chapter 20. beef cattle breeding

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Chapter 20. Beef Cattle Breeding By John Evans, David Buchanan, and Sally Northcutt

Objectives • Identify key factors for genetic improvement. • Review the application of different selection

methods. • Summarize information available through the

Beef Improvement Federation. • Examine the basic concepts of genetic pre-

diction. • Differentiate and summarize mating systems.

Beef cattle producers have a wide array of methods for exploiting the genetic diversity available in beef cattle. Many breed associations have been very aggressive in adopting new methodologies for genetic improvement. There are many excellent breeds from which to choose. This diversity in methodology is important because the environments in which beef cattle are produced are extremely diverse. The beef cattle industry has been blessed with a dynamic organization that promotes beef cattle improvement and develops new improvement procedures. This organization is the Beef Improvement Federation (BIF). BIF began in 1968 as a forum for producers, test station managers, breed associations, extension specialists, and scientists to discuss beef cattle improvement. Many procedures have been recommended and put into practice by beef producers. There is still much work to do.

HERITABILITY AND SELECTION Heritability

Traits measured in beef cattle populations are the sum of the genetic and environmental factors which have an effect. Heritability indicates the proportion of the differences between individuals that is genetic. Heritabilty is not constant. It varies from herd to herd and can vary within a herd if the management or the system of mating changes. Much research has been directed toward looking at heritability for various traits in livestock. Averages of the estimates from many studies for beef cattle are shown in Table 20.1. As a rule of thumb, most reproductive traits tend to have low heritability (<0.20), growth traits tend to

have moderate heritability (0.20 to 0.40), and carcass traits tend to have fairly high heritability (>0.40).

Probably, the most important practical use of heritability is that it indicates how easy it is to make genetic improvement through selection. As can be seen from the published estimates of heritability (Table 20.1), it is much easier to show selection progress for growth and carcass traits than reproductive traits.

This has led some to decide that reproductive traits should not be included in a selection program; however, this idea overlooks the fact that reproduction is the most economically important factor in the efficiency of most beef enterprises. The importance of traits associated with reproduction makes up for the low heritability so that reproduction should be considered for most selection programs. More recently, the research and development of traits for heifer pregnancy and stayability (the probability a cow reaches a minimum of 6 years of age) indicate heritability estimates are equivalent or higher than milk. Table 20.1 – Heritability estimates for beef cattle.

Trait h2

Birth weight 0.35 Weaning weight 0.30 Weaning score 0.25 Feedlot gain 0.45 Carcass grade 0.40 Fat thickness 0.33 Rib eye area 0.58 Marbling 0.42 Retail product percent 0.30 Calving interval 0.08 Conception rate 0.05 Gestation length 0.35 Milk 0.20 Pasture gain 0.30 Yearling weight 0.40 Feed efficiency 0.38 Dressing percent 0.38 Tenderness 0.55 Cancer eye 0.30

Source: Cundiff, L.V. and K.E. Gregory; Lasley, J.F.; Taylor, R.E.

Heritability also indicates the proportion of the superiority in an individual or in a group of individuals that can be passed on to the next generation. This property is used to estimate breeding value. Breeding value is the value of an individual as a parent. The “true” breeding value of an individual is never known. It can be estimated from performance of the individual and its relatives. Common types of relative information are progeny, sires, and parents. Distant relatives contribute little to the estimate of breeding value.

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Genetic Correlation Genetic correlation refers to the situation where

two traits are controlled by the same or many of the same genes. Knowledge of the magnitude of the genetic correlation between various traits is useful in a selection program. For example, individual feed efficiency is a trait that can be difficult and expensive to measure. Individual rate of gain is a relatively easy and inexpensive trait to measure. A favorable genetic correlation exists between rate of gain and feed efficiency. Selection can be directed toward rate of gain, which is easily measured. If this rate of gain is improved through selection, some improvement is expected in feed efficiency due to the favorable genetic relationship between the two traits. Genetic correlations are not always favorable. For example, selection to increase yearling weight has an adverse effect on calving difficulty.

Response to Selection Selection is the practice of allowing certain

individuals a greater opportunity to reproduce than others. It is the only means of directing genetic improvement in closed populations. Selection may be practiced for one trait or for a complex of traits. The results of selection are predictable in magnitude and direction.

Progress resulting from selection is called response. It is the genetic change that occurs as a result of selection. Response is a function of the heritability and the selection differential. Selection differential is defined as the difference between the mean performance of the individuals selected to be parents and the average of the entire herd. The primary opportunity to apply selection pressure is through sire selection. The bull has a direct impact on progeny performance and in many cases his daughters become replacement females in the herd. Combining these two influences of the bull, a high percentage of all genetic improvement within a herd is due to sire selection.

Generation Interval The length of time to turn over a generation is

highly variable between herds. It is a function of the reproductive rate of the animals and how long a producer is willing to keep individuals in the herd. Generation interval is a term used to express the length of time it takes to replace the members of one generation in a herd. The generation interval in many beef cattle herds will fall in the range of 3 to 4 years for males and 4.5 to 6 years for females.

APPLICATIONS OF SELECTION Individual breeders can, and should, obtain and

use performance information on as many of the animals in their herd as possible. With the advent of home computers and data management software, this information can be very easy to summarize and use. Even without sophisticated equipment, many economically important traits can be measured and used in selection programs with only minimum labor. Many producers can take advantage of breed association or extension programs, which obtain information of various types and supply summaries to their clientele. Additionally, producers can also take advantage of software packages specifically designed for management of beef cattle data. OSU Current Report 3279, “Cow-Calf Production Record Software,” outlines the characteristics of several popular beef cattle software packages. Many of these programs also interface with financial management programs.

One of the most exciting programs for animal improvement is National Cattle Evaluation. Many beef cattle breed associations have developed Genetic Evaluation programs. Bulls from different herds can be compared easily since artificial insemination is widely used in beef cattle. Each organization publishes a book listing the bulls in the evaluation with pertinent breeding value information on a variety of traits. Currently, several breed associations are using the internet to disseminate information to their members and commercial clients. For example, producers are able to electronically search a breed’s genetic evaluation database and access current information and updates about their breed.

Selection should be exercised vigorously in all seedstock herds. Commercial herds need to have programs for culling of inferior animals and for selection of young replacements, but the major improvement should be taking place in seedstock herds that supply breeding stock for commercial herds. A commercial producer is dependent upon their suppliers of breeding stock for most of the improvement that will occur. Selection intensity is a precious resource that should be carefully used without wasted effort on traits that do not contribute to efficiency of production. The discussion that follows will outline examples of the various programs that are available for improvement of beef cattle.


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On-Farm Testing All producers of livestock should have some

program of identifying those animals with superior performance so that only the best will be allowed the opportunity to reproduce. Such a program may be very complex with many traits, measures, and sophisticated record-keeping systems or very simple with only a few traits evaluated and animals classified into general groups instead of specific records being kept. The complexity of the system will depend upon several factors, including the need for making improvement as opposed to simply eliminating inferior animals. A commercial producer who obtains breeding stock from other sources will not need a very complex system since selection will be primarily culling of animals with inferior performance. A seedstock producer who practices mostly within-herd selection will need to have very complete records so that the increase in genetic merit will be as rapid as possible.

It is very important to maintain uniform management of the animals to be compared. It is also important to evaluate as many of the animals in a herd as possible. Uniform management is important so that heritability is maximized. Accuracy of measurement is also critical. Scales and other measuring devices should be appropriate for the animals being tested. It is impossible to make fair comparisons of individuals if all are not managed alike. Most, if not all, of the individuals in a herd should be tested so that an accurate assessment of the merits of the herd can be obtained. It is permissible to make intermediate removals of obviously inferior animals but genetic improvement will be maximized if comparisons are made with as large a proportion of the herd as is possible. The importance of whole-herd testing will have to be weighed against the practical problems of testing large numbers of individuals.

The performance of an individual should be considered relative to the performance of its contemporaries. An above average individual in one herd would likely be above average in many other herds even if the average performance in the herds is different. A large part of the differences between herds is due to the management differences. Use of a ratio will help a manager or a prospective buyer understand the performance of the individual relative to others managed similarly. This ratio is constructed as follows:

Individual record Ratio = Avg. of animals in contemporary grp. x 100

An average animal will have a ratio of 100 while above average animals have ratios above 100 and below average animals have ratios below 100. Ratios are useful tools within herd; however, more advanced tools, such as Expected Progeny Differences (EPD), are superior with greater accuracy. The reliability of the selection decision is greater using EPD.

Any testing program starts with identifying the animals and recording the date of birth. There are many systems for ear tags, notches, or tattoos that are used to identify animals at birth. The date of birth is important since adjustments will need to be made for age differences even if other measurements are not obtained. The conditions of birth (and birth weights if taken) should also be recorded as soon as possible after birth. This includes any unusual aspects concerning the birth (such as degree of calving difficulty). It is useful to weigh the animal at weaning. Various weights and other measurements should be obtained on the animal as it matures.

There are organizations that have on-farm testing programs for their clientele. Most major breed associations, state or national extension groups, as well as some private companies, provide record keeping, and genetic evaluation systems for different groups of producers. Even with the advent of home computers, it is recommended that all seedstock producers participate in such a program. For most breeds, centralized performance records provide the basis for national evaluation programs so that individuals can be fairly compared between farms and ranches.

CENTRAL TEST STATIONS There are several central bull test stations in the

United States where bulls from different herds are evaluated for postweaning performance under uniform conditions. Test stations were developed as a demonstration of performance testing so that producers could use similar procedures for on-farm testing programs. They also help

• Locate and recognize superior breeding bulls. • Evaluate breeding stock belonging to individual

producers. • Demonstrate effective testing of postweaning

performance.


