Bulls:

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Basic Strategies for Buying the Right Bull
Livestock Update, February 2007 by Dr. Scott P. Greiner, Extension Animal Scientist, Beef, VA Tech


As we move to the heart of bull buying season, the question is often asked- “which is the best bull in the sale?” The response to such a simple question cannot be painted with a broad brush, or in a manner which fits all needs. If we consider the question in the context “which is the right bull for my operation?” we are prompted to define the important parameters that need to be considered. Successful bull selection is dependent on effective strategies that allow the right bull to be identified.

Strategy 1: Define Herd Goals and Objectives, Identify Strengths and Weaknesses
Broad herd goals and objectives serve as the foundation for sire selection and provide guidance as to traits with the most economic relevance. A basic definition of the production and marketing system, along with management strategies and environment are key factors that warrant consideration:
Will the bull be used on heifers, mature cows, or both?

Will replacement females be retained in the herd?

How will the calf crop be marketed (at weaning?, backgrounded?, retained ownership? sell females?)

What are the labor and management resources available?

What are the feed resources and environmental conditions of the operation?

How will this sire contribute to the overall breeding system plan?
Within each of these considerations, an assessment of the strengths and weaknesses will provide more details. Fundamental records are key to identifying strengths and weaknesses. Basic performance parameters such as calving percentage, weaning percentage, weaning weights, sale weights, feed usage, etc. are necessary to serve as the basis for assessing areas of strength and those needing attention.
Strategy 2: Identify Priorities and Opportunities for Improvement
Priorities should be established based on those factors which stand to have the largest impact on profitability. Remember that income is derived from performance (sale weight, % calf crop weaned, carcass merit, etc.). Performance is a function of both genetics and environment/management. Superior genetics can be negated by poor management, which emphasizes the importance of delineating the impact of management (nutrition, health program) from that of genetics when specific priorities for the herd are established. As an example, operations marketing feeder cattle have a need for optimum early growth as calves are sold around weaning. This early growth is impacted by milk production of the dam, which in turn is influenced by available feed resources. Considering both the genetic and management influences on these traits is important.

Genetic improvement in commercial herds is largely accomplished through sire selection. Simplifying sire selection by focusing on the handful of priority traits is generally more achievable than attempting to change many traits simultaneously. Establishing the few traits to focus on is the key factor.


Strategy 3: Effectively Utilize Selection Tools
Once selection priorities have been established through close examination of herd goals and current status, a number of useful tools are at the disposal of beef producers to assist in making genetic improvement. Genetic differences across breeds have been well established, and utilization of different breeds in a complimentary fashion through structured crossbreeding plans provides the opportunity for improvement in multiple traits. Most importantly, heterosis attained through crossbreeding has been shown to have significant favorable impacts on traits such as reproductive efficiency and cow longevity which are critical for herd profitability. The limited ability to select for reproductive traits in the form of EPDs further emphasizes the importance of heterosis.

Individual EPDs are available for many traits of economic importance. The introduction of economic indexes which combine several related traits and their economic values into one EPD are available to assist with simultaneous improvement in multiple traits which impact areas such as carcass merit and post-weaning profit. Again, with the large number of EPD tools available, the critical step is to determine the EPDs which are most important and establish benchmarks relative to each. Several tools can be utilized to assist in the determination of EPD specifications. EPD values for current and past sires can be used as benchmarks. With these benchmarks, EPD specifications can be set to reflect the desired increase or moderation in performance for a particular trait.
Strategy 4: Track Performance and Know Your Market
As discussed in Strategy 1, records are the key to establishing the road map of where the herd has been, current status, and plans for the future. Simple record-keeping that allows for the assessment of key performance indicators such as calf weight per cow exposed, weaning weight, and returns on per cow basis are necessary for buying the right bull.

Additionally, our beef industry continues to evolve rapidly. Staying abreast of changes and developments that will impact costs of production, marketing strategies, and profitability are important. A visionary approach will assist in establishing both short and long-term goals and objectives.

In summary, consider all strategies that will assist your operation in finding the right bull. The right bull for your operation may not be the most popular, or at the top of the sale order, but through strategizing properly a bull which will fit your needs can be successfully identified and secured- thus increasing the odds for success.

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Maximizing Beef Bull Fertility and Reproduction
By T. Hamilton - Beef Cattle Specialist, OMAFRA - A major objective in a cow-calf operation is to produce one calf from each cow annually. The degree to which producers meet this goal influences their net income.

