13 spec lines for beef breeding - university of arizona · breeder. the first calves were dropped...

Genetics and Reproduction 1993 1

SPECIALIZED LINES FORBEEF BREEDING HERDS

D.E. Ray, 1 A.M. Lane,2 and

C.B. Roubicek3

UA RESEARCH

Research conducted by The Universityof Arizona Animal Sciences Depart-ment indicates that the use of special-ized sire and dam lines could improveproductivity of commercial beef breed-ing herds.

This conclusion is based on an experi-ment which compared the breedingperformance of topcross progeny ofthree inbred sire lines with each otherand with an outbred control herd.Comparisons involved birth weights,weaning weights, and weaning confor-mation and condition scores of 400 bulland heifer calves. The cattle were fromthe registered Hereford herd owned bythe San Carlos Apache Indian Tribe.The herd is maintained approximately60 miles east of Globe, Arizona, on asemi-arid range at an elevation ofapproximately 5,000 feet. The breed-ing season normally extends from May1 to August 1, and calves are weanedand evaluated in October or earlyNovember. No supplement wasprovided for cows and calves during theperiod of this study.

The topcross parental stock involved inthis study were the progeny of eightsires from three inbred lines (1, 6 and9) of the U.S. Range Livestock Experi-ment Station, Miles City, Montana.

Since some of these lines have be-come very popular in the beef industry,a brief history of their development ispresented.

Of the original sires (grand-sires of thecalves included in this study), four werefrom line 1 and two each from lines 6and 9. Parents designated SC (SanCarlos) were the progeny of 30 pure-bred sires originating within the herd.With the exception of the controlmatings (SC X SC), the parental stockwas composed of 50% SC breedingand 50% of the respective line involvedin the topcross mating. Topcross sires

Line 1 cows traced back to stock purchased in1926 from George M. Miles of Miles City,Montana. Most of the foundation cowswere sired by Colonel Perfection and histwo sons, Colonel Grayfield 2nd and Colo-nel Defender 3rd, and two other bulls,Domino Perfection 3rd and Blanchard 40th.These cows were mated to two half broth-ers, Advance Domino 20th and AdvanceDomino 54th, purchased from a Coloradobreeder. The first calves were dropped in1934, and the line has remained closed tooutside breeding since that time.

Line 6 was initiated in 1948 with the purchase of30 heifers and two bulls of Real PrinceDomino breeding from a Nebraska breeder.The foundation sires were Perfect Lad18th and Maude’s Mischief 19th. The firstcalves were dropped in 1949.

Line 9 resulted from twenty-eight head of heifercalves and one bull calf of King Dominobreeding purchased from a Montanabreeder in 1948. The foundation sire ofthis polled line was Seth Domino. The firstcalves were dropped in 1951.


topcross bulls on San Carlos cows)resulted in calves that were among thelightest (469 lbs.). A difference of thismagnitude (45 lbs.) has some importantimplications. First of all, it indicates thatfactors associated with the cow (mater-nal ability) are more important underArizona range conditions than thegenetic potential of the calf in determin-ing growth of the calf to weaning. Thisprobably reflects differences in themilking ability of the cow. Secondly, itsuggests that there may actually be anantagonism between preweaninggrowth and maternal ability. Additionalevidence for this antagonism is seen inthe results of crosses involving line 1.Although the differences between thereciprocal crosses is not as great in thiscase (16 lbs.), it is still large enough tobe of economic importance.

Conformation andcondition scores are alsolisted in the table. Ingeneral, the resultsfollowed the same trendsas noted for weaningweight. Higher scoreswere observed whenthese inbred lines wereused in the cow side ofthe cross. All of thevalues would be consid-ered very acceptable forHereford calves atweaning.

These results indicatethat two (1 and 6) of thethree inbred lines testedwere much more valu-able when incorporatedinto cows than in bulls.This would mean thatdifferent criteria forselection of bull andheifer calves at weaningwould be the most

efficient system. A natural outgrowth ofthis procedure would be a breedingprogram using specialized sire anddam lines for commercial beef produc-tion.

Table 1. Birth and Weaning Traits by Line of Breeding

were chosen from those available to beas representative of the group aspossible. The number of sires usedwere:

Ll X SC-2 L9 X SC-2

L6 X SC-2 SC X SC-3

Results from the experiment arepresented in Table 1. Birth weights ofthe calves averaged 74 lbs., with minordifferences among the various breedinggroups. Heaviest calves at birthincluded line 9 cross cows mated toSan Carlos bulls, whereas the lightestcalves were from San Carlos cowsmated to topcross line 9 bulls.

Substantial differences occurred inweaning weights. The heaviest calveswere produced by topcross line 6 cowsmated to San Carlos bulls (514 lbs.).Surprisingly, the reciprocal cross (line 6

Sire Dam Birth Weaning Conformation ConditionLine Line Weight Weight Scorea Scorea

(lbs.) (lbs.)

