Livestock Management
April 2007*
LM-17
Bull Power:
Examination of Beef Cattle Bulls for Breeding Soundness
Brad R. LeaMaster and Michael W. DuPonte1
1
Department of Human Nutrition, Food and Animal Sciences
T he evaluation of bulls for breeding soundness is an
effective and reliable way to identify bulls that are
potentially poor breeders. This management technique
ability to breed, testicular size as measured by scrotal
circumference, and semen quality and quantity. Any
physical defect or continuous lack of libido that interferes
can be used to greatest advantage if culling occurs before with the desire and ability of the bull to breed results in
bulls are turned out with females. Also, the evaluation is that animal being considered as unsatisfactory, even if
an important means available to the producer for predict- he has satisfactory testicular development and seminal
ing bulls with satisfactory to excellent potential. This characteristics. A complete BSE examination should
information can then be used to select superior bulls for include the following components:
a larger number of females, which thereby improves the 1. Physical examination for abnormalities that could
efficiency of production. A breeding soundness evalua- interfere with the desire and ability of the bull to breed.
tion (BSE) provides an opportunity to select against low The bull should be observed while he is walking on a
fertility as well as to improve fertility in both males and hard surface. Any lameness or locomotor problem that
females. It has been shown that bulls with large testicles could impair mating ability should be noted. It is not
at an early age tend to have male offspring with larger practical to carry out a complete clinical examination
testicles and female offspring that are more fertile than of every system in the body during a BSE; however, the
progeny from bulls with small testicles. The general bull must have good eyesight and be in good health.
bull population is made up of several breeds of bulls of 2. Libido, or sex drive, is an important and often
varying ages and sizes. There are large differences in the overlooked component of breeding evaluations. Studies
reproductive capacities among bulls of the same breed have shown that libido in a yard test is highly correlated
and age or weight. Fertility ranges from sterile and sub with serving capacity in the pasture, and that almost 10%
fertile to highly fertile within all breeds. Generally, about of bulls could be culled because of inadequate libido.
one or two bulls in five in an unselected population are Because libido is heritable (0.59), a serving capacity test
not satisfactory because of inadequate semen quality, also offers the opportunity to reduce the incidence of this
problems that prevent copulation, or lack of libido (sex undesirable trait in bull populations. Unfortunately, this
drive). The highest incidence of satisfactory bulls is ingredient of the BSE is the most difficult and inconve-
found between two and three years of age. nient to evaluate, and often does not receive adequate
attention from the producer or veterinarian.
What is a breeding soundness evaluation? 3. Examination of the genital organs should be a
A breeding soundness evaluation is a prediction of a part of the BSE and include inspecting the penis for
bull’s potential reproductive capacity based on standard physical defects that could impair or prevent copulation.
measurements and interpretations of certain selection Scrotal and testicular palpation should be conducted to
criteria that are related to the desire and ability to breed
and to fertility based on measurements of testicular Originally published in 1995 as Hawaii Animal Health Series Fact
development and certain seminal characteristics. The Sheet #95-2; reissued with minor revisions. Brad LeaMaster is a for-
BSE includes an assessment of the libido and physical mer veterinarian with the CTAHR Department of Animal Sciences.
Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in coopera
tion with the U.S. Department of Agriculture. Andrew G. Hashimoto, Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mänoa, Honolulu, Hawai‘i 96822.
An equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, age, religion, color, national origin, ancestry, dis
ability, marital status, arrest and court record, sexual orientation, or status as a covered veteran. CTAHR publications can be found on the Web site <http://www.ctahr.hawaii.edu/freepubs>.
UH–CTAHR Bull Power: LM-17 — Apr. 2007
detect any abnormalities which might have an effect on Occasionally, a producer conducts a BSE during the
fertility. Common abnormalities include small testicles, breeding season to determine if the sire is keeping his
soft testicles, difference in the size of testicles, scrotal sperm production up while breeding the herd. Evaluation
hernia, scrotal dermatitis, cryptorchids (high flankers), is done after three to four weeks into the breeding season.
and palpable epididymal conditions. By this time all females should have been in estrus, and
A rectal examination should be performed by a vet- the bull should have had the opportunity of breeding
erinarian and include palpation of the pelvic urethra, each. The presence of poor quality semen at this time
prostrate, vesicular glands, ampullae, vas deferens, and would indicate overuse. The bull should be rested and a
internal inguinal rings. The most common abnormal replacement selected.