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• Provide a source of performance-tested bulls for both commercial and purebred breeders.

• Assist in the improvement of economically important traits for beef cattle.

• Provide access to advanced technology, such as ultrasound (ribeye area, backfat thickness, and intramuscular fat percentage).

• Provide an educational forum for producers to receive updates on current issues related to the beef cattle industry.

Central test stations should be considered as a supplement to good on-farm programs, not as a replacement for them.

NATIONAL CATTLE EVALUATION The goal of National Cattle Evaluation is to

compare beef cattle (males and females, parent, and non-parent) from different herds within breed for genetic merit. Several beef breed associations conduct National Cattle Evaluation Programs. Breed associations use progeny records, individual performance records, and records on all possible relatives in the programs. National Cattle Evaluation procedures depend upon heavy use of AI so that comparisons can be made between herds.

All cattle evaluation programs calculate breeding values for various traits for the individuals in the program. Comparisons between herds are possible because many bulls are used in several herds. These “Reference Sires” create ties between herds so that indirect comparisons can be made between bulls that do not have offspring in the same herd. An example follows in Table 20.2. Table 20.2 – Use of a reference sire to compare between herds.

Herd 1 Herd 2 Herd 3

Reference sire Bull A Bull A Bull A Avg. calf weight 450 500 550 Home sire Bull 1 Bull 2 Bull 3 Avg. calf weight 460 480 500

These three herds all have calves sired by Bull A. Therefore, he is the Reference Sire. Each herd also has calves sired by one bull that is unique to that herd. Comparisons of these Home Sires are made through the Reference Sire. In Herd 1 the calves of Bull 1 are 10 lb heavier than those of Bull A. We conclude from this that Bull 1 is superior to the Reference Sire. In Herd 2, the calves of Bull 2 are 20 lb lighter that those of the Reference Sire. Therefore, Bull 2 must be somewhat inferior to those

of the Reference Sire. In Herd 3, the calves of bull 3 are more inferior to those of the reference sire. From this we conclude that the three Home Sires rank 1 : 2 : 3. This is despite the fact that the actual weaning weights of the three bulls rank in the opposite order. It is assumed that there are large differences in management for the three herds since the calves by the Reference Sire differed so widely between herds. It is also assumed that the bulls were mated to randomly chosen groups of females in each herd and that similar numbers of calves were produced by each bull in each herd.

The evaluation of breeding value in beef cattle is a rather complex problem in statistical analysis. However, at its base these between and within-herd comparisons are needed so that cattle can be compared nationally.

PERFORMANCE PROGRAMS Adjustment Factors

For selection to be effective, a producer needs to do everything possible to increase heritability. Raw data for some sources of environmental variation can be corrected. These sources include age of dam, sex, and age of the animal when the trait was measured. For example, any herd has females of varying ages. Generally, enough is known about differences due to age of dam that the records of individuals with young dams can be adjusted so they can be fairly compared with individuals with mature dams. The two main categories of beef cattle adjustment factors are (1) adjustment to common age, (2) adjustment to common age of dam.

The beef cattle adjustment factors and formulas are from the Guidelines for Uniform Beef Improvement Programs which are published by the Beef Improvement Federation (http://www.Beefimp rovement.org). Adjustment factors and formulas have been developed from large sets of data that were obtained under a wide variety of environmental conditions. Also, many breed associations have developed specific adjustment factors for their breed. Any purebred producer should use the adjustment factors developed for the breed of interest instead of the general adjustment factors.

Beef Cattle Performance Testing procedures are found in Guidelines for Uniform Beef Improvement Programs, 8th Edition. The guidelines recommend procedures for on-farm and central test performance programs and describe the techniques for National Cattle Evaluation.

http://www.Beefimprovement.org


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The following discussion is paraphrased from the current BIF Guidelines with additional material from the 3rd Edition Beef Cattle Manual.

WHOLE HERD REPORTING The concept of Whole Herd Reporting (WHR)

has been around for several years. In comparison to a traditional breed association model, many associations use a system focused on registration of the calf and ignore information on animals that did not wean a calf or performed below expectations. A WHR system requires collection of production data on all animals within a herd including animals without a calf.

The WHR system requires information to be collected on those animals in the breeding herd, which is labeled the herd inventory. Using this approach, producers are submitting data to their respective breed associations as a function of the breeding animals and not the calf. A producer is not obligated to register every calf, but WHR requires submission of required data on each calf.

The BIF guidelines have a complete description of WHR; here is a brief overview of the recommendations.

Heifers Exposure Inventory A WHR system provides the necessary data to

develop many new reproductive traits, such as heifer pregnancy and stayability. It is well documented that reproductive traits are economically important for a beef cattle enterprise. Therefore, a yearling heifer exposure inventory is needed for collection of reproductive information on future replacement heifers. This information includes breeding dates, exposure status, management codes, mating practices, and disposal codes.

Breeding Herd Inventory A producer uses a breeding herd inventory to

designate those animals in their herd. Twice a year, the breed association sends a breeding herd inventory to producers for either spring or fall calving herds. The producers are required to update their inventories for animals culled from the herd or animals added to the herd.

Producers are required to follow an annual schedule for submitting performance information to the breed association. The structure of the fees should be designed for producers to report complete and unbiased data. The value of a WHR system is focused on the collection of completely reported information. The fees structure should require submission of all production and performance data, encourage accurate updates of

inventories, and encourage the registration and transfer of seedstock animals going into a commercial production environment.

Female Production Data Traits associated with reproduction or fertility

are the most economically important traits in beef cattle. Breeders are urged to record reproductive performance in both the female and male animals.

Breeders can use specific measures of reproductive performance in the female to monitor overall reproductive performance, identify genetic and environmental areas in which to concentrate improvement efforts, and to make routine selection and culling decisions. Typical data to record on the female :

• Breeding dates – Record actual date of artificial insemination or observed natural service or record beginning and ending natural service exposure dates.

• Pregnancy status – Between 50 and 150 days following breeding, pregnancy status should be determined using rectal palpation or ultrasound. Culling of open cows after this determination is an excellent way to improve herd efficiency.

• Calving date – Each calf’s birth date should be recorded carefully.

• Calving difficulty/ease (dystocia) score – The following scoring system is recommended: 1 – No difficulty, no assistance. 2 – Minor difficulty, some assistance. 3 – Major difficulty, usually mechanical assist-

ance. 4 – Caesarean section or other surgery. 5 – Abnormal presentation. (Do not include

when herd average is calculated, but report to your respective breed association.)

Dystocia influences herd economics in a variety of ways. Calf survival rate is decreased when calving difficulty is severe. Labor and veterinary costs are increased if there is substantial calving difficulty. In addition, it has been shown that rebreeding is less efficient for cows that experienced calving difficulty.

Several breed associations include calving ease EPD (direct and maternal) in their genetic evaluations. Calving ease is the economically relevant trait. Therefore, it is important to submit calving information. In addition, producers should continue to report corresponding birth weight information, which can be used as an information source for calving ease EPD.


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Table 20.3 – Codes recommended for record-keeping systems. Disposal codes: Birth to weaning 1 – Stillborn/full term 2 – Died at birth - defect 3 – Died at birth - other 4 – Born alive, died before weaning - disease 5 – Born alive, died before weaning – other Disposal codes: Weaning to two years of age 10 – Died after weaning – disease 11 – Died after weaning – other 12 – Culled – feet and legs 13 – Culled – performance 14 – Culled – temperament 15 – Sold exposed – open 16 – Sold exposed – pregnant Disposal codes: Mature cows and bulls 30 – Sold – certificate not transferred (if seedstock) 31 – Culled – teat and udder 32 – Culled – feet and legs 33 – Culled – reproduction 34 – Culled – productivity/progeny performance 35 – Culled – temperament 36 – Culled – age 37 – Died – age 38 – Alive but not active in herd inventory (bulls only) Reason codes: Reason codes should be utilized to document why a cow did not raise a natural calf 50 – Open – missed calving opportunity 51 – ET program – donor dam 52 – ET program – recipient dam 53 – Moved to next calving season 54 – Aborted / premature

• Gestation length – Calculate the number of days between known breeding date and subsequent calving date. Cows with longer gestation periods have a shorter period of time after calving to get ready for rebreeding.

• Calving interval – Calculate yearling calving interval as the number of days between the last and second-to-last calving. Cows with consistently long yearly calving interval may eventually fail to rebreed under fixed breeding season management. Using lifetime calving interval, a producer can evaluate overall herd reproductive performance.

• Cow weight – Record mature cow weight at least once a year. A practical time to record cow weights is at weaning; however, additional weights taken at alternative times may prove to be informative. A producer can use information on cow weight information and other indicator traits (i.e., Body Condition) to monitor individual or whole herd nutrient requirements.

• Cow body condition score – A producer scores the trait using a subjective visual evaluation system. The degree of condition indicates the animal’s nutrient requirements. The scores reflect different degrees of fatness ranging from

1– severely emaciated to 9– severely obese. A 75 to 80 lb change in body weight (assumes an average weight of 1,100 lb) is associated with a one body condition score difference.

Male Reproduction Data It is important to evaluate bulls for reproductive

soundness. The most important concept is to make sure that no bull is used that has fertility problems. It is difficult to differentiate between degrees of acceptable male fertility. However, with proper procedures, it is possible to identify many of the bulls that will be problem breeders. The Society for Theriogenology establishes a standard set of guidelines and recommendations for breeding soundness exams. A qualified and trained veterinarian or professional should conduct the breeding soundness examination. The following procedures are recommended: • History and physical examination – A competent

evaluator should examine each bull for any injury or abnormality. These defects include vision problems, foot and leg injuries, and abnormalities that might prevent the mating process. This evaluation should include an evaluation of the scrotum and testes, rectal palpation of internal accessory glands, and examination of the extended penis and prepuce.