 

Introduction
A key component of efficient calf production is a high fertility level in each breeding animal in the herd. Since individual bulls service many females, a deficiency in the breeding ability of one bull has a larger impact on herd productivity than fertility problems in a single female. Using a subfertile bull may lead to longer calving intervals, a lower number of calves produced and increased costs from wintering open females. All of these results cause serious economic loss to the cow-calf producer.

Bull fertility is often measured by the percentage of cycling females exposed to the bull and impregnated during a specific time period (usually 60–90 days). Actual fertility levels are the result of a combination of genetic potential and environmental factors including nutrition, health, and cow and bull management. It is not feasible to determine true fertility before a bull is used in the herd. Nevertheless, a bull can be evaluated for breeding soundness and this information used to assess his potential fertility. A few bulls may be sterile, but most have fertility levels ranging from very high to very low.
Puberty
Puberty is defined as the age at which a bull is first able to produce an ejaculate containing 50 million sperm with a minimum of 10% motility (capable of motion). It is related to age, body weight and testes weight. Age and body weight at puberty vary across breeds (Table 1), but scrotal circumference at puberty (an indicator of testes weight) remains constant at 28–29 cm. Bulls exhibit first sexual interest about 3 weeks prior to puberty and attain mating ability about 6 weeks after puberty. Although bulls that have reached puberty can breed, reproductive capacity increases as the bull continues to mature. The reproductive development and performance of young bulls has gained attention as beef breeders attempt to accelerate improvement of economic traits in cattle and reduce costs by using younger sires.



Factors Affecting Bull Fertility
There are 5 general factors that can affect bull fertility:


structural soundness

capability of the reproductive organs

quality of semen

level of libido

plane of nutrition.

All are important and a deficiency in any category will negatively affect fertility.
Structural Soundness
General health and structural soundness are important aspects of fertility. Poor health can affect libido, mating ability, and semen production and quality. Structural soundness, including functional feet, legs and associated joints, is critical for the bull to effectively travel the breeding pasture and service females in heat. Any disease that impairs the mobility of the bull hinders reproductive performance.

A conformational problem commonly associated with poor breeding performance is extreme straightness of the rear leg (post-legged). A moderate angle in the hock joints is necessary for the bull to thrust properly after mounting. Proper angulation in the leg joints also helps to absorb the shocks produced during each step and increases the productive life-span of the bull.
Reproductive Organs
Figure 1 illustrates the various parts of the bull’s reproductive tract. Sperm is produced continuously by the testes and stored in the epididymis. The prostate gland, seminal vesicles and cowper’s glands secrete the fluid component of the semen. During mating, the penis is extruded from the sheath by the straightening of the S-shaped sigmoid flexure; sperm are transported up the vas deferens to the urethra and exit via the penis.

Deep body temperatures are too warm for proper sperm production. This is why testes are located outside the body core. As the environmental temperature changes, the testes are raised and lowered in the scrotum to maintain proper temperature for sperm production.
Abnormalities of the Reproductive Organs
Various conditions can affect the function of the reproductive tract. If the testicles cannot move because of fat pads, scar tissue or a small scrotum, proper temperature cannot be maintained and semen quality may suffer. Soft testicles indicate degeneration of tissue and poor semen quality. Very small testicles indicate unsatisfactory development of sperm-producing tissue. Severe frost-bite scabs, tumours or abscesses also indicate potential problems.

Infection and inflammation can occur in any of the reproductive organs. If the testicles become inflamed, the semen quality may be impaired long after the original condition has passed, since it takes approximately 60 days for new sperm to be produced and mature.

Common penile problems include:


spiral deviation

persistent frenulum

penile hair rings.
Spiral deviation, where the penis is twisted instead of straight, is the most common problem. Bulls with this defect produce fewer pregnancies than normal bulls. Bulls evaluated using an electroejaculator may display spiral deviations that will not occur under natural conditions.

A persistent frenulum is a heritable condition in which the tip of the penis remains attached to the sheath and cannot be extended. It can be surgically corrected.

Penile hair rings are most often seen on young bulls. A band of hair encircles the penis. If the condition remains untreated infection and scarring may result. Other conditions that can affect the penis include fractures, warts and scarring from previous injuries.





Figure 1. The reproductive tract of the bull.


Scrotal Circumference
Measuring the scrotal circumference of young bulls is an accurate, repeatable method to assess current and future sperm-producing ability. The measurement gives an estimate of the weight of the testes, which is directly related to the level of sperm production. Scrotal measurement is also positively correlated with semen volume and quality. Table 2 contains minimum recommended scrotal measurements by breed and age. Bulls with adequate scrotal development for their age have a higher probability of becoming satisfactory breeders than bulls with smaller scrotal circumferences.