1 X SC 74 476 11.1 10.5

6 X SC 76 469 11.1 10.5

9 X SC 73 470 11.1 10.8

SC 1 76 492 11.5 11.1

SC X 6 74 514 11.8 11.1

SC X 9 76 466 11.3 10.9

SC X SC 75 479 11.4 10.8

Average 74 479 11.3 10.8

a Evaluated on a 15 point scale, with higher values indicating more desirable conformation or greater condition. A condition score of 11-12 is considered optimum.

X


Department of Animal ScienceLivestock SpecialistCollege of AgricultureThe University of ArizonaTucson, Arizona 85721

One of the more effective methods ofdeveloping specialized lines is throughcrossbreeding. Breeds of cattle oftenexcel in different desirable traits.These same traits are present withindifferent lines of the same breed ofcattle, but the differences are normallynot as great as between breeds andthus are more difficult to identify.Desired traits for brood cows are earlypuberty, high fertility, ease of calving,adequate milk production, adaptability,a strong mothering instinct, etc.Oftentimes large mature size or weightis a disadvantage in the cow herd,especially on southwest ranges. Thebull’s major contribution is in size andweight as reflected by growth rate of hiscalves. Other traits are also important,such as the ability to travel, libido (sexdrive), desirable muscling, relativelysmall calves at birth, etc.

One example of such a crossbreedingprogram is the “terminal sire” system.All of the cows are crossbreeds devel-oped from two (or more) breedsselected specifically for maternalcharacteristics and adaptability. Bullsare selected from a breed differing fromthose in the cow herd with primaryemphasis on growth and carcasscharacteristics. All calves produced goto market, hence the term “terminalsire.” Research results indicate anincrease of approximately 25% inpounds of calf weaned per cow withthis system.

The use of specialized sire and dam“lines,” either within a breed or throughthe use of different breeds, provides thebreeder with a technique to substan-tially improve production.

2 (Retired)1, 3 (Deceased)


FROM:

Arizona Ranchers' Management GuideRussell Gum, George Ruyle, and Richard Rice, Editors.Arizona Cooperative Extension

Disclaimer

Neither the issuing individual, originating unit, Arizona Cooperative Extension, nor the Arizona Board ofRegents warrant or guarantee the use or results of this publication issued by Arizona CooperativeExtension and its cooperating Departments and Offices.

Any products, services, or organizations that are mentioned, shown, or indirectly implied in thispublication do not imply endorsement by The University of Arizona.

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation withthe U.S. Department of Agriculture, James Christenson, Director, Cooperative Extension, College ofAgriculture, The University of Arizona.

The University of Arizona College of Agriculture is an Equal Opportunity employer authorized to provideresearch, educational information and other services only to individuals and institutions that functionwithout regard to sex, race, religion, color, national origin, age, Vietnam Era Veteran’s status, orhandicapping conditions.


BULL SELECTION

Richard W. Rice1

One of the most important decisionsthat a cattle producer makes is theselection of bulls for his cow herd.Bulls contribute half of the geneticmaterial for the cow herd. If replace-ment heifers are selected from withinthe herd, the bull will influence theproduction of the herd for up to 10years or more.

BASIS FOR BULL SELECTION

Bulls are selected for their geneticpotential. It is difficult to determinegenetic values of bulls since theoutward appearance (phenotype) are aresult of both genetic potential and theconditions under which the animal wasdeveloped (environment). Nutrition,climate, diseases, parasites and insectsplus weather conditions influence theoutward appearance of the bull. Wherepossible the animal should be com-pared with other animals within thesame herd and should be raised underconditions similar to those which he isexpected to perform. However, thegenetic value of bulls can be deter-mined and compared with bullsthroughout the country because of thesire record systems of the purebredbeef cattle associations.

INDIVIDUAL EVALUATION

The genetic value of a bull can beestimated by his own performance. Inaddition, the physical attributes heexpresses visually will aid in selection.Genetic values are often available thattake into account the performance ofhis sire, dam, grandsire, granddam,herdmates and brothers and sisters.The genetic evaluation is called Ex-pected Progeny Differences (EPD).

For Bull Selection, a breeder shouldestablish goals for his own herd,evaluate herd strengths and weak-nesses and select bulls which willimprove the production and geneticmerit of the herd. Selection has toinclude a realistic appraisal of theresources available to support the cowherd and growth of calves.

There are three major categories ofbulls needed for commercial beefproduction.

One or all of these categories may beuseful in a breeding program basedupon the goals of the manager and thequality and quantity of feed resourcesprovided by the ranch.

EDP values may be used to achievedesired production goals. However,EPD’s for many desirable traits are notavailable. A listing of important traitsfor which information may be availableis given in Table 1.

