Changes in ovine Johne’s disease prevalence following vaccination with Gudair™ for an extended period

Summary

​This project was conducted to evaluate the effectiveness of Gudair™ vaccine in reducing ovine Johne's disease (OJD) prevalence in vaccinating flocks over more than one decade. Six biennial faecal samplings were conducted in 12 enrolled flocks that commenced vaccinating lambs in or prior to 2002; three samplings were done in a previous project (OJD.033) and three in the current project. At each sampling, faecal pools created by collecting one pellet per sheep, from each of four age groups (3, 4, 5 and 6 year-old sheep) were selected from each flock.

Actual number and sizes of pools varied. Samples were cultured using pooled faecal culture and the sheep level OJD prevalence was calculated and compared between years. The proportion of positive pools and the animal level prevalence of shedding significantly reduced over time but faecal shedding persisted and was still present in 3 of the 8 flocks (37.5%) that remained in the study at the last sampling conducted in 2013-14. The findings of this project will enable sheep producers make better informed decisions on managing OJD in their farms, and in evaluating the risks of purchasing and trading vaccinated sheep.