Sometimes none of the above -

https://www.mpi.govt.nz/news/media-releases/mpi-introduces-new-biosecurity-sniffers/
>The detector dogs on show at the Auckland Biosecurity Centre today included media celebrity Clara, a recently graduated border biosecurity dog, and Boston, a springer spaniel that MPI is training to work in the field to detect any pest that makes it across the border.

>“We are working to develop a new type of dog that will be able to help with biosecurity responses. It will have the flexibility to be trained to detect any new pest that makes it to New Zealand.”

>Steve Gilbert, MPI Director Border Clearance Services says traditional border biosecurity dogs are not suitable to act in the incursion role, as they are trained to sniff out food and could be distracted by food odours when working outside.