There is a saying regarding bull selection: "Visual analysis tells you what a bull appears to be. His pedigree tells you what he ought to be. His performance and progeny tests tell you what he actually is."
You should consider several factors when selecting a bull for your operation: breed, size, desirable traits, complementarity in a crossbreeding program and marketing strategy for the offspring. From an economic standpoint, reproduction is 10 times as important as carcass quality and 5 times as important as growth rate.
In recent years, frame size has been emphasized as a desirable trait. The economic value of greater than average frame size to the commercial cattle producer is questionable. Martin Jorgensen of Ideal, South Dakota, who has been feeding, processing and marketing beef through his own branded beef program for the last several years, stated that, "An inch of height is worth about $.03 and an inch of thickness is worth about $50 per head." As a commercial beef producer, you are in business to sell pounds of red meat, not inches of height and bone.
You select and purchase bulls for genetic improvements that will help you achieve the goals of your breeding program. Research indicates that as much as 80-90% of the progress made in a breeding program comes through proper bull selection. If natural service is used, each bull should sire approximately 25 calves per breeding season. If artificial insemination is used, one bull could theoretically sire all of the calves produced by your herd in a given breeding season.
The average female only produces one calf per year, having very little genetic impact on the herd.
The best way to evaluate the potential genetic value of a bull is through a sound set of performance records and the use of expected progeny differences (EPDs). EPDs allow us to do a more accurate job of comparing bulls within breeds than previous methods.
You should first determine the current strengths and weaknesses of your cow herd. Next, establish some specifications for the traits you want in the bulls you ultimately select (e.g., birth weight, weaning weight, yearling weight, milk production, etc.). Then consult the sire summaries of the breeds you are interested in and select the sires that meet these specifications.
Figure 1. Three scrotal shapes commonly seen in beef bulls. They are the straight-sided scotum (A), the normal scrotum (B) and the wedge-shaped scotum (C). Scrotal shape B is the most desirable. (Coulter 1987).
Expected progeny differences (EPDs) are used to estimate how the future progeny of a bull will compare to the progeny of other bulls within a particular breed. EPDs are reported in pounds for birth weight, weaning weight, yearling weight, maternal weaning weight and maternal milk production. Scrotal circumference EPDs are given in centimeters.
Each bull listed in a breed's sire evaluation report is compared to all the other bulls listed. For example, Bull A has an EPD for yearling weight of +30 pounds with an accuracy value of 0.80 and Bull B has an EPD for yearling weight of +5 pounds with a similar accuracy value. If these two bulls are bred to enough cows in your herd, you could expect Bull A's progeny to have a +25 pound advantage in yearling weight over Bull B's progeny.
The information used to calculate an EPD may be based on any combination of: individual performance, pedigree and progeny and grand progeny performance information. In addition, sire EPDs are more accurate than anything previously available because they account for the following factors:
1) Genetic value of cows a bull is bred to
2) Environmental differences affecting contemporary groups
3) Quality of other sires in the contemporary group
4) Genetic trend.
Once a bull has progeny, less emphasis is placed on the less quantitative pedigree information. The sire's own performance and the performance records of his progeny become the major determinants of the EPD.
Accuracy values indicate the predictability of EPDs and are an abbreviated method of expressing an EPDs reliability. Accuracy values range from 0.0 to 1.0. As accuracy approaches 1.0, the EPD is more reliable and can be expected to change less in the future as more progeny data are accumulated.
Accuracy may be categorized into low, medium and high reliability as follows: low, 0.0-0.50; medium, 0.51-0.75; high, 0.76-1.0. EPDs are used to decide which bulls are selected while accuracy values suggest how extensively the bulls should be used. Bulls with favorable EPD values and correspondingly high accuracy values can be used with the confidence that they will genetically improve the herd.
Once you have selected a bull with the desired genetics, you must be sure that this bull is capable of causing pregnancy in a cow herd. Each and every bull needs to have a breeding soundness evaluation (BSE) every year, 30-60 days before the start of the breeding season. It has been reported that more than 10% of yearling bulls are either sterile or subfertile and 4% of proven sires develop serious fertility problems between breeding seasons. To reduce the likelihood of introducing venereal diseases into your herd, we recommend that you purchase virgin bulls.
Much of the material in the following discussion of the breeding soundness evaluation comes from the Beef Improvement Federation's Guidelines for Uniform Beef Improvement Programs.
Examining bulls for breeding soundness before the breeding season will detect most bulls with potential fertility problems. This examination should be performed by a veterinarian who has had significant experience in bovine herd health and fertility evaluation of bulls, or by other experienced, competent personnel. However, even with the best personnel, current techniques cannot accurately predict degrees of fertility. BSEs are really a screening process used to assess probable bull fertility. Results from an actual breeding season remain the only true test of a bull's fertility.
