Mark Purdey animal feed dates back to at least 1926. In the 1970s attention was directed within MAFF to the danger that this practice would result in the spread of infectious diseases. The diseases considered were those caused by conventional viral and bacterial organisms. No consideration appears to have been given to the risk that scrapie might be recycled in sheep, or even transmitted to other farm animals. This may seem surprising. The answer probably lies in the fact that half a century had elapsed without any indication that animal feed containing ovine protein was infecting sheep or any other animal." Purdey
Ovine pulmonary adenocarcinoma of lung fluid produced by the affected lung tissue; lifting the hind legs of the animal above the level of its head will cause large volumes of this fluid to flow from the nostrils. There are no reliable tests for the diagnosis of OPA in live animals which are suitable for use on farms, so diagnosis can only be confirmed at necropsy (post-mortem examination). On necropsy, lungs are interspersed with multifocal tumors. Some of these are small discrete nodules and others will involve the entire half of a lung lobule. JSRV acutely transforms the lung epithelia into cancerous cells, with