Each gram of testicle produces 15 million sperm per day. Total sperm production for both testicles should be at least 6 billion a day. Research has shown that testicular size in bulls is an inherited trait. A producer who chooses bulls will a larger SC is selecting for reproduction over other production traits such as growth rate or frame size. Bulls with a lower SC may produce normal sperm and might perform adequately with a small group of cows, but they cannot meet the demands of moderate to heavy breeding pressure.
Scrotal circumference varies with the breed and age of a bull.
The most significant testicular growth in a bull occurs from the ages of 6 to 36 months. Selection of potential herd sires is often done at 12 to 14 months and is based on scrotal circumference. Various breed associations and bull sale organizations have developed guidelines for the minimum SC of bulls at different ages. Examples they have given are presented in the following table. With advancing age, testicular tissue may lose some sperm producing capacity.