Scrapie transmission in Britain: a recipe for a mathematical model

Responses to an anonymous postal survey concerning scrapie are analysed. Ri sk factors associated with farms that have had scrapie are identified as si ze, geographical region, lambing practices and holding of certain breeds. F urther analysis of farms that have scrapie only in bought-in animals reveal s that such farms tend to breed a smaller proportion of their replacement a nimals than farms without scrapie. Farms that have had scrapie in home-bred animals have attributes associated with breeding many animals: large numbe rs of rams bought, few ewes bought, and many animals that are home-bred. Th e demography of British sheep farms as described by size, breeds, purchasin g behaviour, age structure and proportion of animals that are home-bred is summarized. British farms with scrapie reveal certain special features: the y have more sheep that are found dead, more elderly ewes and more cases of scab.