• Scrotal circumference – The scrotal circum-ference is an indicator of the bull’s ability to produce sperm and is related to age at puberty in the bull itself, as well as the bull’s daughters. It is measured at the widest part of the scrotum in millimeters or centimeters. A yearling bull should measure at least 30 cm to be considered acceptable (Table 20.4). Table 20.4 – Minimum recommended scrotal circumference.

Age (mo.) SC (cm)

< 15 30 >15 and < 18 31 > 18 and < 21 32 >21 and < 24 33

> 24 34

Source: Society for Theriogenology.

• Semen evaluation – A trained technician should collect semen samples using electro-ejaculation, an artificial vagina, or rectal massage. The technician should evaluate the percent motility and morphology (Table 20.5). Morphology includes primary and secondary abnormalities,


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Table 20.5 – Motility ratings. Mass Activity (Gross) Rating Individual

Rapid swirling Very good > 70% Slower swirling Good 50-69% Generalized oscillation Fair 30-49% Sporadic oscillation Poor <30%

Source: Society for Theriogenology.

as well as the presence of other cells (i.e., white blood cells). If abnormal cellular material is present in the ejaculate, the technician should include this information in the report. Minimum recommended motility is 30% or Fair.

• Classification of bulls – A bull is categorized into one of three classes based on the results of their breeding soundness exam. ο Satisfactory – meets or surpasses the

minimum requirements for scrotal circumference, semen evaluation, and physical exam.

ο Unsatisfactory – fails to meet the minimum requirements for scrotal circumference, semen evaluation, and physical exam.

ο Deferred – does not fit into either the satisfactory or unsatisfactory categories. This bull requires additional maturity or a recovery period to address temporary problems.

• Breeding soundness report – The following items should be included in a complete breeding soundness exam: ο Contact information (name, address, and

location) ο Date of current and future examinations ο Animal identification (i.e., tattoo, eartag),

breed, and age ο Animal history, weight, condition, and

previous reproductive exam results ο Results of physical exam, scrotal

circumference measurements, semen motility estimate, and semen morphology

ο Status of exam (Satisfactory, Unsatisfactory, or Deferred)

ο Signature and address of veterinarian conducting the examination

Sire and Herd Reproduction Overall herd reproduction efficiency can be

evaluated in a variety of ways. The following procedures are recommended:

• Number of cows exposed – The number of cows exposed for either artificial or natural service in the present year’s breeding season.

• Percent palpated pregnant – This is a measure of the success of the breeding season. It is calculated as follow:

No. of cows diagnosed pregnant % palpated pregnant = No. of cows exposed at breeding

x 100

• Live calving percent – this is a measure of the success of the cumulative results of the breeding and calving seasons. It is calculated as follows:

No. of live calves Live calving % = (No. of cows exposed – No. of cows sold or died + No. of cows

purchased)

x 100

• Weaning percent – This measure is also frequently called “percent calf crop weaned.” It is recognized as the most descriptive single measure of the reproduction efficiency. It is calculated as follows:

No. of calves weaned Weaning % = (No. of cows exposed – No. of cows sold or died + No. of pregnant cows

purchased)

x 100

Evaluation of Growth Rate and Efficiency of Gain

Growth rate and efficiency of gain for beef cattle are of primary economic importance to the beef industry. Growth rate has a direct effect on net return and is positively correlated with efficiency of gain, weight, and value of retail product. Efficiency of gain has a direct effect on cost of production and net return. However, realized heritability for measures of preweaning and postweaning growth depends on how they are handled with respect to sex of animal and age of dam. The following procedures are recommended:

• Birth weight – Calf birth weight is a useful indicator of calving difficulty. Birth weights should be recorded on all calves, alive and dead. They should be obtained within 24 hours of birth. Selection of breeding animals for smaller birth weight appears to be an effective criterion for improving direct calving ease. Both sex of calf and age of the cow influence birth weight. Weight of females can be adjusted to a male


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basis by multiplying their birth weight by 1.07 (see 1996 BIF Guidelines). Age of dam adjustment factors were introduced in the section on adjustment factors. Birth weight should be expressed as a ratio to the average of the birth weights of contemporary calves. The following formula is recommended:

Individual adj. birth weight Birth weight ratio = Average adj. birth weight

of the group

x 100

Adjusted birth weight is calculated by adding the additive age of dam adjustment factor to the actual birth weight (Table 20.6). However, there are breed differences and the breed association factors should be used whenever possible.

Adj. Birth weight = Birth weight + age of dam adj. factor

Table 20.6 – BIF standard adjustment factors for birth weighta.

Age of dam Adjustment factor

2 + 8 3 + 5 4 + 2

5-10 0 >11 + 3

a BIF standard birth weights are 75 lb for males and 70 lb for females.

• Weaning weight – Calf weaning weight helps evaluate differences in mothering ability of cows and to measure differences in growth potential of calves. It is recommended that weaning weight be standardized to 205 days and a mature dam equivalent. Weaning weight should be obtained when the group of calves average age is close to 205 days and the age range to calculate adjusted 205 is 160 to 250 days.

(Weaning wt. – Birth wt.) 205-day weight = Age at weaning x 205 + Birth wt.

The first part of this formula is a calculation of average daily gain from birth to weaning using the actual birth and weaning weights. This is multiplied times 205 to give the total expected gain from birth to 205 days. The actual birth weight is then added back on to get the 205-day weight. After the 205-day weight is calculated, it is adjusted for age of dam using the age of dam adjustment factors (Table 20.7).

Adjusted 205-day weight = 205-day weight + adjustment factor

Table 20.7 – Standard adjustment factors for weaning weight. Adjustment factors Age of dam Male calves Female calves

2 +60 +54 3 +40 +36 4 +20 +18

5-10 0 0 ≥11 +20 +18

Source: Beef Improvement Federation.

• Most Probable Producing Ability (MPPA) – This value should be included on produce-of-dam summaries. It is an estimate of the future productivity of that cow for calf weaning weight using past production records. The formula for MPPA is

(No. of calves) x 0.4 MPPA = 100 + 1 + (No. of calves – 1 ) x 0.4 x (Avg. weaning wt. ratio – 100)

• Yearling weight – This is important because of its relationship to efficiency and pounds trimmed retail boneless beef produced. Intensively managed cattle should be evaluated for yearling weight near 365 days. Less intensively managed cattle may be given a “long” yearling weight at 452 days or 550 days. Adjusted 365-day weight is computed as given below. Adjusted weights for 452 or 550 days are computed similarly, except 247 or 345 replaces 160 in the equation.

(Yearling wt. – Weaning wt.) Adj. 365 day wt. = Days between wts.

x 160 + adj. 205 day wt.

The yearling weight and weaning weight used are the actual weights taken at yearling (or long yearling) and weaning times. The number of days between weights represent the days between the times yearling weight and weaning weight were obtained. The first part of the equation gives the average daily gain from weaning to yearling age. This is multiplied times the number of days between 205 days and the target age (365, 452, or 550) being used for yearling weight to get expected total weight gain from 205 days to the final days. This total weight gain is added to the adjusted 205-day weight to get the adjusted yearling weight. The age of dam adjustment is already included with the adjusted 205-day weight.

• Postweaning feed efficiency – This is difficult to measure accurately, even in groups, and is expensive to evaluate in individual cattle. For either weight-constant or time-constant end


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points, faster gaining cattle have better feed efficiency. Selection for increased growth rate is important but must be tempered because of its correlation with mature size. Carcass Evaluation. Edible beef products are

the goal of all beef cattle improvement programs. Complete carcass evaluation includes measures of both quantity and quality of lean product. Not all beef producers will need complete carcass information and the economic importance of the carcass information is variable. Increasing the amount of data on large numbers of cattle adds to the time required as well as the cost of the performance program. When carcass data are desired, the following procedures are recommended: • Product Quality – This represents the visual

appearance and palatability component of the carcass evaluation. The grades are Prime, Choice, Select, and Standard. An evaluator assigns the grades using visual evaluation. The criteria include physiological maturity, marbling, color, firmness, and texture of lean.

• Maturity – An estimation of the physiological age of the carcass. It is determined by evaluating the size, shape, and ossification of the bones and cartilages, and the color and texture of the lean meat. Maturity is classified into these groups.

Maturity A – 9 to 30 months Maturity B – 30 to 42 months Maturity C – 42 to 72 months Maturity D – 72 to 96 months Maturity E – over 96 months

• Marbling – The flecks of fat in the lean. This is the primary factor determining quality grade after maturity is determined. It is evaluated visually in the ribeye muscle, between the 12th and 13th ribs. Marbling contributes to meat tenderness and is associated with palatability traits of “juiciness” and “flavor.” There are 9 degrees of marbling ranging from “devoid” to “abundant.” Intramuscular fat percentages range from 2.76% for traces to 10.13% for slightly abundant. Quality grade and marbling are associated in young cattle as follows:

Prime – abundant, moderately abundant, slightly abundant

Choice – moderate, modest, small Select – slight Standard – traces, practically devoid

• Color, firmness, and texture – These are used to characterize the lean tissue. The following scoring system is recommended (Table 20.8):

Table 20.8 –Scores for lean tissue. Score Color Firmness Texture

7 Light cherry red Very firm Very fine 6 Cherry red Firm Fine 5 Slightly dark red Moderately firm Moderately fine 4 Moderately dark red Slightly soft Slightly fine 3 Dark red Soft Slightly coarse 2 Very dark red Very soft Coarse 1 Black Extremely soft Very coarse


• Yield grade – This is a method for evaluating the yield of salable meat. The formula for yield grade is USDA Yield Grade = 2.50 + (2.5 x adjusted fat thickness, in.) + (0.2 x kidney, pelvic and heart fat, %) + (0.0038 x hot carcass weight, lb) – (0.32 x ribeye area, sq. in.)

