July 15, 2003
The National Scrapie Eradication Program: Questions & Answers
The following scrapie question-and-answer piece is the second such column to appear in the Sheep Industry News. It is being brought to you by the U.S. Department of Agriculture?s Animal & Plant Health Inspection Service, which oversees the National Scrapie Eradication Program. If you have a program-related question you?d like answered, please e-mail it to Sheep Industry News Editor Laura Gerhard at email@example.com, fax it to Gerhard?s attention at (303) 771-8200, or write: ASI; Attn: Laura Gerhard; 6911 S. Yosemite St.; Centennial, CO 80112-1414.
1. I have a closed ewe flock but I buy outside rams to introduce new genetics into my flock.
Does this activity increase my risk of introducing scrapie into my flock?
Rams have not been shown to transmit scrapie infection, so the risk of them infecting your flock is very small. However, rams will significantly affect the genetics of your flock and as a result can make your flock more or less susceptible to scrapie if you choose to bring in ewes in the future.
What can I do to raise the resistance of my band of ewes to scrapie in case they were ever exposed to scrapie?
The rams can alter the collective susceptibility or resistance to scrapie within the replacement ewe lambs retained in the flock. Rams that are QQ at codon 171 will over time increase the frequency of Q at codon 171 and increase the overall flock susceptibility to scrapie. Conversely rams that are RR at codon 171 will only produce lambs that have increased resistance to scrapie. QR rams have an intermediate effect, producing some susceptible and some resistant lambs.
The genotype of a terminal sire is not important unless the flock has scrapie since all of the lambs will be sold for slaughter. In flocks where infection is suspected, even terminal sires should be RR to minimize the number of infected placentas produced and thereby the amount of premises contamination.
2. How will the Regulatory Scrapie Slaughter Surveillance Program help eradicate scrapie?
Regulatory Scrapie Slaughter Surveillance (RSSS) will allow for more rapid identification of infected and exposed flocks minimizing the spread of scrapie by accelerating the testing and clean up of affected flocks. RSSS targets culled adult sheep. These sheep are required to have official ID prior to being marketed. Cull sheep as a group have a higher risk of containing sheep that will test positive for scrapie because of their age and the likelihood that they were culled for poor performance. Once a positive sheep is found through RSSS, it will be tracked back to the flock of origin and, if possible, birth. Further investigation will be done to determine the scrapie status of the flock(s). If a flock is determined to be an infected and/or a source flock, animals that originated from that flock will be traced to the flocks in which they currently reside. If available, these animals will be tested. If they are not available, part or all of the exposed flock will be tested.