Genotyping
Scrapie can be difficult to control and methods commonly employed include the selective culling of infected flocks or family lines, prompt removal of afterbirths from lambing pens and the use of "genotyping" technology.
Scrapie develops when the normal form of the PrP protein in a sheep's brain converts to an abnormal form. The PrP gene which produces this PrP protein also determines a sheep's resistance or susceptibility to scrapie i.e. whether or not it is likely to develop scrapie in its lifetime if exposed to the infectious agent.
The sheep PrP gene has two copies (or alleles), one derived from each parent. An animal that has inherited the same information on the alleles from both of its parents is said to be a homozygous genotype (e.g. ARR/ARR, AHQ/AHQ). If it has inherited different information it is said to be a heterozygous genotype (e.g. ARR/ARQ).
Taking the homozygous or heterozygous pairing of alleles inherited from both parents into account allows for the generation of up to 15 different genotypes. Some breeds are known to contain all 15.
Scrapie resistant sheep can be used in a breeding programme to confer resistance to their progeny and, over time, this will impact on the incidence of disease in the national flock.
The Predicting Method Chart (201 KB) illustrates the principle of how genotypes can be predicted in progeny.
If you know the genotypes of your ram and ewe, you can use the Genotype Calculator Grid (74 KB) to work out the possible genotype outcomes of their offspring.