A Preliminary study on the potential cost at slaughter of OJD vaccination site lesions to the Australian sheep industry National Ovine Johne’s Disease Control and evaluation Program

Summary

This report assesses the risk of discounts being applied to slaughtered sheep carcases as a result of the presence of OJD vaccination site lesions as the use of vaccine expands to control the on-farm impacts of OJD in Australia. It reviews the literature on discounts as applied in New Zealand and examines the actual discounts applied to 20 sale lots of vaccinates slaughtered in Australia.

At the time the project was commissioned by MLA, vaccine use in Australia was limited but expanding. Anecdotal reports from New Zealand had suggested that discounting of vaccinates because of the existence of lesions was very real. It was therefore timely to assess the risk of a significant reduction in the value of Australian sheep meat if vaccination against OJD was to become widespread.

As expected there was little reliable objective survey data on the prevalence or degree of discounting in New Zealand due to vaccination site lesions. What is available suggests that the greatest discount is applied to trimmed high value lamb carcases that are destined for export in whole carcase form as a result of downgrading to a lower quality grade. However this is likely to overestimate the current discount in New Zealand as the proportion of both lamb and mutton exported as carcases has fallen significantly since this report was written. Despite this, anecdotal reports suggest that the perception of the risk of discounting is sufficient to limit the use of vaccine by the New Zealand industry.

In Australia a number of factors will act to minimise the degree of discounting applied to vaccinated carcases. These include; our ability to avoid vaccinating slaughter lambs due the greater use of crossbreeding in our lamb industry; the relatively small expected prevalence of lesions in vaccinated mutton carcases as a result of the long interval between vaccination and slaughter; and the low proportion of our sheep meat that is exported in whole carcases form. However the recent trend for pure Merino lambs to be slaughtered as prime lamb could mean that an increasing proportion of high value lamb will contain lesions that will require trimming. This trend should be monitored.

The results of the pilot survey support the conclusions of the review. The prevalence of lesions was high (65%) in lambs slaughtered within 6 months of vaccination but was low (18%) in mutton sheep vaccinated 12 months or more before slaughter. Despite this there was an insignificant value of carcase removed as trim, there was no additional labour cost associated with the trimming, nor was there any downgrading of trimmed carcases to lower value grades.

The results of this work will be of benefit to producers, processors and policy makers. It predicts that OJD vaccination site lesions will not be a significant cost to producers or the processing industry and will represent only a very small proportion of the total cost of OJD control by vaccination. However because of its preliminary nature this project examined only a small number of vaccinated sale lots in a market experiencing a severe undersupply of slaughter sheep. It is recommended that the processing industry’s response to lesions be monitored at a time of better market supply. Further all sale lots were vaccinated at the recommended site high on the neck behind the ear and the costs may be greater if producers vaccinate at alternate sites. It is recommended that the importance of, and reason for, using the recommended site of vaccination be highlighted to producers.