Bulls for breeding
A bull's main function in a profitable breeding operation is to get a high proportion of cows in calf early, during a mating period of nine weeks or less. To achieve this bulls must be sound for breeding, they must be willing and able to serve a high percentage of cows on heat and they must be free of any abnormalities of the penis, testicles, feet and legs. Unfortunately a substantial proportion of both young and old bulls in Victoria are not sound for breeding. While it is rare to find bulls that are completely infertile, bulls with abnormalities that reduce their fertility are quite common. In one Victorian study of 643 young bulls aged 15-24 months, 18.6% had abnormalities that would reduce their fertility. The most frequent abnormalities were low serving capacity, testicle problems and damaged penises (see table 1 ).
Table 1. Abnormalities detected in young bulls. (Blockey - unpublished data)
|No. of bulls examined||Incidence of abnormalities|
|Low serving capacity||Small and/or soft testicles||Penis damage||Total|
A further survey of 447 herd bulls aged from three to 11 years for breeding soundness, from four different properties, showed that 136 (30.4%) of these bulls had problems that would lower fertility. These problems are shown in Table 2.
Examination for breeding soundness
Almost all bulls that are unsound for breeding can be detected during an examination for breeding soundness. This consists of a physical examination of testicles, legs and feet while the bull is restrained in a crush, and a serving capacity test to measure a bull's serving capacity and to detect penis abnormalities and signs of arthritis.
Testicle size and consistency
The circumference of the scrotum is the best indicator of testicle size. The head and tail of the epididymis, which are the storage areas on the top and bottom of each testicle, are also examined for abnormalities.
Examination of the peni
The most common injury that occurs to the penis is a 'broken penis'. This usually occurs if the cow collapses under the bull or if the bull's legs go from under him at the time of service. While the penis does not actually break it gets bent out of line, causing massive haemorrhaging into the surrounding tissue of the sheath. After the injury the bull is not inclined to serve. As the injury heals, adhesions usually develop that prevent the protrusion of the penis. The end result is that the bull is usually not capable of serving again.
Table 2. Abnormalitites detected in herd bulls. (Blockey - unpublished data)
|Incidence of abnormalities|
|No. of bulls examined||Low serving capacity||Arthritis or deviation||Penis damage||Over-grown claws||Small and/or
The cause may be put down to bad luck; however, poor dexterity of the bull as a result of poor feet placement, lameness caused by overgrown hooves or corns, and arthritis of the joints are considered to be predisposing factors. Watching a bull serve or palpation of the penis through the sheath will detect swelling and scar tissue that indicate injury. Deviation of the penis can occur because of some irregularity in the development of the penis. Spiral deviation of the penis or 'corkscrew penis' is the condition where the end of the penis twists into a spiral, or corkscrew shape as the bull attempts to serve. The condition develops with age and has a higher reported incidence in poll breeds. It is rarely observed in bulls at two years old, but once a bull's penis starts to spiral, the condition occurs more frequently until eventually it happens at every service, and of course service is virtually impossible.
More than 25% of surveyed poll breed bulls culled at five years of age were culled because of corkscrew penis. Observing service is the only sure means of detecting the problem and its increasing incidence with age makes it worthwhile to examine bulls each year before joining, using the serving capacity test.
Examination of legs
The legs of a bull have a number of functions. Of these walking and load bearing are the most obvious, but all limbs need to be efficient shock absorbers as well. A survey of 900 herd bulls in Victoria showed that about half the bulls that are culled for being unsound for breeding have a leg or foot lameness. Hip arthritis, affecting bulls more than four years old, is by far the most common, with hock, knee, fetlock and stifle arthritis also common. Overgrown claws, foot abscesses and corns cause the foot lameness. These foot and leg lamenesses, together with poor serving capacity and penis problems, make the average working life of a bull only three seasons. The hind leg has a weight bearing and propulsion role in mounting the cow. Bones of the hind leg are set at an angle so that the muscles, tendons and ligaments can assist the bones and joints in absorbing the concussion that results when the bull places its weight on the hindquarters, whether standing, walking or serving a cow.
In the correct hind leg conformation a vertical line from the pins would just touch the hock and dewclaw (see Figure 1).