1. Maternal bulls for use on heifers.

2. Maternal bulls for use on cows.

3. Terminal bulls for use on cows.


Trait Maternal Bulls Terminal BullsFor Heifers For Cows For Cows

Scrotal Circumference Large Large Medium-Large

Pelvic Area Large Large Not Important

Calving Ease High High High

Birth Weight Low Medium Medium

Weaning Weight Match Match High

Milk Match Match Not Important

Total Maternal Match Match Not Important

Yearling Weight Match Match High

Carcass Percent Protein Conflict Conflict High

Carcass Quality High High High

Table 1. Traits for Selection of Bulls Based Upon Function

Where match is listed, the bulls selectedshould be matched with the resourcesavailable on the ranch. Matching isillustrated in Table 2.

Mature Size Milk Level Availability of Food from Grazing

Low Medium High

L H - 0 +

L M - + +

L L 0 + +

M H - - +

M M - 0 +

M L - + +

H H - - 0

H M - - 0

H L - 0 +

+ = Matching mature size and milk production with resources. 0 = Risky, extra feed may be necessary or fertility and production may

be affected. - = Avoid the combination, production will be unsatisfactory.

Table 2. Matching Bulls to the Resources

High levels of milk produc-tion require more feedresources. An increase of5 lb. in milk productionincreases energy requiredby 15%, protein requiredby 21% and minerals(calcium and phosphorus)by as much as 37%.

Larger cattle require morefeed. An increase inmature cow size from 1000to 1200 lb. results in a 15-20% increase in themaintenance requirement.

Most of the genetic traitsavailable from performancerecords and EPD’s arebased upon increases inthe weight and growth of

cattle. If we all select for size in-creases, the result may be a mis-matchof resources to support the herd, loss ofmaternal factors affecting fertility and areduction in the efficiency of production.Excessive size is not desired by themeat industry, therefore, requirements

for the final product must be involvedin selection.

Size affects weight required forpuberty, successful reproduc-tion and desirability of the finalproduct. For example, a 1400lb. cow will produce heifers thatwill not reach puberty until theyweigh 900 and steers that willnot grade choice until theyreach a weight of 1300 lb.

Heifer development and fertilityare important and resourcesnormally available will notproduce the desired puberty oflarge animals at a young age.Cattle feeders, packers andretailers do not desire exces-sively heavy cattle. Therefore,sire selection has to bematched with the resourcesavailable, maternal efficiency of


heifers produced and the productdesirable to feeders, packers, retailersand consumers.

Breeding systems to achieve productiv-ity, fertility and a desirable final productcan be classified into three systems.

1. All purpose:

Cow size and milk production arematched with feed resources and bulls ofthe same biological type are selected.Replacement will have similar desiredattributes as the cow herd.

2. Combination:

Cow herd size and milk productionmatched to the feed resources. Replace-ments are produced by mating bulls withmaternal desirability with heifers andyoung cows.

Mature cows, 4 years old or older, aremated to terminal sires, all calves aresold.

3. Terminal Sire System:

Matched cows are mated to large bulls.All calves are sold. Replacements arepurchased or bred separately.

Department of Animal Science 1

College of Agriculture

The University of Arizona

Tucson, Arizona 85721

REFERENCES

Brinks, J.S., 1990. Cattleman’s Hand-book for Expected Progeny Differ-ences. J.S. Brinks, P.O. Box 710,LaPonte, CO 80535.


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Disclaimer






RANGE BEEF HERD

GROWTH SELECTION

D.E. Ray,1 A.M. Lane,2

C.B. Roubicek,3 and R.W. Rice4

A major economic goal of the cattleproducer and others in the beef indus-try is the genetic improvement ofgrowth traits in range cattle. Superiorgenetic growth potential is reflected inimproved feedlot efficiency and carcassdesirability. These factors make itimperative that the cattle producer useaccurate objective measurements andselection methods to identify thesuperior genotypes in his herd.

The growth performance of range beefcattle in areas of year-long grazingreflects forage availability as well asclimatic stress conditions. Becauseannual rainfall and temperature pat-terns in an area directly influencequantity and quality of range forage, allrange stock are subjected to varyingperiods of feed or nutrient restriction.Live weight and body measurementdata show that with only range feedavailable, growth in weight is strictlyseasonal from weaning to maturity.

A successful selection program forimprovement of performance traits inbeef cattle depends on selection for aspecific trait and understanding howselection for one trait may influenceother traits. The major purpose of thestudy to be described was to obtaininformation on genetic parameters ofgrowth of range beef cattle under apractical management system. Thisinformation should be directly appli-cable to a performance testing programfor the range cattle producer.

MATERIALS AND METHODS

Data were obtained from the registeredHereford herd owned and maintainedby the Apache Indian Tribe at SanCarlos, Arizona. With the initiation ofthe study, individual breeding pastureswere developed for the registered herd.Each pasture carries 30 to 35 cowsand averages about 600 acres in size.Cows were allotted to the breedingpastures in January for calving duringthe following three months and re-mained in the individual pasturesthrough the breeding periods, May 1 toJuly 30.

