Diseases like ASF, or African swine fever, are very highly transmissible. I'll throw avian influenza in there, as well. AIA is devastating to poultry flocks, and quite often, the quarantine area is not just the farm that it occurs on, but a larger area where birds have to be destroyed.
You can talk about infectious diseases coming into cattle operations, and even go so far as to say that bringing in invasive species into crops could impact a farm's livestock operation as well. It's devastating to not only the producer where it happens but also the entire area in which it happens is quite often affected. It affects multiple producers, costing hundreds of thousands or millions of dollars.
Potentially, depending on the livestock, it could create shortages in that product as well. It really does have a devastating effect, which is why we need to strengthen our trespassing laws.