Scrotal circumference is an indicator of a bull's fertility. A larger circumference is preferred and is an indicator for his sons to have a larger scrotal circumference and his daughters to reach puberty sooner and therefore have calves sooner.
Gestation length is an indicator of the probability of dystocia. The longer a calf is in utero the larger it will be at birth and the greater the chance of it having dystocia. It also gives the cow a larger postpartum interval between pregnancies. A shorter gestation length is usually preferred because of this.
Stayability is an indicator EPD of longevity of a bull's daughter in a cow herd. The higher the EPD value the greater chance a cow will stay in a herd over six years and continue producing quality offspring.