Scrotal circumference, expressed in centimeters, is our best tool to estimate a bull's sperm production and is one component of a breeding soundness exam. Breed average at 365 days is 36 cm. Minimum acceptable size at 365 days is 30 cm, but 32 cm may be a more comfortable minimum. There is no evidence that above average scrotal bulls are better breeders. Using bulls with higher scrotal circumference EPD's will help increase the scrotal circumference among your bull calves.
  Breeders producing calves with acceptable testicle size can feel comfortable using bulls with scrotal EPDs into the negative range on cows that are close to 0 EPD. As an example: assume a breeder has an average cow herd (+.0 scrotal EPD) and is producing yearly bulls with average (36 cm.) scrotal size. If he uses a bull that is strongly negative (-1.00 scrotal EPD) on his cow herd, the bull contributes 50% to the progeny, given normal nutrition, environment, and genetic distribution, he can expect the resulting yearling bulls to have an average scrotal measurement of 35.5 cm, still well into the acceptable range.
  The problems arise when you stack strongly negative scrotal sires on top of cows with negative scrotal EPDs. Given the standard deviation in scrotal size of + or - 3 cm, breeders may begin to experience a small percentage of young bulls falling below acceptable scrotal circumference as they compound negative scrotal EPDs in their pedigrees. Breeders experiencing problems with small scrotal size in their bulls or whose cows have very negative scrotal EPD's should avoid using bulls with strong negative scrotal EPDs.
  While there is some correlation between testicle size in a bull and the age at puberty of his daughters, the effect is so small as to have little practical application. There is no evidence that scrotal circumference can be used to predict female fertility. Monitor scrotal size of your bull calves and strive to stay within the acceptable range. As always check the accuracy level of all EPDs in your evaluations. Discriminating against good bulls with negative scrotal EPDs without very good reason will unnecessarily limit your sire selection.