H. CREATING A NEGATIVE MV FLOCK FROM “POSITIVE” FLOCK GENETICS. (pdf)

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, some of which may be born to POSITIVE ewes.  The following outlines two methods as to how this might be done but does not modify or supercede the main program.

   
1.
Artificial Rearing of Low-Risk Lambs Born to Test POSITIVE or Unknown Status Ewes
 
a.
Lambs intended to be retained as replacements should be removed immediately at birth and not allow to suckle from the birth dam because
 
i.
There is a high risk of MVV infection from the milk or colostrum.
 
ii.
There is a high risk of MVV infection from the dam's respiratory secretions.
 
b.
Low risk colostrum should be fed to these lambs (Appendix 11).
 
i.
Sheep colostrum from "B" or "A" status flocks.
 
ii.
Heat treated colostrum from NEGATIVE ewes from within the POSITIVE flock.
 
(1)
Colostrum should be heated to 56 C and held at that temperature for 60 minutes to kill MVV.
 
iii.
Cow colostrum from Bovine Leucosis virus (BLV) free herds. If bovine colostrum is used, the colostrum should be pooled to reduce the risk of bovine colostrum anaemia, and should be from older cows vaccinated against clostridial diseases.
 
(1)
It is strongly recommended to heat-treat cow colostrum, using the protocol in Section H.1.b.ii, if BLV status is unknown
 
iv.
Colostrum replacement products fed according to label requirements as a minimum amount.
 
c.
Lamb milk replacer is suitable to raise the lambs until weaned onto dry feed.
 
d.
Artificially reared low-risk lambs must be housed separately form
   
i.
Lambs which may have accidently nursed prior to being snatched.
   
ii.
Lambs not fed low-risk colostrum.
 
iii.
The POSITIVE flock if those sheep are present on-farm.
   
iv.
Any sheep within the flock that are part of the NEGATIVE flock.
 
v.
Any sheep with a pending status (e.g. retest of SUSPECT sheep, new introductions in an Isolation Facility)
e.
Infection with MVV may also occur from transmission of the virus in the womb before the lamb is born.  For this reason, the artificially reared lamb flock is considered high risk until receiving a NEGATIVE test.
f.
It is strongly recommended to manage these lambs as a group (i.e. no additions unless NEGATIVE status is confirmed) and house in an Isolation Facility. 
   
i.
The Isolation Group must meet the protocols as set out in Section C.
   
ii
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.
     
2. Establishing an MV Low Risk Flock From First Time Lambing Ewes. (Appendix 12)
This program is suitable for producers who wish to preserve flock genetics, have lots of barns and space but not labour.  It requires that for 2 to 3 years, 3 flocks will need to be maintained for a period of time.  The protocol is as follows:
a.
First Time Lambing Ewes From Main POSITIVE Flock:
 
i.
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 13.
 
(1)
This group is considered MV POSITIVE but likely low test prevalence of infection.
 
(2)
The prevalence of infection with MVV is likely lower in young ewes than their older flock-mates.
 
ii.
The lambs born to the ewe-lambs are raised by their dam until weaning.
 
(1)
At weaning (~ 2 months of age), the lambs selected as replacements are moved to a different facility away from the main flock.
 
(2)
Lambs not identified as replacements are marketed.
 
(3)
Their dams are returned to the POSITIVE flock when the lambs are weaned. 
 
b.
Offspring of First-Time Lambing Ewes:
 
i.
These lambs have a low risk of being infected with MVV but the risk is not "zero".
 
ii.
This flock is to be treated as a separate flock (“Offspring Flock”) and subjected to the same testing protocols as for the Whole Flock program (Section D), when they reach 180 days of age
 
c.
Subsequent Additions to Offspring Flock:
 
i.
New lambs reared as outlined in Section H.2.a. may not enter the “Offspring Flock” until they reach 180 days of age and subsequently have had 2 NEGATIVE tests 8 to 12 weeks apart.
 
d.
POSITIVE Flock Disposal
 
i.
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".

 

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