A very interesting read
A TLDR version:
It looks like Mycoplasma Bovis is transmissible through (frozen) bull semen, even though that's been treated with antibiotics.
It looks like that could explain how the particular genotype of M. Bovis found in NZ matches that from Europe - rather than more likely sources if it had been transmitted here by other routes.
Imported semen is still being used - now.