1. Physical examination. Do this before collecting semen. This will cull bulls with undesirable physical characteristics or abnormalities before you make useless attempts at collection.
a) Palpate scrotum and testes.Bulls having a normally shaped scrotum with a distinct neck generally have the best testicular development (Figure 1, Bull B). Testes are located in the scrotum because sperm can only be produced within a narrow temperature range, several degrees cooler than internal body temperature. Normal scrotal anatomy permits effective temperature regulation.
Bulls with straight-sided scrotums often have only moderate testicle sizes (Figure 1, Bull A). The straight-sided neck of the scrotum is generally due to fat deposits that will probably impair proper thermoregulation, particularly in the summer. As bulls mature and lose fat, they often develop a more normal-shaped scrotum.
Wedge-shaped scrotums are pointed towards the bottom and tend to hold the testes close to the body wall (Figure 1, Bull C). Bulls with this scrotal configuration have undersized testes that seldom produce semen of adequate quality. Bulls with wedge-shaped scrotums should be avoided.
Palpate the scrotum and testicles, noting position and consistency. This should be done by an individual who can properly evaluate testicular tone as it relates to testicular function. Deviations from normal testicles vary from extremely fibrotic to a soft, flaccid consistency. Conditions such as testicular degeneration or hypolasia (atrophy) and orchitis (inflammation of the testis) affect the consistency and size of the testicles and result in abnormal sperm production. During severe winters, it is not uncommon for a bull's scrotum to become severely frostbitten or frozen with a resultant decrease in fertility.
b) Rectally examine accessory sex glands. This is an examination of the reproductive organs located in the pelvic region. Abnormalities of the accessory sex organs (prostate, seminal vesicles, ampullae and ductus deferens) are not uncommon and are often accompanied by poor semen quality. If an active inflammatory process is present, white blood cells will be found in the ejaculate, varying from a few to almost 100% of the sample.
c) Examine extended penis and prepuce. The external genitalia should be examined with great care; the penis is palpated through the external sheath and by protruding it manually. Prolapse of the prepuce is occasionally found, more often in the Brahman and Brahman-derived breeds. Unless there are lesions on the prolapsed membrane, the prolapse does not interfere with mating. However, the exposed membrane is predisposed to injuries.
At this time, you may take diagnostic preputial samples to determine the presence or absence of campylobacteriosis or tricho-moniasis. The penis and prepuce should be examined for any structural abnormalities or adhesions when the semen sample is collected.
Upon erection, the penis should come from the sheath in a straight line with the body of the bull. In Australia a defect called "spiral deviation of the penis" has been identified (Coulter 1987). A report from Australia indicates that bulls in 60% of herds examined were affected, and that 1% of horned bulls and 16% of polled bulls had the defect. This condition results in a significant reduction in the bull's ability to service cows because he cannot accomplish insertion. In bulls where 100% of their mounts were affected, pregnancy rates were as low as 3%. Spiral penile deviation is probably just as prevalent in North America.
Spiral deviations are usually found in bulls 3-6 years old. This condition cannot be diagnosed at the time of electroejaculation. In fact, electroejaculation can induce a similar deviation of the penis that may not occur at all during natural service. Watch the breeding activity of your bulls to make sure they do not have this defect. Spiral deviation is moderately heritable. It can be diagnosed by allowing a bull to mount several estrus-synchronized heifers and carefully observing the results.
Record any injury or abnormality as acceptable or unacceptable. If the bull is unacceptable, have the examiner explain why. Bulls with gross deficiencies or abnormalities detected by physical examination should be culled.
2. Scrotal circumference. Scrotal circumference and testicular size are directly related to sperm production in dairy and beef bulls. Since the testicles are composed of 75-80% seminiferous epithelial cells and these cells form spermatozoa, it is logical that the larger the testicles, the greater the bull's ability to produce sperm and produce pregnancies. In addition, bulls with small testicles tend to produce a higher percentage of abnormal sperm.
As the scrotal circumference increases, motility and percent normal sperm increase and sperm abnormalities decrease. Scrotal circumference has been shown to be a more accurate predictor of when a bull reaches puberty than either age or weight, regardless of breed or breed cross (i.e., an average of 27.9 cm.). Yearling bulls should have a scrotal circumference of at least 30 cm.
Record the actual measurement of scrotal circumference in centimeters, and age of the bull at time of measurement.
