

The 96 recipient ewes lambed in early December, but this years embryo transfer results were below average says Mrs Barber, who would expect 70% of transfers to be successful. This year the Barbers managed 60% and 154 lambs were born but the programme is still worthwhile, she says. "They are our best genetic material, and half will be ram lambs which will be sold.

"Additionally, embryo transfer allows us to identify good breeding ewes in a short time. Normally you would have six lamb crops in six years, but with embryo transfer you have six lamb crops from a single ewe in one year, so you can compare lambs and see whether to use that ewe again."

Its also a good method to establish how reliable a sire is, says Mr Barber. "Some high-index sires show a variation in lamb quality and indexes."

Mr Barber feels that a fast-track scheme producing scrapie resistant stock may be an attractive option for other pedigree breeders.

"It is a way to quickly remove another breeding concern, so you no longer need worry what genotype your best lambs are and that they might not be suitable to sell to some buyers."

– ET/Scrapie program.

DNA genotype ewes and sires.

Costs about £100/lamb.

High health status recipients.

ET/SCRAPIEPROGRAMME

&#8226 DNA genotype ewes and sires.

&#8226 Costs about £100/lamb.

&#8226 High health status recipients.