Ovine Johne’s Disease Definitions
A number of specific terms are used as part of the national approach to the management of ovine Johne’s disease (OJD). This Agriculture Note explains these terms.
Abattoir 150 status
At least 150 sheep over 2 years of age (that are representative of the flock) have been submitted to an abattoir in the past 12 months with at least 150 sheep, in 1 or more lots, being examined and found to be negative for OJD. The sheep must have been on the property fro at least 2 years.
Abattoir 500 status
At least 500 sheep over 2 years of age (that are representative of the flock) have been submitted to an abattoir in the past 24 months, in 1 or more lots, being examined and all found to be negative for OJD. The sheep must have been on the property fro at least 2 years.
Assurance Based Credit (ABC) Scheme
A nationally agreed scheme that measures the risk of OJD being present in a flock or mob of sheep. Credit points are allocated to a flock or mob based on the location (prevalence area) of the flock, testing results, vaccination and certification of low risk mobs.
ABC Score
The total number of credit points allocated to a flock or consignment of sheep under the ABC Scheme. (May also be referred to as the OJD Score).
Approved Vaccinate
A sheep that is either:
- vaccinated with an approved OJD vaccine by 16 weeks of age, or
- vaccinated with an approved OJD vaccine after 16 weeks of age and, in the written opinion of a SheepMAP approved veterinarian, vaccination occurred prior to exposure to OJD infection,
and is identified with an approved NLIS (Sheep) ‘V’ tag. (Refer to the Agriculture Note AG1301- Identification of Sheep and Goats in Victoria).
Approved Vaccinate Flock
A flock comprising entirely of Approved Vaccinates (refer ‘Approved Vaccinate’).
Certified Low-Risk Sheep
Sheep which come from a flock which is ‘Infected’ or suspected to be infected with OJD, and which are certified in writing as low-risk by a SheepMAP approved veterinarian on the basis of:
- a risk assessment, and
- an approved Property Disease Management Program (PDMP) that includes profiling, strategic culling and vaccination.
Infected flock
A flock in which:
- infection by the sheep strain of Mycobacterium paratuberculosis has been identified, and there is evidence of, or likely potential for, transmission of infection within the flock, or
- infection by cattle strains of Mycobacterium paratuberculosis has been identified and there is evidence of spread of infection from sheep to sheep in the flock,
and the flock has not met the requirements for resolution of infection.
Monitored Negative (MN1, MN2, MN3)
Monitored negative flocks are currently participating in the Sheep Market Assurance Program (SheepMAP). The flock has been tested to provide 98% confidence that OJD will be detected if the flock prevalence is 2% or higher. Management practices are also in place to avoid the introduction of disease.
Monitored Negative Vaccinating (MN1-V, MN2-V, MN3-V)
A Monitored Negative Vaccinating flock is the same as a Monitored Negative flock, except sheep are also vaccinated against OJD. MN3-V provides the highest level of assurance there is no OJD in the flock.
Nil Assurance (NA)
A flock that has no official history of OJD, (or any suspicion of infection has been resolved), and no other status has been assigned.
A flock status of NA should not be taken to imply freedom from OJD.
PFC 350 test
A test of 350 representative sheep over 2 years of age (or all sheep over 2 years of age in small flocks) by Pooled Faecal Culture in pools of up to 50 sheep. (Refer Agriculture Note: Diagnostic tests for ovine Johne’s diseases).
Prevalence Area
A nationally defined geographic area that has been allocated credit points (Category A of the ABC score) based on the amount of OJD in the area.
Property Disease Management Program (PDMP)
A program approved by the Chief Veterinary Officer (CVO) for the state, and conducted by the owner in conjunction with an approved veterinarian (or DPI animal health staff), to manage OJD in an infected flock.
Second Generation Approved Vaccinate Flock
A flock comprising entirely of Approved Vaccinates (except terminal ‘T-tag lambs) which were born when the whole flock (except terminal ‘T-tag’ lambs) were ‘Approved Vaccinates’.
Sheep Health Statement
A declaration, signed by the vendor of sheep, that shows the ABC Score applying to those sheep. It may also contain information regarding the footrot, lice and ovine brucellosis status of the flock.
SheepMAP
The Australian Johne’s Disease Market Assurance Program for Sheep. SheepMAP flocks have been tested with negative results and have management in place to assist prevent the introduction of OJD into their flock.
Suspected to be infected
A flock is suspected to be infected with OJD, if the owner has reasonable grounds to believe the flock has been exposed to OJD infection based on:
- trace back or trace forward contact with an infected flock;
- contact with OJD contaminated land or facilities;
- a positive Johne’s disease screening test;
- a neighbouring infected flock;
- the introduction of sheep with an ABC score of 0;
- clinical signs of OJD; or
- advice from the Department of Primary Industries, AND
the flock has not met the requirements for resolution of suspicion.
Terminal (‘T’ tag) lambs
Lambs which are to be slaughtered before they cut their first two permanent teeth, and are identified by an approved NLIS (Sheep) ‘T’ tag.
Tested Low Level Infected Flock
An infected flock which has:
- a history supporting a low level of infection,
- an approved Property Disease Management Program (PDMP) in place, and
- the most recent flock profile demonstrated a detection rate of not more than 1 of 7 pools by Pooled Faecal Culture (PFC) within the previous 2 years.
Sheep mobs that contributed to the positive pool are not eligible for this point.
In summary, when purchasing sheep, producers should ensure they understand flock statuses and the ABC score of the sheep they intend to purchase. Producers planning to buy sheep are strongly advised to seek a Sheep Health Statement (SHS). (Refer to Agriculture Note; Assurance Based Credit (ABC) Scheme and Sheep Health Statements).
Further information
Further information about OJD statuses and books of Sheep Health Statements can be obtained from animal health staff at your local DPI office or on the DPI web site http://www.dpi.vic.gov.au/farming/OJD
Acknowledgements
This Agriculture Note was developed by Dr Alison Lee, Biosecurity Victoria – Animal Standards Branch Sept 2006.
It was most recently reviewed by Dr Alison Lee, Biosecurity Victoria in July 2011.