Scrotal circumference is of medium to high heritability. Fertility of the male offspring can be increased by selection for this trait. The scrotal circumference of a bull is also positively related to the fertility of his daughters. Heifers from sires with larger than average scrotal circumference tend to reach puberty earlier than those from bulls with smaller scrotal circumferences. Increased scrotal circumference in sires is also favourably correlated to their daughter’s age at first breeding, pregnancy rate and days to rebreeding after calving. Due to low heritability, direct selection for female fertility traits has not been successful. The strong genetic relationship between scrotal circumference and female reproductive traits provides an alternative selection method.
Semen Quality
The criteria commonly used to evaluate semen quality include sperm morphology (structure) and motility (rate and percent of progressive forward movement). Semen volume and concentration can also be used.

Consider the following points when assessing the results of a semen test.


In the field, correlations between semen quality traits and fertility have been low to moderate.

The repeatability of semen evaluations of the same bull over time have been low.

lSemen tests results for young bulls may not be conclusive. A poor semen test on a bull less than 15 months of age is not a reliable indicator that the bull will have poor quality semen a few weeks later. Seminal qualities may improve dramatically for up to 4 months following puberty.

While a bull must produce some viable sperm in order to be fertile, semen quality is only one aspect of total fertility and must be evaluated in conjunction with all the other factors.
Libido
Libido (sex drive) is a critical component of fertility. It is independent of scrotal circumference, semen quality, body weight, growth rate or masculinity. One method of measuring libido is to measure serving capacity. This is done by exposing the bull to a group of restrained females and recording the number of mounts and services completed in a given time period. This method, however, is time consuming and requires confining a number of females. Serving capacity is not commonly evaluated in Ontario at present.

When 2 or more bulls are used at the same time, in the same pasture, social interactions affect breeding performance. Social rank is related to age and seniority in the herd. The most dominant bulls tend to complete the highest number of services. In this situation, the number of cows serviced may be related more to social dominance than libido as measured by a serving capacity test.
Nutrition
Proper nutrition is necessary for good reproductive performance. Balanced amounts of protein and energy are required for sperm production and the physical activity associated with breeding. Adequate amounts of vitamins and minerals are also important in reproduction.



During the breeding season, bulls tend to eat less feed than is required to maintain their body weight. At this time they use body fat for energy and may lose up to 68 kg (150 lb). Supplying a grain mix to bulls on pasture is not always effective. Proper pre-breeding nutrition is essential to ensure the bull has adequate reserves for a successful breeding season.

Excessive fat deposits in the scrotum may interfere with temperature regulation. The degree of body fat required to adversely affect sperm production has not been well defined. Extreme fatness has been associated with low serving capacity. On the other hand, large breed yearling bulls starting the breeding season with minimal levels of backfat may have poorer semen quality than similar bulls carrying a moderate level of backfat. The nutrient requirements needed to optimize reproductive per­formance in breeding bulls needs more research.

Cow to Bull Ratio
To produce a calf every 12 months, the cow must be bred within 80 days after calving. In order to achieve high pregnancy rates in a restricted breeding season, do not overwork the bulls. Table 3 shows the number of cows that a bull of average fertility can be expected to impregnate in a 60-day breeding season on pasture. Cow numbers may be increased by about 30% if cattle are kept in a confined area or are presented to the bull only when in heat. If cow estrous cycles are synchronized and natural mating is used, the cow:bull ratio must be reduced.



Summary
Proper selection and management of the beef bull will increase the probability of a successful breeding season. A complete assessment of potential fertility includes an evaluation of structural soundness, reproductive organs, semen quality, libido and nutritional status. Selection for increased scrotal circumference should increase inherent fertility in both male and female progeny.
Selected References
Blockey. M. A. 1978. The Influence of Serving Capacity of Bulls on Herd Fertility. Journal of Animal Science 46:589.
Coulter, G.H. et al, 1987. Testicular Development, Daily Sperm Production and Epididymal Sperm Reserves in 15-Mo-Old Angus and Hereford Bulls: Effects of Bull Strain Plus Dietary Energy. Journal of Animal Science 64:254.
Lunstra, D.D. et al, 1978. Puberty in Beef Bulls: Hormone Concentrations, Growth, Testicular Develop­ment, Sperm Production and Sexual Aggressiveness in Bulls of Different Breeds. Journal of Animal Science 46:1054.
Pruitt, R. J. and L. R. Corah, 1985. Effects of Energy Intake After Weaning on the Sexual Development of Beef Bulls. 1. Semen Characteristics and Serving Capacity. Journal of Animal Science, 61:1186.
Wenkoff, M.S. 1987. The Evaluation of Bulls for Breeding Soundness. CVMA, 1987.
This Factsheet was originally authored by Tom Hamilton, Beef Cattle Production Systems Program Lead, New Liskeard, OMAFRA and Deb Stark, Chief Veterinarian of Ontario (formerly Cattle Health Consultant), Guelph, OMAFRA.