• Adjusted fat thickness – This measurement is taken at the 12th rib at three-fourths of the distance of the ribeye from the backbone. An adjustment is allowed for unusual fat distribution.

• Kidney, pelvic, and heart fat percent – This is an estimate of fat located in the kidney knob, pelvic, and heart regions. The estimate is recorded as a percentage of the carcass weight.

• Ribeye area – This is measured at the 12th rib and indicates the amount of muscling in the carcass.

• Hot carcass weight – This is the weight of the carcass as it leaves the harvest floor.

Live Animal Evaluation Evaluation of live animals takes into

consideration any measurements or subjective evaluations that help describe an animal. For example, breeding soundness evaluation involves physical examination of bulls to include penis, rectal examination of internal reproductive organs, and scrotum. Some other common measurements of cattle include backfat, pelvic size, height at the shoulder, height at the hip, and body length. In recent years, measurements for height have become a descriptive supplement to many herd testing programs. Adjusted weights and weight ratios accompanied by linear measurements for height have added another dimension to evaluating the fat-lean ratio of an individual animal in a performance program. A linear measurement should never be interpreted as a replacement for the weight of an animal at a given age. Instead, linear measurements should be used with growth information as a supplement for selection. No one frame size for an


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animal will be best for all feed resources, breeding systems, and feed costs. The recommended procedures for obtaining hip height are • Frame score – This is a convenient way of

describing the skeletal size of cattle. It is simply a classification system for hip heights that is set up to be descriptive throughout the animal’s growth phase. The recommended point for hip height is a point directly over the hooks. This measurement is adjusted to 205 or 365 days of age and should be adjusted for age of dam. Hip height is generally expressed in inches. The age of dam adjustments are shown in Table 20.9. Table 20.9 – Age of dam adjustment factors for hip height. Age of dam Male calves Female calves

2 and > 12 1.02 1.02 3 and 12 1.015 1.015 4 and 11 1.01 1.01 5 to 10 1.00 1.00

To adjust to 205 days, (1) multiply the number of days under 205 by .033 for bulls or .025 for heifers, and add to the actual height; or (2) multiply the number of days over 205 by .033 for bulls or .025 for heifers and subtract the result from the actual height. To adjust for age of dam, multiply the adjusted height by the appropriate age-of-dam factor.

Adjustment to 365 days is done in a similar manner as follows:

Bulls Adj. Height = actual height + (days under 365 x 0.033)

or Adj. Height = actual height – (days over 365 x 0.025) Heifers Adj. Height = actual height + (days under 365 x .025)

or Adj. Height = actual height – (days over 365 x .025) The frame score is calculated with the following formulas (actual heights and ages): Frame score in bulls = – 11.548 + 0.4878 (hip height) –

0.0289 (days of age) + 0.00001947 (days of age)2 + 0.0000334 (hip height) (days of age)

Frame score in heifers = – 11.7086 + 0.4723 (hip height) –

0.0239 (days of age) + 0.0000146 (days of age)2 + 0.0000759 (hip height) (days of age)

• Scrotal circumference – This measurement is an

indicator of both sperm production and age at puberty. Using a flexible tape, measure the

largest diameter portion of the scrotum. The bull’s scrotal measurement in centimeters, the bull’s age, and the appropriate adjustment factor (Table 20.10) are applied to formula below to determine the 365-day scrotal circumference. Adj. 365 day yearling scrotal circumference = Scrotal circumference + [(365 – age) x Age adj. factor]

Table 20.10 – Age adjustment factors for scrotal circumference. Breed Adjustment

Factor

Angus .0374 Red Angus .0324 Brangus .0708 Charolais .0505 Gelbvieh .0505 Hereford .0425 Polled Hereford .0305 Limousin .0590 Salers .0574 Simmental .0543

Source: Geske, J.M.

• Pelvic area – This is an indicator of calving difficulty (dystocia) in young heifers. In first calf heifers, yearling pelvic area serves as a culling tool to remove heifers at risk for calving problems. The ideal time to take pelvic measures is between 320 and 410 days of age. A qualified technician or veterinarian should record the vertical and horizontal dimensions of the pelvis to determine the area.

Bull adj. 365 day pelvic area = Actual pelvic area (cm2) + [0.25 x (365 – Age in days)] Heifer adj. 365 day pelvic area = Actual pelvic area (cm2) + [0.27 x (365 – Age in days)]

• Behavior – This trait is an assessment of an animal’s response to handling and management. It is measured using a subjective scoring system listed in Table 20.11 and evaluates differences in disposition when animals are being worked in a squeeze chute. The trait is measured at weaning or yearling age to prevent any biases due to the animal’s prior experiences.

Bull Test Stations Numerous bull testing stations are located in the

United States. Many of these have been in operation for more than 30 years. Thousands of bulls have been tested in such facilities. Many of these bulls have gone into the commercial industry. Commercial


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Table 20.11 – Disposition scoring system for beef cattle. Score Description

1-Docile Gentle, undisturbed, and exits chute calmly.

2-Restless Quieter than average, attempts to back out of chute, exits chute promptly

3-Nervous Temperament is manageable, but animal is nervous. A moderate amount of struggling and exits the chute quickly.

4-Flighty Jumpy and out of control. Exhibits froth at mouth and bellows. Runs fence line and tries to jump out of pen.

5-Aggressive May be similar to a score of 4 with additional aggression. Exits chute quickly and may exhibit overly aggressive behavior

6-Very Aggressive

Very aggressive behavior and exhibits a wild behavior when confined in a small place.


cattle producers have long recognized the bull test station as a source of quality bulls that have some performance evaluation. BIF guidelines for full feed central bull test stations follows:

• Age of calves at delivery to test stations should be at least 180 days and not more than 270 days. Comparisons between bulls should be in contemporary groups within 90-day age spread.

• Herds from which bulls are consigned should be on a herd testing program.

• The following should be submitted to the station: sire, birth date, birth weight, age of dam, and EPD.

• There should be an adjustment period of at least 21 days prior to the test period.

• The length of the feeding test should be at least 112 days.

Initial and final test weights may be either full or shrunk weights. If full weights are taken, they should be the average of two weights taken on successive days to minimize fill effect.

Expected progeny differences should be reported on final test reports for traits available (for example, birth weight, weaning weight, yearling weight, and milk).

Yearling ultrasound measurements should be recorded at the end of the test. This activity should take place when the average age of the pen is 365 days.

All bulls sold in a test should be examined for reproductive and structural soundness. A qualified

veterinarian or technician should conduct the breeding soundness examination.

Feeding should be free choice and rations should be between 60 and 70% total digestible nutrients (TDN).

The nutrition program should meet the growth requirements of bulls on test. Therefore, it is important for the ration to provide adequate levels of protein and energy for growing bulls.

Many of the recommendations previously described are applied to full feed bull test stations. There are guidelines available through BIF to evaluate cattle in a forage-based bull test facility (See BIF Guidelines, Central Bull Test Stations).

The most useful trait measured in a test station is the 112- or 140-day average daily gain since this trait is measured over the period the bull is at the test station. Many test stations also provide information on weaning weight, yearling weight, hip height, and scrotal circumference since these are either made available to the station upon entry of the bulls or can be measured while the bulls are in the station. Average daily gain and yearling weight should be expressed in the station report as ratios so that comparisons among bulls can be made easily. The comparison of animals from different test stations or animals evaluated at different times is not valid. Animals should only be compared within a test group.

GENETIC PREDICTIONi

Genetic prediction is a common catch phrase used in the rapidly evolving field of beef cattle improvement. The concept of performance evaluation of beef cattle began over 50 years ago. The beef cattle industry has been following the model of dairy cattle genetic improvement in that techniques for identification of superior cattle and procedures for on-farm testing and sire evaluation were developed. The use of the “Animal Model” has meant that we are now performing “National Cattle Evaluation” where all individuals, male or female, can have an estimate of genetic merit assigned to them. The term “Genetic Prediction” comes from the fact that current techniques allow more than simple evaluation. We are predicting the future as superior sires and dams are identified and used in breeding programs.

EXPECTED PROGENCY DIFFERENCE (EPD)

Most beef breed associations express estimated breeding value as an Expected Progeny Difference


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(EPD). EPD is also one-half of the breeding value relative to all other bulls in the program. The EPD is simply the difference that is expected in the offspring of a particular individual relative to some base point. It makes the most sense when two individuals are being compared directly. For example, consider two bulls: Sire A has an EPD of +25 and Sire B has an EPD of -10. We should expect the calves by Sire A to be 35 lb heavier than calves from Sire B, if all calves are managed in a uniform manner and are out of cows of similar genetic merit. In most cases, the EPD is given as a positive or negative value in the units of measure for the particular traits, although there are exceptions.

Each member of a breed can have EPD values calculated for it. Age, sex, or status as a parent are not limiting factors. Even a new born calf could be assigned EPDs. It is possible to compare any two members of the breed, regardless of location. It is frequently said that an EPD is a comparison to an average bull. Unfortunately this is not completely true. A zero EPD represents the average genetic merit of animals in the database at the time when there was sufficient information to calculate EPDs or at a time designated by the breed association. It, therefore, represents an historic base point. If the breed has made any genetic change for a trait, the average will no longer be zero. More breed associations publish the average EPDs or a table showing percentile groups. This should be examined carefully before individual EPDs are studied.

