Case-control study of orf in preweaned lambs and an assessment of the financial impact of the disease

Abstract

Orf, a viral disease which causes proliferative skin lesions around the mouths of lambs and on the teats of ewes, has long been assumed to have production-limiting consequences. This case-control study involved the collection of data from naturally occurring outbreaks of orf in young lambs on eight commercial farms in north-east England. Measurements of weight were taken and orf lesions were scored on a numerical scale for 44 orf-affected lambs, matched to unaffected controls within the same group. Data from corresponding ewes were available from five farms. Paired t tests showed that affected lambs weighed approximately 10 per cent less than their unaffected controls for a period of at least five weeks following the start of the outbreak. The effects were highly significant whether the orf lesions affected the mouth or were found elsewhere on the body. If a lamb had orf, then there was a 82 per cent chance that its mother also had orf on its udder or teats. The financial consequences of orf in young lambs were estimated using average UK figures and conservative assumptions based on the results of this study.