Scrapie resistance

The Goat Improvement Company currently provides the option for semen selection from Grasshill bucks categorized with varying levels of genetic resistance to scrapie. This  labelling is determined by DNA testing at Trent University in Ontario, Canada to confirm the existence or absence of the ‘scrapie resistant’ glutamine (Q) codon at variant position 211 of the prion protein gene (PRNP). It is quite important to note that although the basis for this testing was research by Trent into various DNA sequence variations which identified the Q glutamine at position 211 as the indicator most likely to provide scrapie resistance, this finding has yet to be validated by OIE, and plans for challenge testing to confirm validity are currently underway. As such, no guarantees are made by Grasshill as to the scrapie status of offspring resulting from breedings to sires DNA identified as Homozygous or Heterozygous scrapie resistant based on the existence of this codon. Evidence from the research which initially resulted in the discovery of this ‘scrapie resistant’ Q glutamine at position 211 though, strongly supports its resistance properties, and it is up to individual breeders to decide how much or little they wish to utilize a buck’s rating based on the existence of this resistant codon as a selection tool for minimizing the potential existence of scrapie in their herd.

What does that mean for you as a dairygoat farmer?

  • Selectively breeding for animals who carry genetic scrapie resistance is one of the best tools for minimizing the incidence of this disease in your herd.
  • Selective breeding in animals that have genetic resistance to scrapie is one of the best tools to minimize the incidence of this disease in your herd.
  • Although the OIE has not yet officially recognized the scrapie resistance properties of the Q glutamine at position 211 identified by Trent University (and no guarantees can be made as to these properties until this validation process is complete), researchers still see great potential in selective breeding strategies aimed at reducing the incidence of scrapie in a herd by maximizing the incidence of this scrapie resistant codon.

Bucks identified as ‘homozygous scrapie resistant’ based on the double existence of this gene, will certainly transmit at least one of these genes to each of their offspring (even if the dams themselves have no genetic scrapie resistance). Which should then presumably provide a significant level of resistance to these heterozygous animals (although more testing is required to accurately predict this level). Offspring from goats bred to heterozygous bucks possessing only one scrapie resistant gene, may receive either one scrapie resistant gene (also giving them significant scrapie resistance) or none of these genes, (providing no extra resistance). Which would definitely be the case in the offspring of all goats bred to a buck not possessing the scrapie resistant gene if the females bred also lacked this gene. Obviously the offspring most likely to inherit scrapie resistance are those resulting from parents who both carry this gene (especially if one or both of the parents are homozygous), and by gradually building up the number of genetically resistant animals within a herd and continuing to select bucks who definitely carry this genetic trait as the service sires for subsequent offspring, the increasing incidence of heterozygous and homozygous parents producing kids should certainly accelerate the transmission of this scrapie resistant trait throughout the herd. This in turn is probably one of the best strategies we have available now to minimize the overall herd risk for this deadly scrapie disease.

Figure 1: Inheritance resistance (read the entire WUR presentation here)