In order to be a successful breeder, a bull must produce adequate amounts of fertile semen and must be able to deliver that semen to the reproductive tracts of cows. There are a number of injuries a bull can sustain that can damage his reproductive tract to the extent that he is not capable of successfully breeding.
Reproductive tract problems
Persistent frenulum: A thin band of tissue, or frenulum, connects the penis to the prepuce of a bull at birth. This band of tissue normally disintegrates by about one year of age, but in some yearling bulls it is still present at the start of their first breeding season. A persistent frenulum will pull the penis into a rainbow shape and will prevent breeding. Correction of this problem can be achieved with a simple surgery.
Penile hair ring: Body hair can accumulate on the penis due to riding activity. This hair can gather into a ring near the end of the penis. In some cases the ring can cause enough constriction to severely damage the penis. This condition can be discovered by routine examination of the penis during a breeding soundness examination (also referred to as a BSE). Treatment consists of removing the hair ring, but if damage is extensive, the bull may not return to service.
Preputial lacerations with prolapse of the prepuce: The prepuce can be lacerated during mating or from damage to the sheath. The deeper the laceration, the more serious the prognosis. Superficial tears will commonly heal with only 30 days sexual rest.
Hematoma of the penis: This condition is often referred to as a broken penis, but it is actually a tear in the fibrous, elastic layers that surround the penis. The bull will have a swelling immediately in front of the scrotum. This swelling is due to blood forming a clot around the penis. The injury occurs during mating and is considered very serious.
Deviations of the penis
Earlier trauma can cause deviations of the penis after the initial damage has healed. Laceration of the prepuce or hematoma of the penis can cause scar tissue to form between the penis and the prepuce, which can produce a deviation.
Spontaneous deviations are due to an abnormality of the fibrous ligament that runs along the top of the penis. This ligament is supposed to keep the penis relatively straight during erection. Three types of deviations can occur. They are:
Spiral: The most common of this group is a spiral deviation, which occurs when the ligament slips off to the left side of the penis causing a counterclockwise spiral. A similar condition is commonly seen when using an electroejaculator to collect semen samples. But it is not considered a problem unless it occurs in natural breeding situations.
Ventral: If the ligament along the top of the penis is thin and stretched, it cannot hold up the end of the penis, and the penis takes on a rainbow shape.
S-shaped: The S-shaped deviation occurs in older bulls with an excessively long penis. The ligament along the top of the penis is strong enough but is too short. Therefore, during an erection, the penis is pulled into an S-shape.
Surgical correction has been described for spiral and ventral deviations, but long-term return to breeding is not expected.
Each of these injuries to the penis or prepuce can cause an otherwise fertile bull to fail to impregnate cows.