Scrotal shape and size can be an indication of a bull’s fertility. You can usually tell by visual inspection whether a mature bull has adequate scrotal size. Measurements are helpful, however, when evaluating very young bulls to see if they are up to standard for their age group.

The shape of the scrotum is important. A bull must be able to easily raise and lower his testicles for proper temperature control. Testicles should hang down well away from the body in warm weather. There should be an obvious “neck” at the top of the scrotum, with the testicles hanging down large and pear-shaped.

A bull with a straight-sided scrotum or a V-shaped scrotum (tapering to a pointed tip) is often not as fertile as a bull with a normal scrotum, according to Veterinarian John Kastelic of the University of Calgary, who has done a great deal of research on bull fertility.

Beware of selecting a bull with odd-shaped testicles, such as one obviously smaller than the other, he advises. Scabby, thickened skin — especially on the back and bottom one-third of the scrotum — may indicate frostbite. Depending on the extent of damage and scarring, this can cause temporary or permanent infertility.

“Bulls with low fertility tend to have offspring with low fertility, and their daughters pass on low fertility to their sons.” — John Kastelic

If there’s any doubt as to whether scrotal size is adequate, scrotal circumference is easily measured. Most breeders offer this information on bulls they sell. There is a correlation between scrotal circumference in a bull and the fertility (as measured by onset of puberty) in his daughters.

To measure a bull, confine him in a chute, take hold of the neck of the scrotum to gently force the testes down into the scrotum, and put the measuring tape snugly around the largest circumference. A breeding soundness evaluation (sometimes referred to as a BSE) should always be conducted, however, to confirm fertility, regardless of the measurement.

For best fertility and to ensure high fertility in a bull’s offspring, select bulls above average in scrotal circumference. The beef industry for many years, has selected bulls primarily for performance traits — rate of gain, feed conversion, muscling, carcass yield, etc. — rather than reproductive traits. Research has demonstrated that selection for increased growth rate in bulls may result in later maturity. Later-maturing, large-framed bulls tend to have smaller scrotal circumference, says Kastelic.

“Small testicles have also been associated with bulls that have exceptionally good muscling and high carcass cutability. When selecting high-performance (fast-growing) bulls, make sure they are reproductively sound. A high rate of gain and/or superior muscling is not much value if the bull has poor breeding performance and can’t settle an adequate number of cows or sires heifers that are not very fertile as cows,” he says.

Bulls with small testes have lower sperm production and often suffer other problems that make them subfertile or infertile.