Figure 1. Correct stance
The angle between the ground and the pastern should be 50°-60°. If the angle is too great the bull appears to be walking on his toes and can wear the hoof excessively. If the angle is too small the bull appears to walk on the heel of the hoof, resulting in excessive claw growth.
When the hind leg is too straight (post-legged: that is, straight hocks) the joints absorb most of the concussion (see Figure 2).
Figure 2. Post-legged hind leg
The joints have a thin, sensitive lining which becomes eroded with the stress of this concussion. The hip joint especially absorbs a great deal of concussion because, being at the end of a series of joints, the concussion stops there. Avoid bulls with straight hindlegs.
Bulls with hind legs that are too curved (sickle-hocked) are more prone to penis injury caused by their rear legs slipping from underneath them during service. They also wear their heel low and are predisposed to lameness by stone bruising (see Figure3).
Figure 3. Sickle hocked stance
Hocks-in or hocks-out cause uneven weight bearing on the claws, which inevitably affects hoof growth (see Figure 4). Hocks-out are more structurally damaging than hocks in, causing persistent ligament damage. The front legs should be straight, from the pastern to the body of the bull, with the shoulder-blades angled away from the head at about 30° to the vertical. Avoid bulls with very straight pasterns in the foreleg as they are likely to develop arthritis of the knee.
Examination of feet
Excessive growth and curvature usually lead to lameness. The claws should be well shaped with little space between them, and their inner surfaces should be as close to parallel as possible. It is usual for the front hooves to point slightly outwards. If this angle is too great (toes out) or they point slightly inwards (toes in) it usually leads to excessive growth of either the inner or outer claw respectively. Toes twisting while walking can also cause uneven wear of the claws.
Figure 4. Examination of cattle stance
A common indicator of hip arthritis in bulls is the mis-shaping of the outside claw of a hind leg. The end of the claw grows upwards and resembles the start of a corkscrew. Wasting of the muscles about the hip joint often accompanies hip arthritis.
Viewed from behind a bull should pull his hind legs through, parallel to the direction of movement as he walks. He should not throw his legs inward or outward and the hind hoof should land in the print left by the front hoof. Post-legged and lame animals usually step short, whereas sickle-hocked animals commonly overstep, sometimes leading to stone damage of the pastern or dewclaw. About 50% of bulls with arthritis of the hip, knees, fetlock and back will show little or no lameness while walking around a yard. However, after repeated mounting and thrusting, as occurs in paddock mating or a serving capacity test, they will show signs of arthritis. In the case of hip arthritis the bull will favour the affected limb during mounting and thrusting. A bull with hip arthritis will drag its toe as the hind leg is brought forward in the step. Knee and fetlock arthritis is accompanied by difficulty in clasping the cow with the forelegs and, after that, lameness when chased around a yard. Older bulls that mount by placing their jaw on the cow's back and lever themselves up with an arched back are showing signs of back arthritis. Bulls with arthritis should be culled.
Serving capacity test
This test predicts the number of services a bull will achieve in the first three weeks of paddock mating. The accuracy of prediction is 90% and is based on the number of services the bull completes in a standard 20 minute or 40-minute yard test. There is a large difference between the performances of different bulls in this test.
The test is done as follows:
- non-oestrous heifers or cows are restrained in specially designed service crates which are located around the perimeter of a large yard. The females used in the test are selected carefully and managed to avoid any problems or injuries.
- bulls to be tested are sexually stimulated by allowing them to watch other bulls mount restrained females before the test.
- bulls are then allowed with the females for a 20 or 40-minute test. The number of services (not mounts) are counted and the bulls are observed for any abnormalities that might show up while serving.
As indicated in table 3, bulls of high serving capacity get a higher percentage of cows in calf on their first heat than bulls of medium or low serving capacity. Consequently herds mated to bulls of high serving capacity have a more compact calving spread.
They also have a higher pregnancy rate after a 10 week mating period.
Table 3. Relationship between a bull's serving capacity and herd fertility. (Blockey, 1978)
|Serving capacity (number of services in 20 min yard test)||Cows pregnant on their first heat
|Pregnancy rate after 10-week mating
|0.1 (low)||4 to 40||4 to 67|
|2 or 3 (medium)||55 to 65||89 to 93|
|4 to 7 (high)||62 to 78||90 to 100|
The author is indebted to Dr Mike Blockey for the research information referred to in this Agriculture Note.