Bull

The reproductive system of a bull

Bulls become fertile around seven months of age. Their fertility is closely related to the size of their testicles, and one simple test of fertility is to measure the circumference of the scrotum; a young bull is likely to be fertile once this reaches 28 centimetres (11 in); that of a fully adult bull may be over 40 centimetres (16 in).[10][11] Bulls have a fibroelastic penis. Given the small amount of erectile tissue, little enlargement occurs after erection. The penis is quite rigid when not erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of the retractor penis muscle and straightening of the sigmoid flexure.[12][13][14] Bulls are occasionally affected by a condition known as "corkscrew penis".[15][16] The penis of a mature bull is about 3–4 cm in diameter,[17][18][19][20] and 80–100 cm in length.[21] The bull's glans penis has a rounded and elongated shape.[21]

A common misconception widely repeated in depictions of bull behavior is that the color red angers bulls, inciting them to charge. In fact, like most mammals, cattle are red–green color blind. In bullfighting, the movement of the matador's cape, and not the color, provokes a reaction in the bull.[22][23]

Other than the few bulls needed for breeding, the vast majority of male cattle are castrated and slaughtered for meat before the age of three years, except where they are needed (castrated) as work oxen for haulage. Most of these beef animals are castrated as calves to reduce aggressive behavior and prevent unwanted mating,[24] although some are reared as uncastrated bull beef. A bull is typically ready for slaughter one or two months sooner than a castrated male or a female, and produces proportionately more and leaner muscle.[24]

Frame score is a useful way of describing the skeletal size of bulls and other cattle. Frame scores can be used as an aid to predict mature cattle sizes and aid in the selection of beef bulls. They are calculated from hip height and age. In sales catalogues, this measurement is frequently reported in addition to weight and other performance data such as estimated breed value.[25]

A bull paws up dust in a threat display

A warning sign for a bull-occupied field

Adult bulls may weigh between 500 and 1,000 kg (1,100 and 2,200 lb). Most are capable of aggressive behavior and require careful handling to ensure safety of humans and other animals. Those of dairy breeds may be more prone to aggression, while beef breeds are somewhat less aggressive, though beef breeds such as the Spanish Fighting Bull and related animals are also noted for aggressive tendencies, which are further encouraged by selective breeding.

An estimated 42% of all livestock-related fatalities in Canada are a result of bull attacks, and fewer than one in 20 victims of a bull attack survives.[26] Dairy breed bulls are particularly dangerous and unpredictable; the hazards of bull handling are a significant cause of injury and death for dairy farmers in some parts of the United States.[27][28][29] The need to move a bull in and out of its pen to cover cows exposes the handler to serious jeopardy of life and limb.[30] Being trampled, jammed against a wall, or gored by a bull was one of the most frequent causes of death in the dairy industry before 1940.[1] With regard to such risks, one popular farming magazine has suggested, "Handle the bull with a staff and take no chances. The gentle bull, not the vicious one, most often kills or maims his keeper".[31]

A bull with a nose ring that tethers him to a picket

In many areas, placing rings in bulls' noses to help control them is traditional. The ring is usually made of copper, and is inserted through a small hole cut in the septum of the nose. It is used by attaching a lead rope either directly to it or running through it from a head collar, or for more difficult bulls, a bull pole (or bull staff) may be used. This is a rigid pole about 1 m (3 ft) long with a clip at one end; this attaches to the ring and allows the bull both to be led and to be held away from his handler.

An aggressive bull may be kept confined in a bull pen, a robustly constructed shelter and pen, often with an arrangement to allow the bull to be fed without entering the pen. If an aggressive bull is allowed to graze outside, additional precautions may be needed to help avoid him harming people. One method is a bull mask, which either covers the bull's eyes completely, or restricts his vision to the ground immediately in front of him, so he cannot see his potential victim. Another method is to attach a length of chain to the bull's nose-ring, so that if he ducks his head to charge, he steps on the chain and is brought up short. Alternatively, the bull may be hobbled, or chained by his ring or by a collar to a solid object such as a ring fixed into the ground.

In larger pastures, particularly where a bull is kept with other cattle, the animals may simply be fed from a pickup truck or tractor, the vehicle itself providing some protection for the humans involved. Generally, bulls kept with cows tend to be less aggressive than those kept alone. In herd situations, cows with young calves are often more dangerous to humans. In the off season, multiple bulls may be kept together in a "bachelor herd".

Bullfighting

Many cattle ranches and stations run bulls with cows, and most dairy or beef farms traditionally had at least one, if not several, bulls for purposes of herd maintenance.[32][33] However, the problems associated with handling a bull (particularly where cows must be removed from his presence to be worked) has prompted many dairy farmers to restrict themselves to artificial insemination (AI) of the cows.[34] Semen is removed from the bulls and stored in canisters of liquid nitrogen, where it is kept until it can be sold, at which time it can be very profitable; in fact, many ranchers keep bulls specifically for this purpose. AI is also used to improve the quality of a herd, or to introduce an outcross of bloodlines. Some ranchers prefer to use AI to allow them to breed to several different bulls in a season or to breed their best stock to a higher-quality bull than they could afford to purchase outright. AI may also be used in conjunction with embryo transfer to allow cattle producers to add new breeding to their herds.