February 2007

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Management of Yearling Bulls
By Drs. Scott P. Greiner and John B. Hall, Extension Animal Scientists, VA Tech.


Winter and spring are the primary bull buying seasons in Virginia. A diligent amount of time spent studying performance information, EPDs, pedigrees and other pertinent information is warranted as sire selection is the most important tool for making genetic progress in the herd.

Of equal importance is the care and management of the newly acquired bull. Proper management and nutrition are essential for the bull to perform satisfactorily during the breeding season. With most new herd sires in the state purchased as yearling bulls- management prior to, during, and after the first breeding season is particularly important.

Management Prior to the Breeding Season
Many newly purchased yearling bulls have recently completed a performance test, which provided a high plane of nutrition. Upon completion of this test, the energy level of the diet should gradually be reduced to prevent excessive fat deposition. The reduction in energy may be accomplished through restricting intake of high energy grain supplements, in conjunction with supplying a total diet lower in energy content (primarily forage). Young bulls should be managed to be a body condition score 6 at turn-out. This will give the bull adequate reserves of energy for use during the breeding season. Yearling bulls can be expected to lose 100 pounds or more during the course of the breeding season.

Acquiring a new yearling bull at least 60 to 90 prior to the breeding season is critical from several aspects. First, this leaves ample time for the new bull to get adjusted to the feed and environment of his new home, as well as an opportunity for several new bulls to be commingled for a period of time prior to turnout. Secondly, adequate exercise, in combination with a proper nutritional program, is essential to “harden” these bulls up prior to the breeding season. A facility for the newly acquired bull that allows for ample exercise will help create bulls that are physically fit for the breeding season. The nutrition of the bull will be dependent on body condition. Yearling bulls are still growing and developing, and should be targeted to gain 2.0 to 2.5 pounds per day from a year of age through the breeding season. Bulls weighing approximately 1200 pounds will consume 25 to 30 pounds of dry matter per day. This intake may consist of high quality pasture plus 12 lbs corn, grass legume hay plus 12 lbs corn, or 80 lbs corn silage plus 2 lbs protein supplement. Provide adequate clean water, and a complete mineral free-choice.

Prior to the breeding season, all bulls should receive breeding soundness exams (BSE) to assure fertility. All bulls that are to be used should have a BSE annually. Because a variety of factors may affect bull fertility, it may be advisable to re-test young bulls before the breeding season even if it has only been a few months since their pre-sale BSE.
Management During the Breeding Season
The breeding season should be kept to a maximum of 60 days for young bulls. This will prevent over-use of the bull, severe weight loss and reduced libido. Severe weight loss may impair future growth and development of the young bull, and reduce his lifetime usefulness. When practical, supplementing young bulls with grain during the breeding season will reduce excessive weight loss.

In single-sire situations, young bulls can normally be expected to breed a number of females approximately equal to their age in months. Using this rule of thumb, a newly purchased bull that is 18 months of age could be placed with 18 cows or heifers. Bulls used together in multiple-sire breeding pastures should be of similar age and size. Young bulls cannot compete with older bulls in the same breeding pasture. A common practice is to rotate bulls among different breeding pastures every 21 to 28 days. This practice decreases the breeding pressure on a single bull. Some producers use older bulls early in the breeding season, and then replace them with young bulls. The appropriate bull to female ratio will vary from one operation to the next based on bull age, condition, fertility, and libido, as well as size of the breeding pasture, available forage supply, length of the breeding season and number of bulls with a group of cows.

All bulls should be observed closely to monitor their breeding behavior and libido to ensure they are servicing and settling cows. Additionally, observe the cowherd to monitor their estrous cycles. Many females coming back into heat may be the result of an infertile or subfertile bull. All bulls should be monitored for injury or lameness that may compromise their breeding capability.
Management After the Breeding Season
Young bulls require a relatively high plane of nutrition following the breeding season to replenish body condition and meet demands for continued growth. Yearling bulls should be maintained in a separate lot from mature bulls, so these additional nutritional requirements can be provided. Body condition and projected mature size of the bull will determine his nutrient requirements during the 9 months following the breeding season. Bulls should be kept away from cows in an isolated facility or pasture after the breeding season. In the winter months, provide cover from extreme weather that may cause frostbite to the scrotum resulting in decreased fertility.

