8. CREATING A NEGATIVE FLOCK FROM POSITIVE FLOCK GENETICS PDF version
In some purebred flocks with valuable genetics and a high prevalence of MV positive sheep, it may be desirable to establish a negative flock from lambs born to "positive" ewes. The following outline two methods as to how this might be done and it does not modify the main program.
   
a.)
 Artificial Rearing of Lambs Born to Test "Positive" or Unknown Status Ewes
 
i.
Lambs should be removed at birth and not allowed to suckle from the birth dam because of the risk of MV-v transfer from the milk or colostrum.
 
ii.
 Ovine colostrum from MV negative flocks or bovine colostrum obtained from Bovine Leucosis virus (BLV) free herds should be used as the colostrum substitute. Ideally the colostrum will be pooled to reduce the risk of bovine colostrum anaemia, and should be from older cows vaccinated against clostridial diseases.
  iii. Lamb milk replacer is a suitable supplement to raise the lambs artificially until weaned.
  iv. Artificially reared lambs must be housed separately from the main "positive" flock and from any "negative" enrolled flock and managed in an isolation facility and according to the guidelines in Appendix 9.
  (1) This is because the status of the artificially reared lamb flock is currently unknown.
  (2) Infection with MV-v may also occur from in utero transmission before the lamb is born as well as accidental colostrum intake.
(3) So until proven otherwise, the artificially reared lamb flock is considered high risk.
v. As artificially reared lambs reach 180 days of age, they must be managed separately from any new lambs entering from the positive flock as well as the "positive" and "negative" flocks.
  (1) These isolation facilities must meet the protocols as set out in Section 3.
  (2) When the lambs are 180 days of age, the group of lambs must undergo two negative tests between 8 to 12 weeks apart before entering the flock.
     
b.) Establishing a New Flock From First Time Lambing Ewes. (Appendix 10)
i. This program is suitable for producers that wish to preserve flock genetics, have lots of barns and space but not labour. It requires that for 2 to 3 years, 3 flocks would need to be maintained for a period of time. The protocol is as follows:
ii. First Time Lambing Ewes From Main Flock:
(1) Pregnant ewe-lambs (that have never lambed before) are moved away from the main flock to lamb in a separate premise. They are to be managed as a separate flock following the guidelines available in Appendix 9.
(2) The lambs born to the ewe-lambs are raised until weaning. At weaning (~ 2 months of age), the lambs selected as replacements are moved to a different facility away from the main flock.
(3) Lambs not identified as replacements are marketed for meat.
(4) This first-time lambing flock only needs to exist for ~ 3 months.
(5) The dams are returned to the main flock when their lambs are weaned.
(6) The rationale for using ewe-lambs that have never lambed before:
(a) Young ewe-lambs are likely less infected with MV-v than their older flock-mates.
(b) Young ewe-lambs likely have less damage caused by MV-v if they are infected and may be less likely to pass the infection to their offspring.
iii. Offspring of First-Time Lambing Ewes:
(1) These lambs have a low risk of being infected with MV-v but the risk is not zero.
(2) This flock is subjected to the same testing protocols as for the Whole Flock program (Section 4-a), i.e. should undergo testing as a separate flock when they reach 180 days of age.
iv. Subsequent Additions to Offspring Flock:
(1) The procedure as outlined in Section 8-c-ii can be repeated as necessary but the offspring cannot enter the "Offspring Flock" until they reach 180 days of age and have had 2 negative tests 8 to 12 weeks apart.
v. Main Flock:
(1) This flock can continue to produce market lambs but should be culled as quickly as the producer can afford as it represents a potential source of infection for the "Offspring Flock".