finding associated with the internal genital organs is A BSE at the end of the breeding season is of little
seminal vesiculitis. value to the current breeding season; however, it does
4. Scrotal circumference measurement is easy to allow the producer an opportunity to eliminate any un-
perform and contributes important information to the desirable bulls so they will not be carried over several
BSE. Bulls with a large scrotal circumference (as a months without any economic return.
reflection of large testicles) produce more semen, have Bulls may be tested anytime there may be a doubt
a higher prevalence of normal sperm, and have greater or question regarding a bull’s fertility. For example,
sperm motility than bulls with small scrotal circumfer- if females continue to recycle, indicating they are not
ence. In beef cattle, there is a high correlation between bred, then the bull that is supposed to be breeding them
scrotal circumference measurements in bulls and the age should be examined. This could be done at any time the
at which female progeny reach puberty. Females from producer desires, with adjustments made accordingly.
sires with above average testicle size reach puberty at an A veterinarian is not required to be present for all of
earlier age. Selection based on scrotal circumference of- the segments of the BSE. For example, the evaluation
fers another opportunity to improve fertility in herds. of the social interaction of the bull among other bulls
5. Semen evaluation. Sperm motility and morphol- and its libido and ability to breed can be done by the
ogy are the seminal characteristics that are most highly producer, thereby saving money.
correlated with fertility and are the most easily repeated.
Characteristics such as volume, concentration, and Benefits of a BSE
percentage alive are no longer used as scoring criteria Research studies have shown that when bulls were given
because there is a low correlation with fertility and be- a BSE prior to breeding, as compared to none in previous
cause repeatability within bulls and between ejaculates years, the pregnancy rate increased by 3.5%, the breeding
is poor, especially in electroejaculated samples. season was shortened, calf weaning weights increased,
and the bull-to-cow ratio increased from 1:20 to 1:30.
When to evaluate bulls
Sires may be evaluated at any number of times and as References
often as desired. Evaluation just prior to the breeding Sorensen, A.M. 1979. Animal reproduction principles
season has the advantage that the evaluation indicates and practices. McGraw-Hill Book Company, New
breeding ability at the time nearest the time of use. Males York. p. 110–146.
are normally gathered at this time for observation, so un- Radostits, O.M., K.E. Leslie, and J. Fetrow. 1994.
necessary labor and stress are eliminated. A disadvantage Planned animal health and production in beef cattle
of testing just prior to the breeding season is acquiring breeding herds. In: Herd health: Food animal pro-
replacements. If several bulls are unsatisfactory it may duction medicine. 2nd edition. W.B. Saunders Com-
be difficult to find replacements of the desired quality. pany, Philadelphia. p. 331–393.
Evaluation during the off season when bulls are plenti-
ful offers an excellent opportunity to purchase new sires. Acknowledgement
Prices should be best at this time. The disadvantage is The authors extend their thanks and appreciation to Mr.
that the bull selected may injure himself or become Victor Groves for graphics and technical services.
sick between the time of evaluation and the breeding
season.
2
UH–CTAHR Examination of Beef Cattle Bulls for Breeding Soundness LM-17 — Apr. 2007
Table 1. Sample BSE scoring system
Scrotal circumference (cm)
Age (months)
Rating 12–14 15–20 21–30 >30 Score
Good >35 >37 >39 >40 40
Fair 30–35 31–37 32–39 33–40 24
Poor <30 <31 <32 <33 10
Sperm motility
Rating Gross Individual Score
Very good Vigorous swirls Rapid, straight 20
Good Slow swirls Moderate, straight 12
Fair No swirls, some oscillation Slow, straight 10
Poor Little movement, sporadic oscillation Very slow, erratic 3
Sperm morphology
Rating Primary abnormalities Total abnormalities Score
Very good <10 <25 40
Good 10-19 26-39 24
Fair 20-29 40-59 10
Poor >29 >59 3
The scores for the three categories are summed. If the total score is 60 points or more, the bull will probably be a satisfactory
breeder; if the score is 30 or less, the bull classifies as unsatisfactory; and if the score is between 30 and 60 the bull is
classified as a questionable potential breeder. Judgment must be used in interpreting the score. If a bull scores high on two
criteria but has a serious problem with the third, the bull should be classified as a questionable potential breeder, even if the
score is above 60 points. The score should be used only as a guide to assist in making intelligent management decisions.
