Heredity plays a part in everything. Some hounds are almost impossible to break from off game. Some will leave a hot rabbit during a driving race to go off by themselves on off game. Other hounds are so naturally “straight” to rabbits that they spend their whole lives running nothing but rabbit without ever being corrected. Hounds from lines known to be steady to off game or extremely easy to break tend to reproduce that trait when bred. Not just in beagles, but in other hound breeds as well.
Its in the genetics, I had a 15 inch male L/W that was running a rabbit pretty good at 5-6 months old. At 8 months he was running deer even better. Took him to a deer breaking pen, twice, last time he sniffed the nose of the deer. He was lit up both times at the pen, in the pen for 40 minutes each time he went to the fence and was chewing on the wire to get out, his eyes were blood shot due to the blood vessels breaking when shocked. Gave him to an older man who ran rabbits, he loved him. I could not trust the dog so he was gone. Come to find out on the sires side there was a history of deer running. Never ever thought about breeding to the male ever again. JMO