I dont see the point at all of crossing bulls into terriers for working ability,maybe if a line had got to close and was producing weak spindly terriers with poor heads and jaw maybe,but i would never put bull blood into to improve working ability,theres nothing they can do that a pure bred working terrier to working terrier cant do,ive also found them over hard and try to fight quarry instead of working it,i have seen and worked bull blooded terriers and dint bother with them very long they were slow starters and permanently in sick bay which is not what i want i guess there is some good ones