CONTEMPORARY GROUPS Each trait has both a genetic and environmental

component that contributes to the observation of the trait for an animal. The development of genetic predictions, such as EPD, depends on the ability to determine what portion of the performance is genetic compared to environmental and reduce the impact of the environmental effects on a trait. As an example, weaning weight in cattle is affected by several environmental factors and mathematical adjustments are used to reduce the influence of those effects. It is well known that calves sired by mature cows are more likely to be heavier at weaning time relative to calves from first calf heifers. Other adjustments include sex of the animal and age effects. But, how are effects of feeding environment, management differences, and weather taken into account? Are mathematical adjustments available?

There are no reliable mathematical adjustments for weather or differences in feed environment.

Therefore, a contemporary group is formed to compare animals that experienced similar environmental effects. The proper formation of contemporary groups improves the quality and effectiveness of EPD as a selection tool. The BIF defines a contemporary group as a group of cattle that are of the same breed composition and sex, are similar in age, and have been raised under the same management conditions.

Examples of Contemporary Group Information from the 2002 BIF Guidelines:

Birth Weight • Breeder/herd code • Year • Season (Fall or Spring) • Sex of animal (bull or heifer) • Breed composition • Management codes • Service type

Weaning Weight • Birth contemporary group • Management/pasture code • Date of weaning weight • Weaning sex (bull, heifers, or steer)

Pedigree Estimated EPD Many sale catalogs will contain EPDs for the

bulls offered for sale. Some bulls will appear in catalogs with limited or no EPD information. This may be particularly true for young bulls that have not yet had their performance information included in the breed genetic evaluation. Bull buyers may use a quick and easy procedure to compute “Pedigree EPD” values for young bulls with no EPDs. Pedigree EPDs may be computed using EPDs on the animals in the pedigree of the young bull.

Every calf receives a random sample half of the sire’s genes and a random sample half of the dam’s genes to combine into the complete genetic makeup of the calf. Parents of the calf received their genetic makeup in the same fashion, with half of their genetic makeup contributed by each parent. By understanding this halving nature of inheritance, the EPDs on parents and grandparents in the pedigree of a young bull may be used to compute Pedigree EPDs.

Procedure to calculate Pedigree EPD: The first step in calculating the Pedigree EPD for a young bull is to determine how much EPD information is available on the animals in the pedigree of the bull.


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Many times, the breeder of the young bull will supply a performance pedigree including EPDs for the sire, maternal grandsire (MGS), maternal great grandsire (MGGS), and maybe even the dam of the young bull.

An example calculation of the Pedigree EPD:

1. If both sire and dam of the young bull have EPDs, take one-half the EPD of each parent. Ped. EPD = ½ EPD of Sire + ½ EPD of Dam

2. If the EPD on the dam is missing, you may use EPDs on her relatives. Ped. EPD = ½ EPD of Sire + (½)2 EPD of MGS = ½ EPD of Sire + ¼ EPD of MGS

3. Another option is to use the maternal great grandsire (MGGS) information, too. Ped. EPD = ½ EPD of Sire + (½)2 EPD of MGS + (½)3 of MGGS = ½ EPD of Sire + ¼ EPD of MGS + ⅛ EPD of MGGS

Note: If the EPD of the Dam is known, then you cannot use the EPD information on the MGS and MGGS.

Knowing the procedure to compute Pedigree EPDs may be useful in selecting young bulls with no EPDs available. By taking advantage of performance information available on the parents and grandparents, quick calculations give you Pedigree EPDs on bulls for use as a selection tool. Some breed associations have an “Interim EPD” program based on pedigree information to provide EPDs on young animals that have not had an opportunity to have their individual performance included in the most recent national cattle evaluation for the breed. Many sale catalogs may already give you the Pedigree EPD for convenience.

Interim EPD A majority of breed associations will generate

their EPD once per year; however, a few breeds will update their EPD twice a year. A majority of producers will submit their data to coincide with these fall and spring updates, but some will send their data between EPD analyses. Because the information is valuable to improving the reliability of an animal’s EPD, researchers developed Interim EPD. Breed associations produce Interim EPD with existing parental EPDs combined with recently collected data on the animal of interest. This is a common occurrence with post-weaning information, where a calf has a pedigree EPD estimate for yearling weight and additional data are collected

between genetic evaluations. A breed association can use the past and present information to calculate a more accurate interim EPD.

Across Breed EPD The comparison of animals using EPD is feasible

within breed and across herds. However, it is not appropriate to directly compare the EPD of an Angus with a Hereford because each breed generates their EPD separately, unless the EPD are adjusted using appropriate adjustment factors. The U.S. Meat Animal Research Center (MARC) in Clay Center Nebraska conducts research to estimate the appropriate breed specific adjustment factors and labels them across breed EPD (AB-EPD). The updates for the AB-EPD are completed each year using research data from the MARC and the appropriate breed association (Table 20.12). Table 20.12 – Adjustment factors to add to EPDs to estimate across breed EPDs.

Breed Birth wt. Weaning wt. Yearling wt. Milk Angus 0.0 0.0 0.0 0.0 Hereford 3.3 -2.4 -15.1 -16.2 Red Angus 3.6 -1.2 -0.1 -10.7 Shorthorn 7.8 31.2 44.5 12.0 S. Devon 6.7 21.5 40.5 2.1 Brahman 13.0 34.7 -5.5 26.1 Limousin 5.8 23.5 20.5 0.2 Simmental 6.4 21.6 21.1 9.0 Charolais 10.5 41.1 57.8 2.0 Gelbvieh 5.3 7.9 -20.3 3.8 Maine Anjou 6.6 17.9 5.9 8.0 Salers 5.1 28.4 40.6 11.3 Pinzgauer 7.7 28.2 24.9 6.0 Tarentaise 3.6 29.8 12.8 17.8 Braunvieh 6.6 30.3 13.5 23.1 Brangus 5.7 20.1 11.1 --- Beefmaster 9.9 38.5 29.7 ---


According to the MARC, the AB-EPD are best used in crossbreeding programs with multiple breeds. AB-EPD can be used to improve the crossbreeding program design and avoid problems with mis-matching animals with inappropriate EPD for certain traits. The example in Table 20.13 illustrates the use of AB-EPD. In this example, a producer uses two breeds, Angus and Gelbvieh, in a rotational crossbreeding system. If a producer is interested in uniformity of sires for multiple traits, the AB-EPD can assist the comparison of sires by adjusting the breed specific EPD to a common AB-EPD. The AB-EPD adjustment factors are useful for other breeding program designs such as a terminal crossbreeding system.


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Table 20.13 – Comparison of two sires using across breed EPD adjustment factors.

BW WW YW Milk

Sire A-Angus Angus EPD 1.0 25.0 50.0 10.0 Adj. Factor 0.0 0.0 0.0 0.0 AB-EPD 1.0 25.0 50.0 10.0

Sire B-Gelbvieh Gelbvieh EPD 1.0 25.0 50.0 10.0 Adj. Factor 5.3 7.9 -20.3 3.8 AB-EPD 6.3 32.9 29.7 13.8

How accurate are the AB-EPD? The accuracy of any EPD is not perfect for animals within a breed and the level of accuracy depends on factors such as type and amount of data, and the heritability of the trait. BIF Guidelines states the accuracy of the AB-EPD will be determined from the accuracy values within breed and accuracy of breed differences. It is recommended to use the lowest within breed accuracy levels for the AB-EPD accuracy levels.

Accuracy Each EPD value should have an accuracy

assigned to it. The accuracy is a measure of confidence in the EPD. It is expressed as a value between zero and one. A high accuracy (>0.7) means that we are very confident in the EPD and it is not expected to change much as further information is gathered. A low accuracy (<0.4) means that the EPD may change a great deal as additional information is gathered. Non-parent animals have lower accuracy values since no progeny information contributes to their EPD. From a practical standpoint, the EPDs are used to select bulls for use in the herd, and accuracies help determine how extensively to use the bulls in the herd.

Possible Change An EPD value is a prediction that can change

with addition of information. As previously described, accuracy is an assessment of the confidence in an animal’s EPD value; however, possible change is an alternative way to express future change for an EPD. Possible change is the measure of the potential error associated with EPD values. Most sire summaries include such values. Possible change is expressed as “±” the appropriate units of EPD. These values quantify the amount a certain EPD may deviate from the “true” progeny difference. In fact, accuracy and possible change values share a relationship. As more information is accumulated, accuracy increases and possible change

decreases. For a given accuracy, the “true” progeny difference of 68% of all animals evaluated (within breed) are expected to fall within the plus or minus one possible change value. An example to illustrate this point is in Table 20.14. Table 20.14 – EPD, accuracy (ACC), possible change (PC), and confidence ranges (CR) for sires A and B.

Sire BW WW YW

A EPD 2.0 30 70 ACC 0.5 0.5 0.5 PC ± 1.5 ± 6.0 ± 8.0 68% CR 0.5 to 3.5 24 to 36 62 to 78

B EPD 1.0 40 60 ACC 0.9 0.9 0.9 PC ± 0.3 ± 1.0 ± 2.0 68% CR 0.7 to 1.3 39 to 41 58 to 62

Of all the animals with the EPD and accuracy levels in Table 20.14, two-thirds of the animals are expected to have “true” progeny differences inside the 68% confidence range. For example, the probability the “true” progeny difference for birth weight on sire “B” is between 0.7 and 1.3 is 68%. These “true” differences have a much greater chance of falling toward the center of the range defined by the possible change value than falling close to the extremes.

Also, one-third of the individuals in the evaluation may have their “true” values fall outside the 68% confidence range. In our previous example, one-sixth of the individuals may have “true” values less than +0.7 and one-sixth of the individuals may have “true” values more than +1.3.