All herd bulls should receive breeding soundness exams (BSE) to assure fertility on an annual basis. Assess the bull battery well in advance of the breeding season, so that new herd sires can be acquired in a timely fashion.

March 2007

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Observe Bull During Breeding Season
By Clyde Lane, Jr., Professor Animal Science and published by University of Tennessee in Beef Cattle Time, Volume 25, Number 2, Spring 2007


The number of calves born is an important factor in the profitability of a beef operation. Since the bull is the major contributing factor to a large calf crop, every effort must be made to ensure that he settles as many cows as possible.

First, the bull should have a breeding soundness examination performed prior to the breeding season. If this has not been done, consider doing it now. It is important for the bull to be physically fit, have the potential to produce an ample supply of viable sperm and have the ability to deliver it at the first estrus cycle of the brood cow herd.

Next, observe the bull to be sure he is settling cows. Is the bull active and actually mating with cows? If not the problem needs to be addressed immediately. Many times a bull with an injury to the reproductive tract will follow cows but will not mate.

Do not forget that there are other reasons why bulls do not get cows settled. A bull with an eye injury, or even pinkeye, will be in so much pain that he will loose interest in the cows. Be sure the bull does not have a skeletal injury that prevents or reduces his movement. A bull with foot rot, an injured foot or a stifle injury will not have a desire to breed.

Many producers do not consider whether the bull might be overworked. Placing a bull with too many cows that cover a large area can cause him to be overworked.Sometimes, an overworked bull will simply loose the desire to mate with the remaining cows.

If a young bull is being used for the first time, observe whether he has the desire to mate. Sometimes bulls that have no desire to mate with cows are found. Also observe the young bull to see that he does not spend all his time with one female while ignoring the remaining cows.

Keep a close watch during the breeding season. Remove any bulls that are not settling cows and replace them with ones that can settle cows. This is the best way to salvage a calf crop when problems occur.

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Beef Herd Management Systems Research Results
By Tom Hamilton - Beef Program Lead - Production Systems/OMAFRA. The cow-calf industry is characterized by a unique combination of variation and tradition.

 

The cow-calf industry is characterized by a unique combination of variation and tradition. Wide variety is found in the breeds, people and scale of operations involved. It's little wonder that the sector features diversity and innovation in the organization of calving and production systems. Tradition is firmly rooted in the evolution of the beef cow enterprise from the mixed-farm, where a few dual purpose cows in the barn provided both milk and meat. With only a few head to care for, calving inside the barn made total sense from a labour efficiency standpoint. Each birth was an event, and it was easy to maintain clean pens. But barn calving and intensive management started to falter as farms became specialized and the concentration of animals increased. Calf scours became an all too common feature of calving season.

 
Figure 1. Cow-Calf pairs on pasture
Research on calving alternatives was carried out at the University of Guelph's New Liskeard Research Station. The objective was to compare animal performance, cost of production and labour efficiency of two very different management systems. The conventional group was bred to calve mid-February to mid-April, with access to naturally ventilated barns during winter, calving in special indoor, but unheated pens. The alternative group was wintered in a similar manner, but were bred to calve in June and July, when they were on pasture. To create the groups, the existing herd was split into two comparable sub-herds, with similar genetic make up and age structure. Each year, the same sires were used in both groups, ensuring that differences seen in performance of the groups would be due to management system, not genetics. Other experiments conducted with the herd over this time, such as estrus synchronization, were replicated in both groups. The groups were on a common health protocol, and the same culling criteria were applied to each.

A five year summary of results showed striking differences between the systems. Pasture born calves were much less likely to receive assistance during the calving process (Table 1). In fact, barn heifers had an assist rate which was over three times greater than their grass calved counterparts, while barn cows had an assist rate five times greater than pasture cows. This is likely due in part to the lower birth weights observed with the summer born calves, who averaged 6 lbs. lighter than the winter group. Another factor may have been that the location of the calving pens made it more likely for cows to be observed during the birthing process, although pasture cows were also checked at least twice daily.