The general range area is at an altitudeof 5,000 feet, with range forage con-sisting primarily of desert grasslandvegetation. Annual rainfall averagesabout 14 inches with most of it occur-ring during the summer months of Julyand August. Temperatures may rangefrom -20°F in January to 95°F in July.

Individual data recorded at birthincluded identification, birth date andweight. The calves were ear tattooedwith individual identification numbers.During the nursing period pertinentcomments concerning unusual mater-nal or calf information that could affectperformance were noted.

In the fall all cows and calves werebrought to corrals for weaning. Thecalves were weighed and individuallyscored by three judges for conforma-tion and condition.

Bulls and heifers were maintainedseparately after weaning. Subsequentweights and scores were obtained inthe early spring (about March 1) beforethe appearance of new range forage,again in the fall at weaning time andthe following spring. Thus, four stagesof development were represented, withan average mean age at each stage of8, 11, 20 and 23 months. Recordsfrom more than 1,500 calves wereutilized in this 10-year study.


None of the bull calves were castratedduring this period. The herd wasmaintained on a year-long grazingprogram with little, if any, supplementa-tion. It should be noted that during themore severe winters of the test periodsnow cover remained on the ground forseveral days at a time.

Sires used in the herd during the yearsof this study came from many differentsources. They included purebred herdsfrom Arizona and surrounding states,the Arizona Agricultural ExperimentStation, United States Department ofAgriculture performance tested lines,and bull progeny produced in the herd.

RESULTS

Average weights and the heritabilitiesof the weight at each age are summa-rized in Table 1. Only the bull calvesare included in this report, althoughsimilar results were obtained withheifers. The average weaning weightof 480 lbs. at an average age of eightmonths translates into a daily gain frombirth to weaning of 1.7 lb. This empha-sizes the importance of having cowscalve early in the season, as onemonth’s difference in birth date resultedin an average difference of 50 lb. forthe calf at weaning.

The weight losses that occurred overthe two winter periods (weaning to 11months and 20 to 23 months of age)should be very typical ofunsupplemented range cattle in Arizona

Table 1. Average Weights and Heritabilities

Weight HeritabilityAge (lbs.) Percent

Birth 76 50Weaning 480 15340 days 440 30600 days 825 50710 days 700 50

and many other parts of the world. It isnot uncommon for animals to lose 10%or more of their weight from fall tospring under these conditions.

The highest values for heritability (50%)were for birth weight, long yearlingweight (20 months) and weight ascoming two-year olds.

The lowest heritability was for weaningweight (15%), with short yearling weighthaving a heritability of 30%. Manytimes the meaning of heritability ismisunderstood. Probably one of thebest ways to use a heritability value isin predicting how much improvementcan be made when selecting for aparticular trait. As an example, assumewe selected replacement bulls andheifers in this herd that averaged 50 lb.above the weaning weight for the herd.We call this value (50 lb.) the selectiondifferential. If we mate these replace-ments together, then we would expecttheir calves to have an average wean-ing weight 15% (heritability) of theselection differential (50 lbs.) above theherd average (480 lb.). In this case,that would be 15% x 50 lb. + 480 =487.5 lbs. Obviously, the higher theheritability value for a trait, the moreimprovement we will make in theprocess of selection.

The major questions posed in this studywere (1) what effect does selection fora specific trait have on other traits, and(2) when would be the “best” time toselect replacement animals. To helpunderstand Table 2, let’s consider theinformation on the first line. In thiscase, we are selecting only for heavierbirth weights (which we probably wouldnot do). If this were the actual situa-tion, birth weight would be increased by5 lb. per generation. Due to what wecall the correlated response, the otherweights would also increase. In thisexample, selection for birth weightwould also result in weaning weightincreasing by 4 lb., yearling weight by 5lb., and 20 and 23 month weights by 10lb. each.


Research ScientistExtension SpecialistResearch Scientist (Deceased)Professor, Department of Animal SciencesCooperative ExtensionCollege of AgricultureThe University of ArizonaTucson, Arizona 85721

selecting for this weight is a greaterincrease in birth weight than we wouldexpect by selecting at weaning time.To overcome this problem, we coulduse an index which selects againstheavier birth weights and at the sametime selects for heavy long-yearlingweights. One index that has beensuggested is 1 = Y - 3.2B, when 1 =index value, Y = yearling weight, and B= birth weight. As compared to selec-tion on yearling weight alone, this indexwould reduce the expected increase inbirth weight by 55% while reducing theimprovement in yearling weight by only10%. Thus, near maximum improve-ment can be made in growth rate whileminimizing the usually undesirableincrease in birth weight.