Scrotal circumference is highly heritable and has a high positive genetic correlation to age of puberty of the bull's daughters. Studies have shown that for each additional 4.0 cm. of scrotal circumference above the breed or herd average, one can expect a 1.0 cm. increase in the scrotal circumference of male offspring and 15.44 days earlier puberty in female offspring. The use of a sire with above average testicular size (scrotal circumference) for his age and breed will result in female progeny that reach puberty at a younger age, cycle more regularly and consequently have greater potential lifetime productivity.
Scrotal circumference is the most useful linear measurement currently taken on beef cattle.
3. Semen evaluation. Under field conditions, the semen sample is usually collected by electroejaculation. All bulls do not respond well to the electroejaculator, and may not produce representative samples.
The two most important things to look for in the semen are the proportion of sperm that are motile and the structure or morphology of the sperm. Procedures for scoring motility and morphology are found in the Proceedings of the 1976 Annual Meeting of the Society of Theriogenology. A third factor, the concentration of sperm in an ejaculate, may not be accurately measured when the semen sample is collected by electroejaculation.
A semen sample should only be evaluated for motility under field conditions if the temperature of the sample has been kept constant from the time of collection until the time of examination under the microscope. Small portable slide warmers are available for this purpose. The presence of urine in the sample will greatly reduce motility. Heat, cold or chemical contamination of the collection apparatus can immobilize spermatozoa.
The appearance of an increased number of abnormal sperm in the ejaculate is a reflection of lesions of the testes and/or the excurrent duct system. Some sperm abnormalities (e.g., acrosomal and nuclear) are heritable and bulls exhibiting these abnormalities should be culled. A bull should have no more than 20% abnormal sperm. If a bull has a sperm abnormality greater than 80%, he will probably be infertile.
The scoring system for predicting potential breeding soundness of bulls prepared by the Society of Theriogenology (1976) incorporates scrotal circumference, sperm motility, and sperm morphology (Table 1). New and better scoring systems are likely to emerge over time from the Society and other sources and we recommend their use.
The results of semen evaluation of beef bulls 11-13 months old are often difficult to interpret. For example, semen quality in young bulls has been shown to improve, often dramatically, for up to 16 weeks following the onset of puberty. Test the semen of young bulls at 15 or 16 months of age to avoid the potential early culling of a bull that may have adequate semen quality 2 months later. Positive results from a semen evaluation, even in yearling bulls, indicate a moderate to high probability of acceptable fertility, while negative results are not conclusive, particularly if the bulls involved are young or sexually rested. Reevaluate bulls with poor semen quality every 3-4 weeks. If the results do not improve, you can be fairly sure that the bull is infertile and should be culled. All bulls should be tested before every breeding season as injuries or other problems may have reduced the bull's semen quality since the previous evaluation. A breeding soundness evaluation performed by a veterinarian usually costs $25-35 per bull.
Morphology2 |
Scrotal circumference3 |
Scoring System4 | ||||||||||
Classification |
Motility Score |
Primary abnormalities |
Total abnormalities |
Score |
12-14 months old |
15-20 months old |
21-30 months old |
30+ months old |
Score |
Motility |
Morphology |
Scrotal circumference |
No. |
Percent |
Percent |
No. |
Cm. |
Cm. |
Cm. |
Cm. |
No. |
Score No. |
Score No. |
Score No. | |
Very good |
20 |
10 |
25 |
40 |
35 |
37 |
39 |
40 |
40 |
20 |
40 |
40 |
Good |
12 |
10-19 |
26-39 |
24 |
30-35 |
31-37 |
32-39 |
33-40 |
40 |
12 |
24 |
24 |
Fair |
10 |
20-29 |
40-59 |
10 |
-- |
-- |
-- |
-- |
-- |
10 |
10 |
-- |
Poor |
3 |
29 |
60 |
3 |
30 |
31 |
32 |
33 |
10 |
3 |
3 |
10 |
Source: Beef Improvement Federation 1990.
1Examination as recommended by Society for Theriogenology, revised, September 1976.
2Spheriods: Less than 05/HP field = Occasional = +05% primary abnormality
05/ to 15/HP field = Few = +15% primary abnormality
15/ to 25/HP field = Many = +25% primary abnormality
+25/HP field = Multitudes = +35% primary abnormality.
3Scrotal circumference data based on data from Angus, Charolais, Hereford, and Simmental breeds.
4Based on scoring system totals, satisfactory potential breeder has 60-100 points; questionable potential breeder has 30-59 points; and unsatisfactory potential breeder has 0-29 points.
