5 11.7 Concentrates were likely to contain some level of MBM, though the extentto which it was included cannot be ascertained with precision. However, inclusion rates were lower for sheep feed than cattle feed, and the per capita exposure to MBM would have been significantly lower for sheep than for cattle. The feeding of MBM to sheep was prohibited by the ruminant feed ban that came into forcein June 1988. Scrapie is a transmissible spongiform encephalopathy mainly affecting sheep, though goats are also susceptible. It was first recorded in Britain around 1732, and by the time BSE emerged it was widely recognised by farmers and vets.
Transmission occurs naturally between sheep, though precise routes are unknown.
One route may be infected placentae. It is believed to spread between sheep in pastures and particularly in spaces where sheep are congregated, such as lambing pensand paddocks. 11.10 Farmers try to rid their flocks of scrapie by ensuring that scrapie-suspected animals are removed at the earliest opportunity. Selective breeding has also been used in an attempt to prevent scrapie from entering the flock by vertical transmission. For example, since scrapie was made a notifiable disease on 1 January 1993, the Meat and Livestock Commission has recommended that farmers implement a closed flock policy, with purchases only from scrapie-free flocksof preferably older ewes less likely to develop the disease.