Table 2. Direct and Correlated Response to Selection

TraitSelected 11 20 23For Birth Weaning months months months

Birth weight 5 4 5 10 10Weaning weight 1 6 7 9 811 month weight 1 7 12 13 1520 month weight 2 7 11 25 2223 month weight 2 6 12 22 25

Change in Weight (lb.) At:

If we are primarily concerned withweaning weight, we would expect toimprove it by 6 lb. per generation if weselected directly for it. However, wecan make just as much (or more)improvement in weaning weight if weselect for weights measured later in life.This may not seem reasonable, but it isdue to three factors: 1) the heritability ofweaning weight is low; 2) the heritabilityof yearling or two-year old weights ishigher; and 3) the correlation betweenthe latter traits and weaning weight ishigh. The weight taken at long-yearlingage (20 months) appears to be “best”when we consider both preweaning andpost-weaning gain performance, as it isthe youngest age which results in anear-maximum improvement of alltraits. One possible disadvantage of

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1

3

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ESTRUS SYNCHRONIZA-TION AND ARTIFICIALINSEMINATION FOR

BREEDING BEEF CATTLE

R. Rice1

Artificial insemination of cattle hasproven to be very effective for theimprovement of the genetic potential forproduction. In dairy production, over80% of all cattle are now bred artifi-cially. The success of dairy producersin improving milk production has beenimpressive. A large proportion of thesuccess is due to improvement of thegenetic potential of dairy cattle throughuse of outstanding sires by artificialinsemination.

Artificial insemination in beef cattle hashad limited use. The managementnecessary for success has limited itsapplication primarily to seed stockproducers. One of the main barriers touse in commercial beef cattle opera-tions is the time and labor necessaryfor detection of estrus (heat) andinsemination at the proper time duringheat.

This barrier has been effectivelyremoved with the availability of meth-ods to synchronize heat. With estrussynchronization groups of cattle can beinduced into fertile heat and bred at aspecified time following initiation of theheat period. The success of thisprogram is based upon a total manage-ment program. Synchronization willnot improve cattle fertility. In fact, itis difficult to achieve fertility levelssimilar to those resulting from naturalmating. For success, a total fertilitymanagement program is necessary.

KEY ELEMENTS OF FERTILITY MANAGEMENT

There are three groups of animalswhich need to be considered sepa-rately:

1. Replacement heifers2. Young cows with their first calf3. Mature cows, having 2 or more

calves

Replacement Heifers

If the goal is to breed the replacementheifers at 12-14 months of age, aspecial heifer development program isessential. Some general rules apply:

1. They must be at least 12months old or preferably olderat breeding.

2. They must weigh at least 650lb at breeding.

3. They must have a bodycondition of 5 or higher atbreeding.

When replacement heifers are se-lected, usually in the fall, plans for thedevelopment program must be made.

1. Evaluation of heifers in the fall:

An estimate of the age, weightand condition of the heifers isrequired so that the heiferdevelopment plan can bemade.

For example: Fora heifer, born inMarch/April andweaned on orabout 1 October,the followingcalculationsshould be made:

Nutrition required to achievetarget weight:

Weaning weight 500 lb

Age at weaning 6 months

Target weight breeding season 650 lb

Gain necessary to meet target wt. 150 lb

Breeding date desired 1 May

Days weaning to breeding 211 da

Average daily gain to breeding 0.75 lb/day


Generally the nutrients which aremost likely to be required forgrowth and development areprotein, energy and phosphorus.

Requirements for the desired gain are:

In alfalfa hay equivalents the heiferswould require:

The heifers would have to eat 19 lbalfalfa hay daily to meet energy (TDN)requirements. At the weight and age ofour example, they would not likely eat 19lb. Therefore, to ensure desired perfor-mance, a better energy source would benecessary.

For our calculations, we will feed anaverage of 9 lb alfalfa hay daily andchoose a good energy source for the restof the ration:

For example:1. Corn at 80% TDN to supply required energy:

TDN required 10.0TDN from hay 9 lb x .52 = 4.7

TDN needed from corn 5.3Lb corn = 5.3/0.80 = 6.6 lb corn daily

Ration for heifers:

9 lb alfalfa hay6.6 lb corn15.6 lb Total

2. Whole cottonseed at 90% TDN to supply energy:

5.3 lb TDN required/.90 TDN cottonseed = 6 lb cottonseed dailyRation for heifers:

9 lb alfalfa hay6 lb cottonseed15 lb daily ration

Heifers, pregnant with first calf in the fall.

Evaluate weight and condition of heifersin the fall. Condition is the most impor-tant indicator of management needsprior to calving and rebreeding forsecond calf:

In fall, condition of these heifersshould be at least 5-6. Duringwinter, without extra feed, exceptrange forage, they would be ex-pected to lose weight and at leastone condition score. If the conditionscore at breeding in the spring is 4or less, the fertility in the breedingseason will be lowered. At fallevaluation, you can anticipatewhether or not supplements may berequired during late pregnancy andinto the breeding season for thisgroup. If fall condition appears tobe marginal, supplements begun 1month prior to calving and intogreen feed following calving shouldbe planned.

