 especially pink eye flies are a main way to spread it from animal to animal and also the bacteria can be picked up on the fly to spread to the neighbor but also it's just a source of irritation for their eyes and once you get them irritated they're much more likely to get infected so you can do things like insecticide fly tags so they always have that insecticide right next to their eye I kind of like that you can also do some pour-ons occasionally