As cloven-hoofed animals, pigs and sheep are susceptible animals to foot-and-mouth disease. Doing so will obviously increase the probability of infection and increase the difficulty of epidemic prevention. To put it bluntly, pigs may be infected with a foot-and-mouth disease. Pigs themselves will not get sick, but sheep will get sick. As a result, you often have no good effect on the prevention of sheep and have not solved the problem from the root. The reverse is also true.
Foot-and-mouth disease is just one of them, and so are many other diseases. One kind of animal is not sensitive, but it can be preserved, which can cause persistent diseases of another sensitive animal for a long time, so it is best not to polyculture.
Not only pigs and sheep, but also other animals should not be mixed together. Polyculture will complicate animal diseases. Treatment and prevention alone cannot fundamentally solve the problem, so animal husbandry generally pays attention to raising different animals in different areas.
There is a saying in animal husbandry that "pigs don't raise sheep". Have you ever heard of it?