Producers assume a certain level of risk when they make a selection decision; however, the risk is manageable. Accuracy and possible change are useful tools to determine the risk in selection decisions. For example, a low risk beef producer would be more likely to use a sire with high levels of accuracy and lower levels of possible change. A risk-oriented producer would select a sire with lower levels of accuracy and extreme EPD values.

Animal Model Most breed associations use Animal Model

(AM) or Reduced Animal Model (RAM) procedures to compute EPDs. Each individual has its own performance and the performance of progeny, siblings, parents, grandparents, etc., that could be utilized to evaluate genetic merit. Animal Breeding technology, as well as a new generation of computers, brought about the use of an AM. This class of model provides techniques whereby the


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performance of the animal itself, as well as all available information on relatives is included in the estimate of genetic merit. As a result, EPDs are already available on parent and nonparent animals. This process involves extensive calculations that only the latest generation of computers is able to accomplish efficiently.

Use of an AM has some very beneficial features. EPDs are available for all animals, male and female. Preferential mating of certain individuals does not bias the results. Therefore, that expensive bull can be used only on genetically superior cows and his EPD will not be inflated. This is accomplished by adjusting for the EPDs of the cows to which he is mated. Use of an AM makes appropriate adjustments for genetic trend. Additionally, the AM can account for both direct and maternal contributions to a trait, such as direct and maternal components of weaning weight.

New advancements in AM technology have improved EPD development. Many trait EPDs are developed using both the trait of interest and correlated traits. A multiple trait model generates EPDs that account for culling bias due to poor performance and accuracy levels increase for the trait of interest. Additionally, several new EPDs are available for traits, such as heifer pregnancy and disposition, because of a new class of categorical trait models.

Milk EPD Weaning weight can be defined by the genes for

growth in the calf and genes for milk (mothering ability) in the cow. There are separate EPD values for these two components. The Weaning Weight EPD evaluates genetic merit for growth and the Milk EPD evaluates genetic merit for mothering ability.

The Milk EPD that results from the separation of weaning weight into growth and milk segments is, like any other EPD, fairly simple to use. It is the expected difference in weight of calves out of cows by a particular sire, due to differences in mothering ability. As an example, consider two bulls: Sire A has a Milk EPD of +10; Sire B has a Milk EPD of –5. The expected weaning weight difference, due to mothering ability alone, in calves out of daughters by the two bulls is 15 lb.

SIRE SUMMARIES Sire summaries include a sampling of the

available genetic material in each breed. The summaries for breeds that conduct National Cattle

Evaluations come out at least once a year. Summaries include graphs of the average change in EPD for the particular breed. Descriptive material written at the first of each summary describes the format for reporting the EPDs.

At least 23 beef breed associations currently conduct cattle evaluation programs. These programs are briefly summarized in Tables 20.15, Table 20.16, and Table 20.17.

Note that almost all sire summaries include birth weight, weaning weight, yearling weight, and milk (Table 20.15). A few currently include some characteristics that have a role in reproduction such as calving ease, gestation length, heifer pregnancy, stayability, and scrotal circumference (Table 20.16). Many of the breeds are currently looking at beginning to include some of these other characteristics into the summaries. A larger number of breeds are continuing to develop end-product traits using both carcass and ultrasound data (Table 20.17). This has resulted from the high degree of interest in “specification beef.”

Many of the summaries contain two listings of bulls. The first is a listing of progeny proven bulls. These are older bulls that have calves with performance records. Therefore, the accuracies on the birth and weaning weight EPDs are generally at least 0.6. The second section is devoted to younger bulls that have lower accuracies (0.3 to 0.5 on weaning and birth weight). The criteria for listing vary among the breeds. These younger bulls are sometimes called “Genetic Resource” sires.

USE OF EPDs FOR SELECTION IN PUREBRED HERDS

Purebred producers need to consider EPDs in their breeding programs. Competitors are using them and genetic change is happening. Care needs to be exercised when making selection decisions. Type fads have caused some problems in the past when single traits are emphasized. Similar or worse problems may arise if a single performance trait is emphasized. For example, if the members of a breed association emphasize yearling weight, and ignore all other characteristics, several concerns may result. Birth weight would be expected to increase, with the attendant calving difficulty. Mature size should also increase, perhaps to the point where the functionality of the cow herd would diminish. This could also lead to problems in reaching desirable quality grade at an acceptable weight. Each trait has a set of drawbacks


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Table 20.15 – Summary of growth and mature size EPD from multiple U.S. beef cattle breed associations genetic evaluations. Breed Birth Weaning Milk Total Yearling Mature Mature

Angus X X X X X X X Beefmaster X X X X Braford X X X X X Brangus X X X Braunvieh X X X X X Blonde d’Aquitaine X X X X X Brahman X X X X Charolais X X X X X Gelbvieh X X X X X Hereford X X X X X Limousin X X X X Red Angus X X X X X Red Brangus X X X X X Romagnola X X X X X Salers X X X X X Santa Gertrudis X X X X X Senepol X X X X X Shorthorn X X X X X Simbrah X X X X X X X Simmental X X X X X X X South Devon X X X X X Tarentaise X X X X X Wagyu X X

Source: Center for Genetic Evaluation of Livestock, Colorado State University.

Table 20.16 – Summary of reproductive EPD from multiple U.S. beef cattle breed associations genetic evaluations.

Breed Calving

Ease Calving Ease

Daughters Docility Gestation

Length Heifer

Pregnancy Scrotal

Circ. Stayability

Angus X X Beefmaster X Brangus X Charolais X Gelbvieh X X X X X Hereford X X X Limousin X X X X Red Angus X X X X Salers X X X Shorthorn X X X Simbrah Simmental X X Tarentaise X

Source: Center for Genetic Evaluation of Livestock, Colorado State University.

Table 20.17 – Summary of end product EPD from multiple U.S. beef cattle breed associations genetic evaluations.

Breed Fat

Thickness Marbling

Score Rib Eye

Area Carcass Weight Tenderness

Retail Yield %

Grid Merit

Angusa X X X X X Brangus X X Charolais X X X X Gelbvieh X X X X X Hereford X X X Limousin X X X X Red Angus X X X Salers X X X X X Senepol X X X Shorthorn X X X X X Simbrah X X X X X X Simmental X X X X X X South Devon X X X Wagyu X X X a American Angus Association publishes separate EPD for ultrasound traits. Source: Center for Genetic Evaluation of Livestock, Colorado State University.


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if changes are carried to an extreme. The availability of EPDs make extremes easier to reach if breeders chose to blindly emphasize a single trait.

A more balanced selection program is desirable and uses EPD to effectively reduce risk of selection decisions. Some producers recommend choosing herd sires that have high yearling weight EPD, high milk EPD, and low birth weight EPD. These three characteristics are sufficiently different that the difficulties from extreme changes in any one of them would be unlikely. Many important traits are not included in a large number of breed sire summaries. Careful monitoring of reproductive performance, including conception rates, calf mortality, libido in bulls, and regularity of calving, is still critically important. Carcass characteristics have increased importance and breeders are certainly encouraged to obtain whatever carcass data is feasible and use it to make selection decisions. Carcass EPDs are available in several breeds. For several years, many breed associations have endorsed ultrasound data collection as a supplement to carcass data.

Purebred breeders should avail themselves of the opportunity to obtain EPDs on each herd member if their association provides this service. Most associations have this ability. Even though the accuracies are sometimes low on these EPDs, they should be used when choosing replacements and, if possible, when culling cows.

Purebred producers are not only the users of EPDs, but they also provide the data used in predicting EPDs. Producers are encouraged strongly to provide complete, accurate records on all calves born each year. Complete, accurate record keeping is the only way that useful and unbiased EPDs can be calculated. EPDs for the Commercial Producer

It will be the rare commercial producer who uses bulls listed in a breed association’s sire summary. What then should be done about EPDs? Many breed associations have a mechanism in place where individual purebred producers can obtain EPDs on herd individuals. Commercial producers should demand such information from their purebred sources of breeding stock.

A commercial producer has a first responsibility of choosing the appropriate breed or breeds for the program. Once breeds are chosen, replacement breeding stock needs must be examined. Some recommendations are shown in Table 20.18.

Each of these recommendations should be followed with an awareness of the prevailing conditions. Rougher conditions probably dictate avoidance of very high EPDs for growth and/or milk and even more care to avoid high birth weights. Growth EPDs should be geared to the desires of the potential buyers and marketing opportunities. Again, traits for which there are a limited number of EPDs can also be important. Traits associated with reproduction certainly fall into this category and a select few associations publish EPDs for reproductive traits (see Table 20.16). Commercial producers should demand that bulls have passed a breeding soundness examination. The cow herd of the seller should be examined for regularity of calving.

EPDs within a breed are directly comparable between herds. Therefore, if a commercial producer has more than one source of breeding stock, he/she can compare the genetic merit of the different sources. Unfortunately, EPDs cannot be directly compared between breeds. A bull with a low birth weight EPD from a large mature size breed may sire calves that are heavier than a bull with a high birth weight EPD from a moderate sized breed. A low birth weight EPD does not guarantee a minimum of calving difficulty if the choice of breeds is incorrect. However, a commercial producer should use the USDA Meat Animal Research Center Across Breed EPD table mentioned previously to compare bulls from different breeds (Table 20.12).

