Pasture Pickings: LLS vet Bruce Watt shares insight into managing Ovine Johne's disease

LLS Central Tablelands senior district vet Bruce Watt has been called out on several occasions recently to examine a handful of sheep that were weak and emaciated while the remainder of the flock were in top condition.
LLS Central Tablelands senior district vet Bruce Watt has been called out on several occasions recently to examine a handful of sheep that were weak and emaciated while the remainder of the flock were in top condition.

On several occasions over the last couple of months I have been called to examine a handful of sheep that were weak and emaciated while the remainder of the flock were in top condition.

In most cases the owners wanted to know if it was Ovine Johne's disease. After euthanising two or three, I conducted necropsies.

One ewe had well developed cheesy gland abscesses in the lungs, explaining her emaciation.

In the other cases, the sheep had thickened, corrugated intestinal walls, enlarged gut lymph nodes and I could see fine lymph vessels over the surface of the intestines.

These findings caused me to be highly suspicious of OJD, but I sent samples to the laboratory to confirm. Pathologists examined the samples of the gut and diagnosed OJD.

As OJD has been deregulated for some time now, it is not the dreaded diagnosis that it was 20 years ago.

The question of what to do now is a commercial disease control decision (although OJD remains a notifiable disease with different implications in areas with a low prevalence).

Should the owner commence a vaccination program and if so, how should it be started, and which age groups?

We know from years of high-quality research, that the vaccine is highly effective in preventing deaths from OJD and reduces, but does not eliminate shedding.

Submandibular oedema in a wether suspected of having OJD. Photo: Bruce Watt

Submandibular oedema in a wether suspected of having OJD. Photo: Bruce Watt

So, if the losses are escalating now, commencing a vaccination program with the current lamb crop is usually the first step.

However, is there any point in vaccinating say two or three-year-old ewes if they may already have been exposed to the OJD bacteria? The benefits here are uncertain.

With current sheep values, I suggest for self-replacing Merinos in our area, it is almost certainly worth vaccinating the hoggets and almost certainly not worth vaccinating the five-year-olds.

Whether it is worth vaccinating the two, three and four-year-old depends on your enterprise (Merinos are more susceptible than British breeds), likely level of exposure, budget, attitude to risk and your ability to safely vaccinate mature sheep.

Wethers are also susceptible to OJD so wether lambs should also be vaccinated unless they are to be sold as lambs or young hoggets.

Finally, when discussing OJD vaccination, I caution owners that the vaccine is dangerous if accidentally injected into people and needs to be administered correctly.

If in doubt, discuss this with your animal health adviser. As the OJD vaccine 'Gudair' is distributed by Zoetis, their technical experts are a great resource too.