Field evaluation of OJD control using Gudair.

Abstract

A 5-year field trial was undertaken to determine the efficacy of a killed M. a. paratuberculosis vaccine, GudairTM, for the control of OJD in Australian merinos. The vaccine stimulated cellmediated and humoral immune responses. Gudair™ reduced mortalities due to OJD by 90% and delayed faecal shedding for the first year post-vaccination (pv). Thereafter, the prevalence of shedders among vaccinates was reduced by 90%. The numbers of M. a. paratuberculosis excreted by the vaccinated groups were also reduced by at least 90% at most sampling times. However, high levels of excretion by vaccinates occurred on some occasions, and although only 7 of 600 vaccinates died from OJD, all had multibacillary disease. Thus there remains a risk that some vaccinated sheep could transfer the disease. Small reductions in liveweight gain were found in vaccinated lambs in the first year pv, but there was little effect on condition score or wool production. Vaccine injection site lesions were detected in almost 50% of sheep 2 months pv, and these persisted for at least 4 years in 20-25% of vaccinates. Data from this trial enabled the registration of Gudair™ in Australia in 2002 and underpins the pivotal role of vaccination in the current management of OJD.