I'm attaching a screen shot of emails I exchanged with Lynnette Hart of UC Davis, one of the authors on the UC Davis studies of the risks and benefits of spaying various breeds of dogs. She says that "Generally small breeds are not affected." The June 26 seminar at UC Davis sounds like it will be very interesting. It's available to view live as it happens, but unfortunately I won't have the time to watch it, and registration to view it live costs $150. If anyone on Yorkietalk has the time and the money, registration information can be found here:
2017 International Society for Anthrozoology Conference | Continuing Education