1. Body condition. Bulls should have enough body condition to be strong with some reserves of energy in the form of fat. Overfat bulls have decreased fertility and decreased stamina for mounting and seeking cows in heat. A Canadian study reported that feeding high energy diets to young Hereford bulls damaged their sperm producing ability to the extent that several bulls in the study were sterile.
2. Feet, legs and joints. Good feet and legs are essential if a bull is to travel long distances over rough terrain and service cows successfully. Particular attention should be given to the manner in which the bull moves. The stride should be free with no signs of lameness. Abnormal conformation of the rear limbs (i.e., sickle-hocks and post-legged) is especially detrimental to the bull used in natural service. Long hooves and corns should be trimmed 4-6 weeks before the breeding season.
3. Eyes. Pinkeye or cancer eye hinder a bull's vision and reduce his breeding effectiveness. Bulls that are blind in one eye present a danger to the people handling them and to cows they are attempting to service.
4. Pelvic measurements. Some purebred breeders perform pelvic measurements on yearling bulls because of this trait's high heritability (50-55%). The hypothesis is that bulls with larger pelvic areas will sire daughters with larger pelvic areas which should result in a reduction in calving difficulty. However, pelvic measurements and other physical measurements (e.g., pelvic slope) have generally served as poor predictors of calving difficulty.
As a general rule, larger-framed cattle have larger pelvic areas and also produce calves with heavier birth weights. Calf birth weight and age of dam at calving are the most important factors affecting calving difficulty.
5. Libido. Libido, or sexual activity, and semen production in bulls apparently have no relationship, so it is possible to get good semen from bulls with low libido and vice versa.
Mickelsen (1990) observed that the serving capacity of a group of bulls is positively correlated with the proportion of cows exhibiting estrus in a herd. He cited a study in which mounting activity was recorded for 7 1/2 hours when bulls, in groups of 3, were put with 114 head of heifers. Bulls in the high serving capacity group (10.3 services/bull) had an 81% first-service conception rate compared to 56.7% for the bulls in the low serving capacity group (2.3 services/bull).
Studies have shown that both a low number of services and a very high number of services were associated with poor fertility. Low numbers or no services during testing is likely predictive of low breeding activity under field conditions. Very high serving activity may have resulted in the depletion of sperm reserves.
Differences in libido in bulls are due to genetic as well as environmental factors. Several studies have shown that the dominant bulls in a group often sire the largest number of calves (Mickelsen 1990). However, if the dominant bulls happen to be subfertile, this could actually result in a reduced number of pregnant females. In a group of bulls with varying ages, social ranking affects a bull's serving capacity. Therefore, do not mix yearling and 2-year-old bulls with older bulls.
In most parts of the country, the typical bull-to-female ratios used by cow-calf producers are from 1:15 to 1:30. Increasing the efficiency of natural mating offers enormous potential for lowering the costs of production.
Colorado State University recently completed a study designed to determine the optimal bull-to-female ratio required for maximum reproductive performance on both estrus synchronized and naturally cycling heifers. Four treatments were used : treatment 1 included 200 nonsynchronized heifers and 2 bulls/100 heifers (bull-to-female ratio of 1:50); treatment 2 involved 200 synchronized heifers and 2 bulls/100 heifers (bull-to-female ratio of 1:50); treatment 3 involved 200 synchronized heifers and 4 bulls/100 heifers (bull-to-female ratio of 1:25) and treatment 4 involved 200 synchronized heifers and 6 bulls/100 heifers (bull-to-female ratio of 1:16). Total length of the breeding season was 28 days.
Results of this study indicate that the costs of production can be reduced by lowering the bull-to-female ratio. Treatment 1 (2 bulls/100 naturally cycling heifers) resulted in an 82% pregnancy rate. However, the results of this study also indicate that there is a limit to how far bulls can be extended when utilizing estrus synchronization. Treatment 2 (2 bulls/100 synchronized heifers) had a 77% pregnancy rate. Treatments 3 (1:25) and 4 (1:16), both synchronized, resulted in pregnancy rates of 83% and 84%, respectively. Treatment 4 had a 3-day advantage of day of conception compared to treatment 3.
The bull cost per pregnant heifer was calculated using the following assumptions. Yearling bulls, purchased for $1750, would be used for 4 breeding seasons before being sold for $800. This resulted in an annual depreciation cost of $238 ($1750 - $800 = $950 ÷ 4). Annual feed costs were $200, veterinary costs were $25 and there was an opportunity cost on the investment of $102 ($1750 + $800 = $2550 ÷ 2 = $1275 x 0.08). This is a total bull cost of $565 per year.
Table 2 shows the effect of different bull-to-female ratios on bull costs per pregnant heifer. The cost of estrus synchronization in this study was $3.70 per heifer, and is not included in the bull cost per pregnant heifer figures.