It takes about 80 lb gain in weight toimprove 1 condition score. Cattle willnot usually gain weight during the winterand most likely will lose weight on rangeforage. Heifers should be handledseparately, if possible, and wintered onthe best winter range. A secondcondition evaluation about 1 month priorto calving should be made and supple-

Protein lb/day 1.5

Energy lb TDN daily 10.0

Phosphorus Daily 14.0g .03lb .5 oz

Alfalfa hay 16% protein, 52% TDN, .25%P

For protein requirement 9.4 lb daily

For TDN requirement 19.2 lb daily

For phosphorus requirement 12.0 lb daily


ments of PEP planned if needed. If again of 80 lb is needed (1 conditionscore) two months prior to the breedingseason, the animals would have to befed to gain 1.3 lb per head daily. Forthis gain the requirements are asfollows:

It would require about 20-25 lbs alfalfahay daily which could be provided andeaten. However, a combination of hayplus an energy source could be supe-rior.

The ration to be fed approximately 1month prior to calving up to greenup.

Much less feed would be required if thecows were condition score 4 or higherjust prior to calving. Ideally conditionwould hold up from the fall without morethan a supplement containing PEP fedat 3-4 lb/head daily, 1 month prior tocalving and up to greenup.

Last 1/2 Pregancy Lactation/Breeding

Protein (lb/day) 1.7 2.0TDN (lb/day) 10.0 12.0

Phosphorus (g/day) 19/0 25.0

Again, alfalfa hay required lb/day

Protein 10 12.5TDN 18 22

Phosphorus 16 24

TDN required 12TDN from alfalfa _5.5

TDN from energy source 6.5 lb

With corn 6.5/.82 = 8 lb corn daily

Ration: 10 lb alfalfa hay

8 lb corn

With cottonseed

6.5/.9 = 7 lb cottonseed daily

Ration: 10 lb alfalfa hay 7 lb cottonseed

For example: Feed 10 lb alfalfa daily

Mature cows, age 2 or more in the fall.

Fall condition score should be 5 orgreater.

Generally extendedfeeding of the cowherd should not benecessary except forunusual years wheresummer/fall rangegrowth and quality islimited by drought. Anevaluation of thecondition of the cowsand of the quantity offorage available in thefall should help you to

anticipate potential fertility problemsthe next spring. A minimum supple-ment of 1-2 lb. daily may be required ifthe range is primarily grass. Supple-ments should be fed based upon cowcondition and nutrient content of therange forage.

Generally: cows will notgain weight or condition inthe winter. Therefore, fallcondition evaluation willidentify potential problemsand culling/supplementa-tion decisions madeaccordingly.

Livestock Specialist 1

Cooperative ExtensionDepartment of Animal SciencesCollege of AgricultureThe University of ArizonaTucson, Arizona 85721


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Disclaimer



Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperationwith the U.S. Department of Agriculture, James Christenson, Director, Cooperative Extension, College ofAgriculture, The University of Arizona.



the above example is 5%, using theformulas below from the 1988 publica-tion Crossbreeding Beef Cattle forWestern Range Environments TB-88-1(Kress and Nelson, 1988).

Amount of heterosis =

AH + HA - A + H 2 2

or445 lbs. - 425 lbs. = 20 lbs.

Percent of heterosis =

amount of heterosis • 100 A + H 2or

20 • 100 = 5% 425

As Kress and Nelson mention, “hetero-sis can be positive or negative andthere can be positive heterosis evenwhen one of the parental breedsperforms better than the average ofcrossbreds.”

MATCHING THE ENVIRONMENT

There are three major areas in whichone would wish to utilize heterosis:maternal traits, growth traits, andcarcass traits. Maternal traits are thosewhich relate to milking ability, concep-tion, and mothering ability. Growth traitsinclude average daily gain, which inturn influences yearling weight. Car-cass traits are related to lean productyield and quality grade. Commercialcattle ranchers commonly seek maternalheterosis by using the crossbred cowwith her increase in total lifetimeproduction. As mentioned above,carcass heterosis is not large (0 to 5%),but is commonly practiced by utilizinglean muscle breeds such as Limousinand Charolais in terminal sire breedingprograms. These fast growing, heavilymuscled sires are used with smalleradapted females that are 4 years old orolder and all offspring are sold. Also,carcass heterosis is sometimes sought

INTRODUCTION

Thirty years ago, price discounts wereapplied to ranchers’ calves resultingfrom crossbreeding. Beginning in the1970s, crossbreeding became popularwith many different breeds beingimported into the United States over thenext fifteen years. Research and ranchrecords have shown an increase inproduction through the use of cross-bred cows. The use of crossbred cowshas been shown to increase overalllifetime production by 25%. At ClayCenter, Nebraska, 50% of crossbredcows have been shown to be still inproduction at age 7. Clay Center alsoreported that the crossbred cow staysin the herd 1.3 years longer than thestraightbred cow.