MATING SYSTEMS Inbreeding

Inbreeding is defined as the mating of individuals that are more closely related than the average of the population from which they came. The primary genetic effect of inbreeding is to increase the number of homozygous gene pairs and decrease the number of heterozygous gene pairs. With the increase in homozygosity, inbreeding

Table 20.18 – Recommendations for EPD for various commercial scenarios. Use of Individual Breed Size Birth Weaning Yearling Milk

Terminal sire on mature cows Lg. carcass Not too high High High Not relevant Bull to use with heifers Sm. - med. Low Moderate Moderate Moderate - high, if keeping heifers Sire replacement heifers Med. maternal Low - moderate Moderate - high Moderate- high Moderate - high


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brings to light undesirable recessive genes and tends to bring about a decline in average phenotypic performance for various traits. This decline in performance is labeled inbreeding depression and it is well documented in the scientific literature. Inbreeding depression has the largest effect on lower heritability traits and the impact declines with increases in heritability. Inbreeding depression is the opposite effect of heterosis, which is the advantage gained from crossing lines or breeds. But, inbreeding does not create undesirable recessive genes.

The method used to determine the level of inbreeding is the inbreeding coefficient. The inbreeding coefficient measures the percent increase in homozygous gene pairs in an individual relative to the average of the population from which the individual came. If a bull has an inbreeding coefficient of 0.25, he is expected to have 25% more homozygous gene pairs than a non-inbred individual from the same population. The range of inbreeding coefficient values is 0 to 1.0.

Inbreeding can be used to concentrate the use of a genetically superior individual (linebreeding). Historically, producers used inbreeding to develop lines of inbred cattle. The principle is analogous to the inbred lines in the crop and poultry industries. Another use of inbreeding would be to critically evaluate an individual before forming a breeding program around that individual (for example, testing for undesirable recessive genes). Inbreeding is utilized primarily in herds with high genetic merit, which are devoted to production of breeding stock. Inbreeding practices have both beneficial and detrimental effects; therefore, the implementation of it should be weighed.

Crossbreeding Crossbreeding, which is the mating of

individuals with different breed makeup, is widely used in commercial beef production. It should be used by all commercial producers since improvement in efficiency can be dramatic if appropriate breeds are used. Crossbreeding does not eliminate the need for outstanding purebred livestock since efficient systems require knowledge of the purebred foundations being used.

The benefits of crossbreeding are twofold. Heterosis is the average superiority of a crossbred individual over the average of breeds involved in the cross. Breed complementarity is the advantage gained from using an optimum combination of breeds. Different types of crossbreeding systems use different levels of these two benefits.

Heterosis Heterosis arises from combining genes from

different breeds such that inferior recessive genes are concealed. Heterosis may result in the crossbred being better than either parental breed or simply better than the average of the two. For example, an Angus x Hereford crossbred calf will generally grow faster than either Angus or Hereford purebreds.

Heterosis arises from three mating situations. Individual heterosis is the advantage of the crossbred individual relative to purebred individuals. Maternal heterosis is the advantage of the crossbred mother over the average of purebred mothers. For example a Hereford x Angus cow is generally a better mother than the average of purebred Herefords and Angus. Paternal heterosis is the advantage of a crossbred male over the average of purebred males. Paternal heterosis generally only has an effect on testis characteristics and conception rate. The male does not have any direct effect on growth or survival as does the female so the benefits are more limited. However, particularly if young males are being used, the benefit in added conception rate can be large.

Heterosis levels can be generally grouped into three major classes. Reproductive traits generally show fairly high levels of heterosis. Growth traits generally have moderate levels of heterosis while carcass traits infrequently display much heterosis. There are exceptions to these but the three classes work as a general rule of thumb. It should be pointed out that this is exactly the reverse of the general levels of heritability for these classes of traits (Table 20.19). Table 20.20 presents information on percent heterosis for beef cattle traits from papers which combined information from crossbreeding experiments at several locations. Table 20.19 – Summary of total heterosis by type of trait.

Trait Heritability Total Heterosis Carcass Measurements Skeletal Measurements High Low (0 to 5%) Mature weight Growth Rate Early weights Medium Medium (5 to 10%) Milk production Maternal Ability Reproduction Health Low High (10 to 30%) Cow Longevity Overall Production

Source: Kress, D.D., and M.D. MacNeil.


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Table 20.20 – Heterosis in beef cattle. Heterosis (%) Trait Individual Maternal

Calving percentage 3.4 6.6 Calf survival 1.7 2.0 Birth weight 2.7 1.6 Weaning weight 4.7 4.2 Postweaning ADG (feedlot) 3.9 -1.4 Postweaning ADG (pasture) 6.4 - Yearling weight (feedlot) 3.8 2.9 Yearling weight (pasture) 4.5 - Loin eye area 2.8 - Fat thickness 2.3 - Quality grade 0.7 - Dressing % 0.6 - Cutability % 0.6 -

Source: Long, C.R., 1980.

CROSSBREEDING SYSTEMS Crossbreeding systems fall into two general categories: terminal systems and rotational systems. Both systems have advantages and disadvantages for different types of producers. Large producers can also combine characteristics of each to capitalize on the advantages of both systems.

Terminal Crossbreeding Systems Terminal crossbreeding systems are such that a

specific breed(s) of sire is mated to a specific breed(s) of dam. For example, a Simmental bull mated to an Angus female constitutes a two-breed terminal cross. A Charolais bull mated to a Hereford-Angus cow is an example of a three-breed terminal cross. A four-breed terminal cross uses a two-breed bull mated to two-breed females so that four different breeds contribute to the resulting calf breed composition. All three of these systems use 100% of the individual heterosis. The three- and four-breed terminal crosses use 100% of the maternal heterosis. The four breed terminal cross also uses 100% of any paternal heterosis. Breed complementarity is the main advantage of terminal systems since male and female breeds can be chosen for specific roles. Any terminal cross should have a breed(s) of male that excels in growth and carcass merit and a breed(s) of female that is superior for reproductive performance and mothering ability.

Figure 20.1 illustrates the overall approach to the terminal cross system. Breeder 3 represents the terminal cross, and Breeder 1 and Breeder 2 are necessary to make the terminal cross system work. The Breeder 3 system is the only step at which maximum heterosis is realized. All of the calves in this step are market animals, thus the name terminal cross.

Breeder 1 could cross two breeds which place major emphasis on maternal traits such are reproductive fitness, milking ability, and longevity. Breeder 2 serves as a bull source for Breeder 3 and would emphasize growth rate and efficiency. Breeder 3 has the advantage of generating 100% of the possible heterosis and provides an opportunity to take maximum advantage of breed complementarity.

A variation to the system illustrated in Figure 20.1 could be that one producer, rather than the three breeders, carry out the steps. However, the size of the operation would need to be large to produce replacement females and sires for the terminal cross system.

Figure 20.1 – Terminal cross system.

Aside from maximum use of heterosis and breed complementarity, the terminal systems are also easy to use in that only one breed of male is being used at a time. As a result, only one breeding pen or pasture is needed. Any size operation can effectively use a terminal system as long as the replacements can be obtained. This, however, leads to the big disadvantage of terminal systems. Replacements must be purchased, unless a segment of the herd is set aside for purebreds to generate replacements. Bringing in animals from outside the herd can introduce disease problems and it eliminates control over selection practices. It is important to have a source of replacement breeding stock, which is high in quality and relatively free of disease.

Rotational Crossbreeding Systems Rotational crossbreeding systems generate their

own replacement females. Each cycle uses a different breed of male from the previous one and some female offspring are kept from each cycle as replacements. An example of a two breed rotational (or criss-cross) system is shown in Table 20.21.


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Table 20.21 – Example of a two-breed rotational crossbreeding system.

Generation Breeds % of heterosis used Sire Dam Individual Maternal

1 Hereford Ha

Angus Ab 100 0

2 A H x A 50 100

3 H A x (HA) 75 50

4 A H x (A (HA)) 62.5 75

n Repeat rotation 66.67 66.67

a Hereford b Angus

Each generation the breed of sire changes. After the first mating there is always some element of backcrossing so that some heterosis is lost. After several generations the amount of heterosis retained will stabilize at 66.67% for both individual and maternal heterosis. The advantage of such a system is that female replacements are produced in the system so that disease problems would be reduced and the producer can exercise some selection pressure in choosing replacement females. At least some part of the heterosis will always be used although losses can be substantial. Figure 20.2 illustrates the two-breed rotation.

Figure 20.2 – Two-breed rotational system.

The chief disadvantage of a rotational system is that breed complementarity is not used. Each breed in the rotation needs to be somewhat adapted as both a sire and dam breed. Outstanding reproductive performance for a specific breed is not capitalized upon since, over time, each breed contributes equally to the sires and the dams. Also, any given year will include parts of several generations so that more than one breed of male needs to be maintained and at least one breeding pasture or pen for each breed of male will need to be used. This creates problems for small producers where it is possible that only one male is used at a time.

Rotational crossbreeding systems can include any number of breeds. An example of a three-breed rotational system is illustrated in Figure 20.3. The amount of heterosis retained increases with the number of breeds involved. A two breed rotation retains 2/3 (67%) of the individual and maternal heterosis. A three breed rotation retains 6/7 (86%) of the individual and maternal heterosis while a four breed rotation retains 14/15 (93%) of the heterosis. As the number of breeds increases, it becomes less important to follow the same breed order each cycle. The critical point is that each generation should use a different breed of male than the previous one.

Figure 20.3 – Three-breed rotational system.

Large producers can capitalize on some of the advantages of both terminal and rotational systems by producing replacement females in a rotation of breeds with outstanding maternal performance and mating older females to a male from a breed with good growth and carcass merit. Figure 20.4 illustrates a combination two-breed rotation and terminal crossbreeding system. For example, Hereford and Angus bulls could be mated to all females under the age of 5 to sire replacement females in a commercial herd. Cows over 5 years of age could then be mated to Charolais bulls with all offspring from the terminal crosses being sold. This system would use some breed complementarity since the terminal crosses would involve a growth and carcass breed (Charolais) and breeds that excel in maternal performance (Angus and Hereford). There would be 100% individual heterosis in the terminal portion of the herd, 67% individual heterosis in the rotation part of the herd and 67% maternal heterosis


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Figure 20.4 – Combination rotational-terminal system.

in the entire herd. The cows would also be older before using a large breed of bull so calving difficulties should be minimized.

