Bos indicus bulls - watch that sheath


Bull infertility is a major cause of production loss in many beef breeding herds. It can result from:

  • poor quality semen
  • lack of libido (sex drive)
  • physical abnormalities preventing service, including overgrown and turning feet; arthritis; uneven, small and/or soft testes; and poor sheath/penis structure
  • reproductive disease
  • general illness
  • injury

In Bos indicus bulls, the most common physical abnormality causing infertility is poor sheath/penis structure. This Agfact describes both desirable and undesirable sheath structure. It is a guide to assist selection of Bos indicusbulls for high fertility.

Three stages of normal service
Normal service involves the following three stages (see Figure 1):

  1. Penis and prepuce at rest.
  2. Penis at mid-erection (prepuce unfolds along the penis).
  3. Penis erect. After positioning of the penis, it is inserted and ejaculation occurs. Penis and prepuce immediately return to rest.
  4. The three stages of normal service

The ideal sheath (see Figure 2) is one that:

  • is light
  • is loose
  • is firmly and evenly attached to the underline for its whole length to achieve the desired angle
  • does not have large areas of loose skin at the navel or around the sheath
  • has no sign of protruding prepuce

An ideal sheath on a 2-year-old bull

A moderate, acceptable sheath on a 3½-year-old bull.

Structural faults can predispose breeding organs to injury and cause loss of bull use.

Common structural faults of sheath/penis found in Bos indicus bulls are:

  • sheath too pendulous and loosely attached
  • sheath/penis too heavy and large
  • protruding prepuce
  • poor attachment to the body in the navel region

Faults such as these predispose bulls to injury, infection, prolapse of the prepuce and subsequent loss of use during their working life. These problems also worsen with age so that if they are apparent in young bulls, they will probably become more so as the bulls age.

Sheath too pendulous and loosely attached

Figure 3. A most undesirable, poorly attached, pendulous sheath on a 12-month-old bull. A penis hanging this close to the ground increases the risk of injury.

The closer the sheath hangs to the ground, whether well angled or not, the more likely it is that the sheath will be irritated or injured. It may even be stepped on by the bull himself when rising after lying down.

Bulls with too much loose skin in the sheath and navel area can have trouble in accurately controlling the sheath during service.

Avoid selecting a bull with a heavy navel fold as it can interfere with erection and injure the penis at service. The curve of the sheath should closely follow the underline and be evenly suspended but firmly attached for all its length.

A pendulous sheath in conjunction with a big, heavy penis is very undesirable.

Sheath/penis too heavy and large

Figure 4. The faults with this sheath are that it is too heavy and thick as well as being pendulous and at a bad angle.

The disadvantage of a large, heavy sheath/penis is that it is subject to injury at service by being harder to control and less flexible. A thick penis or prepuce is also often related to excessive membrane within the sheath—a bad trait as it is associated with prolapse.

These structural faults are more common in Bos indicus derived breeds than pure Bos indicus breeds such as the Brahman, Sahiwal and Red Sindhi.

Usually, the pure Bos indicus bull will have a loose and often pendulous sheath with a light, small penis. A light penis in a loose, pendulous sheath is preferable to a penis that is heavy and coarse—it is more maneuverable and less likely to be injured.

Some bulls have 5 to 10 cm of prepuce protruding below the end of the sheath. Providing the prepuce is moist, fresh and pink, this is not a problem because it means that the prepuce can be retracted. It is, however, a warning sign that the bull may prolapse in future. Although such bulls often have a normal working life, the risk is there.

Polled bulls are more likely to have this problem than are horned bulls.

Where the protruding prepuce is continually exposed, it means that it cannot be retracted into the sheath. This predisposes such prepuces to become dry, swollen, dirty and infected due mainly to a poor or absent blood supply. This is a serious problem as it indisposes the bull for mating.

Fresh pink prepuceDry, permanent eversion of the prepuce

A sheath will often break away from its bodyline near the navel and hang straight down for 5 to 10 cm. Avoid bulls with this condition as it predisposes the lining of the sheath to a prolapse.

Also, although they may serve normally for a couple of years, the risk of injury is always present.

When selecting Bos indicus bulls, aim for those that have both loose skin and a desirable sheath.

Avoid bulls with a pendulous sheath, too much skin and a heavy, coarse penis as they are the source of mating problems and economic loss.

Selection is always a compromise. While minor deficiencies in sheath/penis structure can be tolerated if the bull has other desirable traits, remember that at all times the risk of penis or sheath injury at service directly relates to the number and severity of faults.


This Agfact was originally written by Phil Doyle, former Livestock Officer (Beef Cattle), with the assistance of Peter Chenoweth, then Deputy Dean, Faculty of Veterinary Science (Clinical), University of Queensland, St Lucia.