Table 1. Calving Characteristics of Seasonal Groups
Characteristic Winter Summer Probability
Birth Weight (lbs) 1 105.6 99.5 P<.05
Calving Ease Score 2 1.4 1.1 P<.05
% Assisted Births . . .
Heifers 63 17 P<.05
Cows 18 3 P<.05
1Adjusted for age of dam, sec of calf and birth type
2Scale of 1-4, 1=unassisted, 2=easy pull, 3=hard pull, 4=surgical 

The barn group of calves also experienced a much higher rate of intervention for health related issues, such as hand feeding of colostrum and treatment with anti-diarrheal products (Table 2). Interventions incur both labour and product costs. Calf survival was the same for mature cows in both groups, but the pasture group heifers had a significantly higher weaning rate (92%) than the barn heifers (80%). In this calculation, weaning rate was defined as the number of calves weaned divided by the number of pregnant females retained from the previous season, so it included aborted calves, dead on arrivals (DOAs), neonatal deaths and any calf losses from birth to weaning.

Table 2. Health and Management Characteristics of Seasonal Groups
Item Winter Summer Probability
Intervention Rate (%) 33 14 P<.05
Treatment per calf born 2.8 0.6 P<.05
Weaning Rate1 (%) . . .
1st Calf Heifers 80 92.2 P<.05
Cows 96.3 92.7 NS
1Weaning rate = # cows weaning a calf / # of pregnant cows retaining X 100


 
Figure 2. Calves born on pasture are healthier
It cost more to calve cows inside (Table 3). About 30% more bedding was required annually for the barn calving group, due to their requirement for calving and post maternity pens. In addition, more labour was expended in managing the indoor calving system, and the average cost of treatments per calf was much higher for the indoor group, relative to the pasture group.

The cost of raising cattle was greater for the conventional group compared with the pasture calvers (Table 3). It took about $47 more per cow with the winter calving system compared with the summer system. When costs were deducted from revenues within each system, the summer pasturing calving group was a clear winner. Net margin for the summer group was $113 per cow exposed to breeding, which was 45% higher than the $78 per cow realized for the traditional group. So it looks like the summer system was a clear winner in terms of profitability.

The above research results were based on a comparison of herds of the same size, but they may be also extrapolated to the farm level based on an analysis of the factors which limit herd size. Several issues have been identified as limiting herd size on farms, and thus overall profitability of the cow-calf enterprise. One is focused around calving time. With intensively managed cows, night time calving checks and the number of calves which need birthing assistance and health treatments can be limiting. This is the most stressful time of the year in beef cow herds, and the hours of labour and degree of stress increases with the number of pregnant cows. Another potentially limiting factor is the value of capital investment in the calving facilities required for winter-early spring calving. If herd numbers are increased without concurrent facility expansion, the chances of a devastating scours outbreak increases.

Table 3: Some Variable Costs Per Cow Retained, by Seasonal Groups ($) 
Item Winter Summer
Calving Season Labour1 4.21 1.28
Pasture 68  74
Stored Feed 294 293
Bedding ($/cow) 48 37
Facilities (depreciation) 67 40
Total 522.21 475.28
1Labour for pen or pasture checks, calving pen maintenance, calf processing and calf treatment

Based on these research results, theoretical calculations predicted that for a given amount of labour, 25% more cows could be kept with a pasture calving system compared with barn calving. More cows with means more total profit is generated per farming enterprise. Based on these projections, net enterprise margin would increase by about 80% if herd numbers could be expanded from 80 hd to 100 hd, when switching from barn calving to pasture calving. Expanding or establishing very large cow herds (200+ cows) is a daunting challenge with a traditional management system based on confinement calving in late winter-early spring. A move to extensive management with pasture calving during late spring and summer could be a viable and profitable option.

Table 4. Net Margin Per Cow Per Exposed, by Management Group ($) 
Item Winter Summer
Revenue 611 592
Costs 533  479
Net Margin 78  113


November 2007

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Selecting bulls for structural soundness in beef cattle
By John Bertram et al , Department of Primary Industries and Fisheries.


Introduction
The structural soundness of bulls influence the ability of a bull to deliver his genetics to the point of fertilisation (in the cow) for as long as the cattle breeder chooses to use the bull in the herd. Structural soundness embraces a range of traits of the more rigid skeletal structure as well as the softer tissues critical to bull function. We will discuss these under the general headings of Feet and legs, Head and eyes, Sheath and penis.


Assessment of bulls
‘Eyeball’, subjective, or visual assessment selection of bulls, is still the most common procedure for many bull buyers. However, this assessment is often done without any clear regard to many functionally important reproductive traits. It is not uncommon for bulls selected with subjective appraisal to have some reproductive and structural abnormalities that are not clearly visible when presented for sale, and may contribute to sub-optimal herd fertility levels.

A bull breeding soundness examination is a systematic examination of a bull conducted by a veterinarian and provides opportunity for comment on the animal’s structural soundness. This thorough physical examination can be quick and easy to carry out, and should be a routine procedure pre-sale. A similar procedure can be conducted on property prior to joining and provide evidence for culling unsound bulls.