The establishment of any new breed oflivestock is always accompanied by acertain amount of inbreeding depres-sion which reduces conception andsurvival. Properly managed (no largebreed sires on small framed, youngcattle), crossbreeding restores to cattlepopulations some of the fitness whichwas lost during breed development.The largest advantage seen withcrossbreeding is with less heritabletraits such as reproduction and cowlongevity. Little advantage will be seenwith highly heritable carcass traits. Theadvantage expressed by crossbredcattle over the average of both parentsis referred to as hybrid vigor or heterosis.For example, assume Hereford (H)calves weigh 450 lbs. at weaning andAngus (A) calves weigh 400 lbs. TheF1 cross calves weigh 440 lbs. forAngus x Hereford (AH) and 450 lbs. forHereford x Angus (HA). Heterosis for

CROSSBREEDINGSYSTEMS FOR ARIZONA

RANGELANDS

Jim Sprinkle1


by breeding a cow herd with less abilityto have intramuscular marbling (suchas high percentage of Brahman orcontinental breeding) to sires known tohave the ability to deposit marbling(such as British breeds like Angus).The practice of combining the strengthsand weaknesses of different breeds tomeet marketing goals or to bettermatch a harsh range environment iscalled complementarity.

It must also be remembered thatdesirable genetic traits are oftencorrelated with other less desirabletraits. For example, accelerated aver-age daily gain and increased carcassyield are usually correlated with largebirth weights.

It is possible to exceed the rangeenvironment available to the cowherdwhen designing crossbreeding sys-tems. For example, milk production canbecome excessive for the amount offeed produced by most rangeland (lessthan 20 inches rainfall). Milk productionfor most beef breeds peaks at 60 to 70days at around 18 to 20 lbs. per day.Heavier milking, dual-purpose breedcrosses have peak lactations of 22 to26 lbs. per day. Each additional lb. ofmilk production requires approximately.52 lbs. of additional forage intake eachday. Another example of exceeding arange environment is by utilizing largebreeds in the development of thecrossbred cow for an arid environment.An environment characterized byabundant, high quality summer forageand ample winter feed resources canuse a large frame size, heavy-milkingcrossbred cow. Most western range-land requires the use of intermediate orsmall framed cattle with moderate milkproduction. As winter feed resources oravailable forage for grazing decrease,cow size and milk production need todecrease also. At Havre, Montana inthe Bear Paw Mountains (20 in. annualprecipitation) Simmental x Herefordcows had superior weaning weight/cowexposed averages when compared toAngus x Hereford cows. When the

Table 1. Breed Comparisons in the Germplasm Evalua-tion Program at Meat Animal Research Center (MARC)

aIncreasing number of Xs indicate relatively higher values. For example,XXXXXX is greatest milk production or oldest age at puberty and X is lowestgrowth rate and youngest age at puberty. © Copyright 1996, Roman L.Hruska, U.S. Meat Animal Research Center–USDA, Clay Center, Nebraska.Available at http://www.ansi.okstate.edu/breeds/research/table2.htm.

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)hS(nrohtrohS XXX XX XXX XXX

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)M(uojnAeniaM XXXXX XXXX XXX XXX

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)L(nisuomiL XXX XXXXX XXXX X

)C(sialorahC XXXXX XXXXX XXXX X

)iC(aninaihC XXXXX XXXXX XXXX X


same type of cows were compared atMiles City, Montana (10 to 12 in. annualprecipitation), Angus x Hereford cattleexcelled in calf weaning weight/cowexposed.

DESIGNINGA CROSSBREEDING SYSTEM

Unlike the dairy industry, there is noparticular breed which excels in beefproduction in the United States. Varia-tion among environments requires theuse of different breed combinations. Inthe Gulf Coast region, use of a heattolerant breed is needed, while NorthDakota would require the opposite.Ranchers should outline productiongoals for the ranch and then look atpossible biological types of cattle tohelp achieve those goals. Limitationswhich may influence the success ofusing different biological types of cattleor different crossbreeding systemsshould also be considered. Possiblelimitations include feed and forageresources, labor, rainfall, ability tosupplement cattle, number of pastures,size of the herd, herd replacementstrategy, temperament desired,adequacy of corral facilities, andcommitment to management.

Tables 1 and 2 categorize differentbiological types of cattle and cross-breeding systems, respectively. InTable 1, cattle are separated into fourmajor traits by biological type. Sometraits desired will conflict with produc-tion goals. For example, if retainingoffspring to slaughter, increased lean tofat ratio may be important. However, forrange cows it is particularly importantfor cows to have the ability to store fatduring times of nutritional plenty so theycan use it during nutritional deprivation(less lean to fat ratio). If you would liketo use a breed in your environment thathas a particular trait you would like tobe present in the herd (e.g., increasedgrowth rate) but that may also conflictwith environment adaptability (e.g.,mature size), limit that particular breedto 25% or less of the crossbred cow or

consider using the breed as a terminalsire.

