My Border terrier is a fanatical ratter but the only bother she gives the chickens
is to try to pretend she is one so she can steal her food
. So altho they might be more likely to be 'chase anything', it doesnt necessarily follow.
I even dangled her upside down and kicked open a flip top feed bin once and dunked her in head first as there was a rat inside, all I heard was a muffled rolling growl, a shake , a single squeak and Mission Impossible was complete! She will happily sit for an entire day watching a hole, try getting her to sit any other time...
Shes not from ratting stock and was never trained, she just adores it. Wish Id got two so it was easier for her to corner the rats, thats the only problem with one (the Doberman tried his best but it's like having Goofy/Scooby Doo on the case...)