I would argue that it would include especially breeds that are considered rare/endangered, if we ever go down that route in PZ! The livestock community at large has so many people dedicated to conserving rare breeds, and even most commercial farmers in my experience will keep at least a small stock of something more unique that they have a personal interest in. Given that zoo management is generally focused on good conservation management, zoo collections can also host a fair number of rare breeds and have a much greater reach in regard to educating people about them.
Most zoos I've been to seem to have some sort of rare breed pig. I don't know why it's usually pigs, but it's something I've noticed enough to take note of. Interestingly a keeper I knew once mentioned to me that whenever they asked guests what their favourite animals at their zoo had been, the pigs they had consistently rated in the top 5.