Functional anatomy of a bull
A bull should be capable of walking long distances, especially in the extensive conditions of north Australia and be able to maintain his body condition. He should have the ability to detect females on heat, and be capable of serving females as they display oestrus. Soundness of limb and skeletal structure contribute to the bull’s longevity and functional effectiveness. Important points of functional anatomy include:
conformation (particularly hind limb) of the legs and hooves
head and eyes
pelvic size
scrotal circumference and testicular tone
sheath size and shape
Conformation of the legs and hooves
Hind leg conformation

Examination of hind leg conformation is an essential phase in evaluating bulls. Sound hind legs are vital to the mating ability of bulls as during mating most of the bull’s weight is supported by the hind legs. The leg should be free of excessive swelling at any of the joints with joint flexure smooth and free of locking in any position. A bull with hind leg defects may suffer pain on moving or mounting which may interfere with its desire to mate. In an ageing bull with faulty conformation, defects become more apparent and may tend to increasing interference with serving ability.

Straight hind legs or ‘post legs’ in the bull predispose the bull to swollen hocks and arthritis in the hip and stifle joints. Sickle hock bulls tend to be clumsy, particularly at service and when dismounting. Each of these conditions can adversely affect a bull’s serving capacity in the longer term. Conversely, a bull will ‘break down’ earlier in life if it has straight legs or sickle hocks as shown in Figure 1.


Figure 1. Hind limb conformation (a) normal, (b) bow legged, (c) cow hocked.



The hooves

Both hooves should be of suitable size to weight bear with the claws of approximately equal size and shape. While defects of the hooves are often associated with poor limb conformation, they may be associated with overfeeding of young bulls, mineral deficiencies, soft soil surface or lack of exercise and confinement in a restricted area.

Figure 2. Pastern angle of front and hind legs and associated claws: (a) correct structure (b) weak in the pastern (c) too straight.




Worn toes are often an indication of the hoof being dragged, which would suggest straight hind legs. Common problems in the hooves include:

both hooves not symmetrical in size and shape (Figure 2a)
short hooves, worn at the toe (Figure 2c), often associated with straight hind legs
long, narrow hooves with shallow heels, often associated with weak hocks and pasterns and sometimes form scissor hooves.

The walk

The gait should be well coordinated and smooth with the rear hooves placed in the imprint of the front feet. As a bull moves freely forward, each leg should pass through a plane parallel to the mid-line of the body and not swing in or out as it is carried forward.

Overstepping or understepping may be linked to serving ability of the bulls. Bulls that understep often have straight hind legs and have increased mating problems.


Head and eyes
The upper and lower jaws should be of a similar length (not undershot or overshot) and free of abscesses or swellings. Viruses, animal age, genetic background, UV light and solar activity have been implicated in the development of eye lesions. Bos taurus type cattle have a relatively higher proportion of squamous cell tumours in unpigmented or partially pigmented regions around the eyes. ‘Pop eyes’ protrude from the profile of the head and predispose the bull to cancer eye or injury to the eye. From practical observations, eye cover or hooding with well-set eyes would appear to not only provide greater physical protection, but also ensure decreased glare, ultra violet light and reduced fly related problems.
Pelvic opening
A small pelvic opening, which is heritable can predispose the herd to subsequent calving difficulty and may therefore be considered as an important selection trait.


Sheath size and shape
Large pendulous sheaths are not uncommon in Bos indicus breeds and will predispose the bull to prolapse and preputial damage. Some bulls have a very thick residue of the umbilicus (navel) which is often associated with a large inverted fold of skin referred to as the ‘rosette’. Both of these conditions appear to limit the bulls’ ability to sire calves.
Scrotal circumference and testicular tone
Scrotal circumference is a measure of the daily and total sperm production of a bull. In Bos taurus bulls scrotal circumference should measure 32cm at 2 years of age, whilst Bos indicus bulls in harsh nutritional conditions should measure 28cm at the same age. Testicular tone is an approximate indicator of testicular function. The percentage normal spermatozoa in an ejaculate produced by the testicles is a preferable indicator of the bulls ability to sire calves.

June 2005

© The State of Queensland (Department of Primary Industries and Fisheries) 1995 - 2006.

Queensland Government

[mikey]

Don’t Forget About the Bulls
By by Bethany Lovaas, DVM. University of Minnesota Beef Team, North Central Research and Outreach Center.

 
As the breeding season approaches, generally everyone is thinking about getting cows and heifers in shape for the breeding season. A nice, tight breeding season results in a nice tight calving season, which generally is the most economical for producers. However, the cow is only half of the equation. Don’t forget about the bulls!!

