Changes to the Maedi-Visna Flock Status Project

 Recent changes to the Maedi-Visna Flock Status Project have increased the program flexibility and decreased the cost of accreditation.  Maedi-Visna is a common infectious disease that decreases lamb growth and ewe reproductive performance.  The Maedi-Visna virus is detectable in the blood of infected sheep using a relatively simple laboratory test.  There is no cure and infected sheep must be culled to prevent further spread of the disease within the flock.  The Maedi-Visna Flock Status Project was started in 2000 as a collaborative initiative involving Ontario sheep producers, the Ontario Sheep Marketing Agency, The Canadian Food Inspection Agency, and the University of Guelph.  Since 2000, over 9000 blood samples from 47 Ontario flocks have been tested through the project.   The infection rate on the first test ranged from zero percent to over 50 percent of the flock.  A major goal of the project was to establish on-farm testing protocols that would be effective in detecting infected animals and preventing the reintroduction of the disease once the flock was ‘Maedi-Visna free’.   In reviewing the histories of the test flocks, it was found that once a flock has tested negative and bio-security guidelines were followed, the risk of additional sheep testing positive was very low.  It was determined that the testing schedule could be changed in the following ways to minimize costs to producers, while still ensuring the effectiveness of program (see diagram below for details):

·        The number of tests required to obtain an ‘A’ status with the project is two whole flock tests and one partial flock test (all sheep sampled must test negative).  Previously, three whole flock tests and one partial test were required.

·        Provided that all animals test negative, the length of time between the first and second full flock tests has been increased from six months to one year.  

·        Producers with closed flocks only need to test every second year after reaching an ‘A’ status.  ‘Closed flock’ is defined as having no new sheep, even those from ‘A’ status flocks, brought on to the farm.  New genetics are introduced through semen and embryos from sheep testing negative for Maedi-Visna or washed embryos.

 To further increase the flexibility of the program, the following changes regarding show (exhibition) sheep have been made to the bio-security requirements:

·        Enrolled and ‘B’ status producers wishing to show sheep are allowed to reintroduce sheep to the flock without testing. However, testing is still highly recommended to avoid jeopardizing the negative status of the flock.

·        For ‘A’ status producers, sheep returning to the home flock must be isolated until they test negative twice, before they are mixed with the rest of the flock.

·        Any sheep leaving and returning to the farm must be included in the next full flock or random test.

 What has stayed the same?

·        The Project is still open to all Ontario sheep producers.

·        Producers still receive a discount on Maedi-Visna testing.

·        Producers still may choose between a Whole Flock test or Monitored test depending on their goals.

·        Until the project completion date of March 2006, the Maedi-Visna Flock Status Project is still your best option for controlling Maedi-Visna in your flock. For more information about the project, contact the Ontario Sheep Marketing Agency (519-836-0043; projects@ontariosheep.org).