To add clarification to Dan's answer, the detached structure would require flood insurance if the vet chiropractic business operates out of the stable. If the vet business doesn't (such as operating out of a third building), and the stable is solely used for personal/household purposes, it could qualify for the detached structure exemption (assuming it also does not serve as a residence.
It can be a bit complex to dot all the i's and cross all the t's on the detached structure exemption. Rather than expand on this thread about all of the requirements, here is an article on the detached structure exemption that lays out the requirements:
https://www.compliancecohort.com/blog/detached-structure-flood-insurance-exemption