Because they are naturally good at hunting rats, you may want to stop them doing this, to prevent scratches and bites. (petpeoplesplace.com)
Under other exemptions, hunting a rat with a dog is fine, but to do the same to catch a mouse is illegal. (politics.co.uk)
It was used for hunting rats in an unusual way: first ferrets were sent into rat burrows and when the rats scurried out, the Airedale's would then take up the chase. (wileypup.com)