C. Protocols

Protocols for selecting sheep for sampling (pdf)
15. Random Sample Flock Test - how to select sheep for sampling:


For “A” status or Monitored or Monitored-Low Risk flock test.


Only sheep ≥ 365 days of age are eligible for testing.


The number of sheep to be tested is determined by the table in Appendix 9.



This number is determined to detect MV infection at a prevalence of ≥ 5% of the flock with 95% confidence that this level of flock infection is detected. The example given in the appendix is for use when the test has a sensitivity of 99% and specificity of 100%.




I.e. if at least 5 of every 100 sheep in the flock are POSITIVE, then there is a 95% chance that at least one infected animal will be found on the random test.



It will not reliably detect a prevalence of MV infection < 5% and will not reliably detect infection if the test used is less sensitive.



The animals selected for testing must be randomly selected to ensure an accurate flock test.


Recommendations on how to randomly select sheep for testing are outlined in Appendix 9.

16. Avoid Sampling the Flock Around the Time of Lambing.
  There is evidence that infected pregnant ewes may not test POSITIVE within one month of lambing (before and after).  This may be because the ewe moves large volumes of immunoglobulins (antibodies) into her colostrum, or because its immune system is stressed from pregnancy or lactation.  For this reason, it is strongly recommended that flock tests be scheduled so as to avoid sampling within 4 weeks of the expected lambing date until at least 4 weeks post-lambing.
17. Avoid Sampling Soon After Vaccination.
  There is evidence that a strong stimulation of the immune system, e.g. from vaccination – may increase the chance of sheep testing NON-SPECIFIC.  This is because the immune system is activated.  A NON-SPECIFIC test result has nothing to do with MV infection status but interferes with the testing procedure.  For this reason, it is strongly recommended that flock tests not be scheduled for up to 3 weeks after vaccination but may be done on the same day as vaccination.