B. Definitions (pdf)


Maedi Visna (MV), also called ovine progressive pneumonia (OPP) is a viral disease of sheep and is caused by infection with maedi visna virus (MVV)

  • Clinical signs which occur primarily in adult sheep include: unexplained weight loss (chronic wasting); decreased exercise tolerance; respiratory distress; and hard udder at lambing. 
  • Production losses in infected sheep are: decreased reproductive performance; higher lamb mortality rates through mismothering; early culling; and lower weight gains by lambs because of poor milk production.
  • Once a sheep is infected with the virus, it remains infected for its lifetime. 
  • The virus is shed through respiratory secretions, colostrum and milk. Infected sheep produce antibodies to the virus which are detected by serological tests. 
  • It takes 2 weeks to 8 months to produce detectable antibodies after infection.


Must means that the owner of the flock, or their designated agent is required (obliged) to carry out the stated activity as described, i.e. it is not voluntary.


A sheep is a ram, ewe or wether (castrated male). 
Usually, a sheep is ≥ 365 days of age, but for parts of this program, this term may be used for sheep ≥ 180 days of age.


All goats residing in the flock are required to be subjected to the same testing and removal protocols as sheep. 
This is because goats can become infected with MVV and may be able to transmit the virus to sheep.   Therefore when the protocol says “sheep”, it also applies to any goats in the flock or housed anywhere on the flock premises.  All testing and biosecurity protocols apply equally to goats and sheep.


A lamb is a ram, ewe or wether < 180 days of age and is the offspring of both the birth dam (natural mother or embryo recipient) and of the foster dam (if the lamb was cross-fostered). 
When determining disease status, the following is considered:


Serological status of birth mother (natural or – if transferred as an embryo - recipient).

Serological status refers to the presence of antibodies produced by the immune system in response to infection by the virus, and detected by a serological (e.g. blood) test.  The test does not detect presence of the virus – only the antibodies.


Serological status of foster dam if cross-fostered at any point while nursing.


Not the serological status of the sire.


The serological status of the genetic dam (donor) in cases of embryo collection and transfer,


Unless if the embryos have been handled in accordance with the protocol set out by the International Embryo Transfer Society for the sanitary handling of embryos http://www.iets.org/index.asp


A flock for purposes of this program, is a population of sheep and goats which at any time during the year are managed together, i.e. if sheep share pastures, housing, feeders, watering or other equipment that has not been disinfected between groups, then they are considered part of the same flock even if they reside at different farms for part or all of the year.


A flock premise is comprised of all buildings, dry lots, paddocks/corrals, and pastures occupied at any time of the year, by the flock.


To remove from the flock suggests that the MVV test positive sheep or lambs from MVV test positive ewes, are to be sold directly to slaughter for meat and not as breeding stock. 
This is a strong recommendation and the actual disposal fate of the animals is not enforced by this program.


The test date is the date that the blood samples were taken from the sheep, not the date that the results were received.