Prolonged exposure to OJD-contaminated pastures appears to be a major factor leading to high infection rates within flocks. The primary aim of using grazing management as a strategy to manage OJD is to reduce the exposure of lambs to Mycobacterium paratuberculosis both before and after weaning. Ideally grazing management should be combined with an OJD vaccination program.
It is difficult to avoid exposure of lambs to some level of OJD contamination before weaning if they are born into an infected flock. The main source of contamination will be infected ewes and the pastures they graze. Exposure can be reduced by lambing onto specially prepared ‘low contamination’ pastures and by early weaning to separate lambs from infected ewes. It is also important to immediately cull any ewe showing signs of wasting, as these sheep may shed large numbers of OJD bacteria.
Low-contamination pastures can be prepared for lambing ewes and/or weaners in 6–12 weeks during summer and six months in other seasons by:
- grazing with steers
- rotating with crops
- re-sowing pasture
- grazing with terminal lambs and selling them straight to slaughter
If low-contamination pastures are scarce, then preference should be given to the weaners rather than lambing ewes. Hoggets and ewes are susceptible to infection but sheep exposed as adults are less likely to develop clinical disease than those exposed as young sheep and lambs.
More information is available on the Meat & Livestock Australia fact sheet titled ‘The role of grazing management in the control of ovine Johne’s disease’ (PDF 1849 kb)