The results of this study indicate that most ranchers could lower the bull-to-female ratio used, maintain their herd's productivity and lower their bull costs per pregnant female. However, if you use a lower bull-to-female ratio, a breeding soundness examination performed 30-60 days before the breeding season is critical to success.
The Colorado researchers are planning to repeat this experiment, but will use artificial insemination (AI) instead of natural mating in the 1:16 bull-to-female ratio treatment. The use of AI has the potential of reducing the breeding costs even more than lowering the bull-to-female ratio.
Table 2. Bull Cost Per Heifer.Treatment
Treatment |
Bull - to - Female ratio |
Bull cost hfr. exposed* |
Pregnancy rate |
Bull cost / pregnant hfr.** |
Nonsynchronized 1 |
1:50 |
$11.30 |
82% |
$13.78 |
Synchronized 2 |
1:50 |
$11.30 |
77% |
$14.68 |
3 |
1:25 |
$22.60 |
83% |
$27.23 |
4 |
1:16 |
$35.31 |
84% |
$42.04 |
* Bull cost/hfr. exposed equals total bull cost/yr. divided by the number of females exposed (e.g., $565 ÷ 50 hfrs. = $11.30).
** Bull cost/ hfr. pregnant equals bull cost/hfr. exposed divided by the pregnancy rate (e.g., $11.30 ÷ 0.82 = $13.78).
Source: Healy, et al. 1990
While natural service is, and probably will remain, the primary form of breeding in most cow-calf operations, increasing the use of artificial insemination (AI) may increase genetic improvements. For the commercial cow-calf producer, a good place to begin using AI is in breeding yearling replacement heifers. These heifers are usually fed and handled separately from the mature cow herd and you do not have to deal with the added complication of nursing calves.
The use of AI offers the following advantages to both purebred and commercial cow-calf breeders:
1. It should reduce the bull cost per pregnant female; eliminates the year-round expense and hassle of keeping and handling bulls. AI may not completely eliminate the use of natural breeding. You may still need clean-up bulls, but the total number of bulls required will be reduced.
2. You can use outstanding, proven bulls at modest prices and get maximum genetic improvements in your herd. In three generations, 87.5% of the genetics of your herd trace back to the sires of those three generations.
3. By using superior AI bulls, you can rapidly improve the economically important traits of calving ease, weaning weight, average daily gain, carcass quality and maternal ability.
4. The risk of introducing harmful recessive traits, such as dwarfism, double muscling, mule foot or marble bone is significantly reduced due to thorough sire selection and progeny testing.
5. Using AI usually results in an improved level of management because more complete records are kept. This improves replacement heifer selection and production and feeding management.
6. The calving season can be shortened, resulting in a heavier and more uniform calf crop.
7. Venereal diseases cannot be introduced or transmitted when using disease-free semen.
References
American Breeders Service. "AI Management Manual." Division of S.R. Grace & Company. DeForest, Wisconsin. 1983.
Beef Improvement Federation. Guidelines for Uniform Beef Improvement Programs. Sixth edition. Oklahoma State University, Stillwater, Oklahoma. May 1990.
Brinks, James S. "Scrotal Circumference and Its Potential Usefulness." Angus Journal. February 1985.
Brownson, Roger. "Breeding Soundness Examination of Beef Bulls." Angus Journal. April 1985.
Coulter, Glenn H. "Evaluating and Managing the Herdsire for Reproduction." Agriculture Canada Research Station, Lethbridge, Alberta. 1987.
Healy, V.M., G.W. Boyd, R.G. Mortimer and J.R. Piotrowski. "Lowering Production Cost: Investigating the Optimal Use of Bull Power." National Conference: Lowering Beef Cattle Production Costs. Colorado State University, Fort Collins, Colorado. October 5-6, 1990.
Mickelsen, W. Duane. "Breeding Soundness Examination of the Bull: Fact or Fiction." Unpublished paper. School of Veterinary Medicine. Washington State University, Pullman, Washington. 1990.
Merck Veterinary Manual. "Breeding Soundness Examination of the Male." Sixth edition. Edited by Clarence M. Fraser, et al. Merck & Co., Inc. Rahway, New Jersey. 1986.
Proceedings of the 1976 Annual Meeting of the Society of Theriogenology. Society of Theriogenology, Association Building, 9th and Minnesota, Hastings, NE 68901
Ott, Randall S. "Breeding Soundness Examination of the Bull: Semen Collection and Evaluation." Illinois Professional Topics. 9:3. 1983.
Donald D. Nelson is an Extension Beef Specialist at Washington State University.
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