The reason for the outbreak of mad cow disease is that some feed processing plants in Britain and many European and American countries process the viscera and bones of sheep and other animals into animal feed. It is estimated that some cattle feed comes from the internal organs of sheep suffering from scrapie. There are many scrapie in Britain, which is a naturally contagious neurodegenerative disease of sheep and goats. The incubation period is long and it is not easy to detect at first. The onset of animal diseases begins with the itching action of scraping fences frequently, so it is named sheep itch disease. Sick sheep gradually develop tremor and dyskinesia, and most of them die within 6 weeks to 6 months after onset. The pathogenic factors of scrapie in sheep have been transmitted to many laboratory animals, such as mice and hamsters.

Cattle will suffer from mad cow disease after eating feed containing the causes of itching in sheep, and other animals will suffer from similar diseases after eating these feeds. Therefore, scientists believe that mad cow disease is probably obtained by eating feed with sheep pruritus.

Sheep pruritus has a history of 260 years in Europe, and feed processing plants have a long history in Europe. Why hasn't mad cow disease happened before? The reason may be related to the production procedures of feed processing plants. Around 198 1 year, due to economic reasons, the British animal feed processing industry changed its processing mode and cancelled two key steps that could destroy pathogenic factors: one was to cancel the use of organic solvents; The second is to cancel long-term high-temperature steam disinfection. Therefore, there are enough pathogenic factors in animal feed, and animals will get sick after eating these feeds for several years. The British government has taken a series of measures to control the spread of mad cow disease, including stopping feeding feed that may contain pathogenic factors in July, 1988, and slaughtering sick mad cow disease cattle, which effectively controlled the spread of mad cow disease. Scientists estimate that mad cow disease will gradually disappear in the near future.