Bull Breeding Soundness Exams
One of the most important, and often under utilized tools available to beef producers is the bull breeding soundness exam (BSE). A BSE will allow the technician/veterinarian to assess the fertility of a bull based on scrotal circumference, sperm motility, and sperm morphology. The minimum benchmarks that a bull must reach for each of these parameters are:

Sperm motility: 30%

Normal sperm morphology: 70%

Scrotal circumference: 30cm (15 mo. of age) to 34 cm (24 mo. of age)
A breeding soundness exam also allows for the opportunity for a thorough examination of most of the bull’s reproductive tract, and can identify causes of infertility (corkscrew penis, persistent frenulum, etc.) that may have gone unnoticed until late in the breeding season.
Feet and legs
When selecting herd bulls, emphasis is placed on growth performance, EPD’s, and soundness. These are all good criteria, and no one should try to use a lame or unsound bull for breeding. However, there is nothing wrong with putting a bull on the table for a good foot trim, if he needs it, a month before the start of the breeding season. A bull has to put on a lot of miles, and mount a lot of cows in any given breeding season, and even sound bulls can develop foot problems. If he’s going to hit the ground running, he should have the best set of wheels he can get.
Vaccination/deworming
If bulls are housed separately from the cows for most of the year, they are often forgotten and do not receive the same herd health protocol. The herd bulls should be on the same vaccination/deworming schedule as the cows are. Since vaccination schedules vary as much as production systems do, there is no “correct” schedule that everyone should stick with. So, if in doubt, vaccinate and/or deworm your bulls about 2 weeks before they go out to pasture. This will allow for enough time for the vaccine and dewormer to take effect before the bull is exposed to the cows. It also is a good idea to deworm the cowherd before they go out onto the pasture. This will clean out the cows’ systems and limit the parasite burden on the pasture during the spring and early summer.
Body condition
When a bull is out on pasture breeding many cows, his mind is only on one thing, and it’s not feed. In the peak of the breeding season, some bulls will breed 6-8 cows a day, and will hardly eat. Therefore, it is very important to make sure a bull goes out on pasture in good condition, so that he has plenty to lose by the time the breeding season is over. Bulls should be in a similar body condition score to replacements heifers, ideally, from 5 to 6.5.
Bull: Cow Ratio
There is a lot of variation in producer opinions about how many cows a bull can service during the breeding season. Instead of trying to memorize numbers, try this little rule of thumb: one bull can service as many cows as he is months old, up to fifty months.

For example:

A 15-month-old bull can service 15 cows

A 24-month-old bull can service 24 cows

A 50-month-old bull can service 50 cows
After 50 cows, you are starting to really push the limits of what even an older, more experienced bull can accomplish in a 60 day breeding season. If you have much more than 50 cows/bull, and are still attempting to stick to a 60-day breeding season, you may want to add to your bull arsenal, or explore other options to maximize your present bull power.
Young bulls vs. Older bulls
If a producer has more than one bull, often one bull is older than the other. This helps minimize fighting between the bulls, but the older bull is the smarter, dominant bull, and will get more cows bred. One technique to get around this problem is by rotating your bulls through the cowherd. Start by putting the young bull out with the cows by himself for a couple weeks, then switch the bulls, and send the older bull out with the cows for a couple weeks. This will ensure that the cows are being exposed to the young bull, and will also help him maintain his weight more effectively.
Bull rotation also can be a very effective means of stretching your bull power if you need to. By giving each bull 2 weeks on and 2 weeks off, you are giving each a much needed rest, and an opportunity to go out fairly fresh multiple times during the breeding season. This system does create questions about which bull sired which calves. So if you register your calves or report data on your herd, this may not be a good option for you.
Fertility Associated Antigen
Some bulls are inherently more fertile than others. This is due in part to a protein called Fertility Associated Antigen (FAA). The FAA protein is found on the sperm cells of some bulls and results in a higher percentage of sperm capacitation, and therefore a higher rate of fertilization. Studies show that bulls that are FAA positive are about 17% more fertile, and get more cows bred in a 60 day breeding season. There currently is a chute-side test available from ReproTec, Inc. Tucson, AZ that can test for FAA. It takes about 20 minutes per bull and can easily be incorporated into the routine bull breeding soundness exam.

Whether they are used as the primary breeding source, or are used for clean up after an AI program, healthy herd bulls are a big part of a successful breeding program. By ensuring that your bulls are in tip-top condition before turnout, you can make great strides in the efficiency and economy of your cowherd.

May 2007