Such a system has the large disadvantage of being difficult to maintain. It requires a rather large herd for efficient utilization of the males and it requires segmenting the herd into small components, which may be difficult for some producers. The terminal and rotational portions of the herd would constitute about half of the herd.

For any type of crossbreeding system, the choice of breeds is vitally important. There are large differences between breeds for many traits of economic importance. Breeding stock that are inferior or are used unwisely will cancel out benefits of heterosis. Each producer should carefully consider the breeds that are readily available, design a system that can be used effectively with those breeds and be careful not to deviate far from the plan.

COMPOSITES Commercial cattle producers are often frustrated

by textbook crossbreeding systems (rotational). The source of the frustration originates from the added investment in fencing, labor, time, and facilities. If crossbreeding systems are well planned, there are favorable increases in both production and profitability. Unfortunately, poorly planned systems will yield frustration and possibly additional costs that outweigh the gains in production efficiency.

Composites and the mating systems associated with them are one alternative to the many crossbreeding systems available to producers. What

is a composite? Bourdon says, “A composite is a hybrid with at least two or more breeds in its background. Composites are expected to be bred to their own kind, retaining a level of hybrid vigor normally associated with traditional crossbreeding systems.”

A producer should carefully consider the characteristics of composite cattle before they choose to use them. Breeding the complete composite animal is very similar to purebreds or straightbreds. Only one breeding pasture is required and the composite herd generates replacement animals. Surprisingly, composite cattle retain a high level of hybrid vigor; however, the levels are less than observed in F1 cross cattle (Table 20.22). The amount of hybrid vigor is a function of the number of breeds in the composite. As for breed complementarity, the advantages are only realized during the development of a composite. In a 1999 USDA report from the Meat Animal Research Center, the consistency of composite animals was similar to purebred counterparts. This is often a surprise because consistency is sometimes judged by simply inherited traits like coat color.

Composite breeding systems are situation adaptable. Composite cattle breeding systems can be custom designed to a specific environment. For example, some commercial cattle producers have developed their own composites for their beef cattle enterprise because previous experiences with “traditional” crossbreeding systems proved ineffective. Additionally, a composite system can serve both the commercial and seedstock elements of the system.

Basic Formation of a Composite The development of a composite is an important

process and requires sufficient resources to do it properly. If a producer is not dedicated to the development process, they should purchase their composite cattle from a reputable breeder. However, it is important to understand the process to further one’s knowledge and abilities to identify correctly formed composite herds.

A well-formed composite occurs in multiple steps. The first step is between breed selections. During this step, a producer wants to identify the appropriate breeds and percentage of each breed in the composite system. A well-planned composite program will have information on the needs of the commercial producer, management, environment, and other factors impacting the performance of the


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final composite. The next step is within breed selection to identify appropriate foundation animals to construct the composite animals. It is important to identify a wide base of unrelated foundation animals and to avoid inbreeding at all costs. Increases in inbreeding levels will only reduce the level of hybrid vigor. Table 20.22. Hybrid vigor of different mating types and estimated increases in performance as a result of heterosis.

Mating Type

Retained Hybrid Vigor

Est. increase in weight weaned per cow exposed (%)

Pure breeds 0 0 Two breed rotation 66.7 15.5 Three breed rotation 85.7 20.0 Two-breed composite (1/2A, 1/2B)

50.0 11.6

Three-breed composite (1/2A, 1/4B, 1/4C)

62.5 14.6

Eight breed composite (1/8A, 1/8B, 1/8C, 1/8D, 1/8E, 1/8F, 1/8G, 1/8H)

87.5 20.4

Source: Gregory, Cundiff and Koch.

Breeding Composites The system of breeding a formed composite is

very similar to breeding purebred cattle. However, there are several important points for consideration to ensure the full advantage of the composite animal. The biggest concern is loss of hybrid vigor. A producer can avoid losses by having a large herd of animals (500 or more), cooperating with other breeders, avoiding linebreeding, and regularly reconstituting the composite.

CONCLUSION A good beef cattle producer takes time to admire

successes and evaluate mistakes. Successful producers focus their time and energy on sustainable and profitable beef production. In addition, they use their knowledge of beef cattle breeding principles combined with reliable selection methods to identify animals appropriate for their production system. They maintain detailed financial and performance records, and they regularly document the performance of their program. Performance programs, selection tools, and well-planned mating systems are available to assist beef producers with this process.

REFERENCES Beef Improvement Federation 35th Annual Research

Symposium and Annual Meeting. Lexington, Kentucky, May 2003.

Beef Improvement Federation and Guidelines. Guidelines for Uniform Beef Improvement Programs. Athens, GA. Retrieved from http://www.beefimprovement.org/.

Beef Improvement Federation and Guidelines. Guidelines for Uniform Beef Improvement Programs (8th Edition).

BEEF Magazine. Retrieved from http://beef-mag.com/.

Bourdon, R. (1985) Beef Cattle Breeding #6 – Terminology – EBVs, EPDs, ACCs, and PCs. Department of Animal Sciences. Colorado State University. Retrieved October 13, 2003 from http://ansci.colostate.edu/.

Bourdon, R. (1999) Composites 101. Department of Animal Sciences. Colorado State University. Retrieved October 13, 2003 from http://ansci.colostate.edu/.

Bourdon, R.M. (2000) Understanding Animal Breeding (2nd Edition). Prentice-Hall Inc., Upper Saddle River, NJ.

Buchanan, D.S. et al. (1993) Animal Breeding: Principles and Applications (4th Edition). Animal Science Department, Oklahoma State University.

Cundiff, L.V. and K.E. Gregory (1977) Beef Cattle Breeding. USDA Agricultural Information Bulletin 286.

Evans, J.L., and D. Davies (2002) Cow-Calf Production Record Software. OSU Extension Current Report 3279, Cooperative Extension Service, Oklahoma State University.

Frahm, R.R., and C.A. McPeake (1985) Crossbreeding Beef Cattle, I. OSU Extension Facts F-3150, Cooperative Extension Service, Oklahoma State University.

Frahm, R.R. (1982) Crossbreeding Beef Cattle, III. OSU Extension Facts F-3152, Cooperative Extension Service, Oklahoma State University.

Frahm, R.R. (1982) Crossbreeding Beef Cattle, IV. OSU Extension Facts F-3153, Cooperative Extension Service, Oklahoma State University.

Gregory, K.E., L.V. Cundiff, and R.M. Koch (1999) Composite Breeds to Use Heterosis and Breed Differences to Improve Efficiency of Beef Production. Roman L. Hruska U.S. Meat Animal Research Center Agriculture Research Service, USDA in Cooperation with the Institute of

http://www.beefimprovement.org

http://beef-mag.com/

http://ansci.colostate.edu/

http://ansci.colostate.edu/


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Agriculture and Natural Resources, University of Nebraska, Lincoln.

Kress, D.D., and M.D. MacNeil (1999) Crossbreeding Beef Cattle for Western Range Environments. (2nd Edition) WCC-1 #TB-99-1. The Samuel Roberts Noble Foundation, Ardmore, OK.

Lasley, J.F. (1978) Genetics of Livestock Improvement. Prentice-Hall.

National Beef Cattle Evaluation Consortium. Retrieved from http://www.nbcec.org/.

Dolezal, S.L., and D.S. Buchanan (1993) Expected Progeny Difference: Part I. Background on Breeding Value Estimation. OSU Extension Facts F-3159, Cooperative Extension Service, Oklahoma State University.

Dolezal, S.L., and D.S. Buchanan (1993) Expected Progeny Difference: Part II. Growth Trait EPDs. OSU Extension Facts F-3160, Cooperative Extension Service, Oklahoma State University.

Dolezal, S.L., and D.S Buchanan. (1993) Expected Progeny Difference: Part III. Maternal Trait EPDs. OSU Extension Facts F-3161, Cooperative Extension Service, Oklahoma State University.

Dolezal, S.L., and D.S. Buchanan (1993) Expected Progeny Difference: Part IV. Use of EPDs. OSU

Extension Facts F-3162, Cooperative Extension Service, Oklahoma State University.

Dolezal, S.L., D.S. Buchanan, and A.C Clutter. (1995) Inbreeding in Cattle. OSU Extension Facts F-3165, Cooperative Extension Service, Oklahoma State University.

Oklahoma State University Breeds of Livestock. Retrieved from http://www.ansi.okstate.edu/bre eds.

Rich, T.D., and R.R. Frahm (1977) Systems of Crossbreeding. OSU Extension Facts F-3151, Cooperative Extension Service, Oklahoma State University.

Society for Theriogenology / American College of Theriogenologists. Guidelines for The Bull Breeding Soundness Evaluation.

Taylor, R.E. (1994) Beef Production and Management Decisions. (2nd Edition). MacMillan Pulbishing Co. New York.

VanVleck, L.D., and L.V. Cundiff. Across-Breed EPD Tables for the Year 2003 Adjusted to Breed Differences for Birth Year of 2001. Proceedings: Beef Improvement Federation Research Symposium and Annual Meeting, Lexington, KY. May, 2003. Pg. 55-63.

i The following discussion is adapted from D.S. Buchanan and E.D. Tinker. 1989. Current genetic predicition systems for beef cattle. Proc. KOMA Beef Cattle Conference. Updates were made using the 2002 Beef Improvement Federation Guidelines and Understanding Animal Breeding–2nd Edition (2000) by R.M. Bourdon.

http://www.nbcec.org/

http://www.ansi.okstate.edu/breeds

chapter 20. beef cattle breeding

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