For Table 1, much of Arizona can becharacterized by these generalassumptions:

1. Keep milk production for replace-ments at XX or XXX (Table 1).

2. Keep age at puberty at XX or XXX.

3. For the cow herd, keep lean to fatratio (ability to store fat) at XX or XXX.For terminal sires, it doesn’t matter.

4. For mature size, keep the cow herdat XX or XXX. For terminal sires, usecommon sense when combiningdifferent breeds (i.e., don’t use aXXXXX sire on X or XX mature sizecows due to calving problems).

5. For conflicting traits, lean towardscow herd adaptability by following the25% or terminal sire rule above.

Once biological types are identified fordeveloping a crossbred system (Table 1),constraints may be necessary toachieve uniformity among calves(Table 2). For example, rotational orcomposite crossbreeding systemsrequire the use of similar biologicaltypes to prevent excessive variationamong cow generations due to generecombination. An extreme examplewould be a rotational cross breedingsystem utilizing one breed with 2 Xsfor growth and another breed with 5 Xsfor growth. Cow size and necessarynutritional management would fluctuatewildly from one generation to another,depending upon the current sire beingused. If the rancher were to purchasereplacement females each year (suchas Braford F1 cattle for use in SouthTexas), fluctuation problems could beavoided. Another constraint inherentwith crossbreeding systems is addi-tional management requirements.Cattle have to be separated andmaintained by breed or age duringbreeding for rotational and terminal sire


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Table 2. Resource Constraints and Advantages and Disadvantages of Different Breeding Systems

Heterosis is in weaning weight/cow exposed.Adapted from: Crossbreeding Beef Cattle for Western Range Environments TB-88-1, 1988, D.D. Kress and T.C. Nelson, NVAgricultural Expt. Sta., University of NV-Reno and Table 2, “Make Crossbreeding Work on Your Place,” Part 1, Michael MacNeil,3/2/96, Western Beef Producer.


breeding systems, respectively. Thisrequires the use of additional breedingpastures (Table 2), which may bedifficult for some public lands grazingallotments. Alternative crossbreedingsystems for smaller herds or those withfewer management capabilities are theperiodic rotation or composite systems.When using simplified crossbreedingsystems, it is still important to carefullyplan which biological types will be usedto achieve production goals. Haphazardbreeding programs lead to haphazardresults.

EXAMPLE CROSSBREEDINGSYSTEM

Note: This example is for discussiononly to show how a rancher mightdesign a crossbreeding system to fit hisparticular ranch and production goals. Itis not meant to be a blueprint for allranches in Arizona!

John Smith of the Lazy Upside Down Udesires to initiate a crossbreedingsystem to reap the benefits of bothindividual (crossbred calves) andmaternal (crossbred cows) heterosis.He has a herd consisting of 200straightbred Hereford cows which grazea USFS allotment (elevation 6200 to7500 ft.) from June 1 to October 15.From October 15 to May 31, cattlegraze BLM or Arizona State Land Dept.pasture (elevation 2700 to 5000 ft.).Calving season is from March 1 to May15 (unassisted) and bulls run with cowson the USFS permit from June 1 toAugust 15 at a 1:33 bull:cow ratio. Thecurrent allotment management plan onthe USFS allotment allows for the cowherd to be split into two herds. Cattleare supplemented with protein once aweek (14 lbs. cottonseed meal cake percow) for January and February only. Allcalves are weaned on the mountainand sold at weaning except for 40replacement heifers, of which 20 to 30will be retained and the remainder soldas yearlings. John’s family desires toincrease weaning rate while maintainingweaning weights. Although weaning

weights have been adequate (403 lbs.for heifers, 458 lbs. for steers), Johnand his family have had problemsmaintaining cow body condition duringthe winter without supplementationduring January and February. Calvingrate is around 80% and weaning rate is75%. Mature cows weigh 1100 lbs. andreplacement heifers calve at 2 years ofage. Everyone agrees that while thenutritional quality of the forage availableis generally excellent on the mountain,the forage quality of the winter forage islimiting (when tested over 2 years, hairygrama was 5.5% crude protein and48% TDN). The family desires to limitsupplementation to the current timeperiod. The Smiths have 40 acresprivate ground of which 12 acres areirrigated hay, the balance being in non-irrigated pasture. Five horses are keptyear round on the private ground andthere is enough hay left over to keep 40mature cows for 30 days at headquar-ters. Weaned replacement heifers arekept at headquarters and fed hay for 1week and then graze hay stubble for 1week. Following this, they are put outon a pasture near headquarters untilthe first of January. For January andFebruary, replacement heifers arebrought back to headquarters and fedhay. After this time, they are put outwith the cow herd.

Let's look at the constraints that Johnhas with his operation. First, he islimited to two breeding pastures duringthe summer. Secondly, he mustmaintain or increase fleshing ability ofthe cowherd (no more than two Xs fromlean to fat ratio for biological typeslisted in Table 1). The second con-straint would imply that John notincrease milk production to any extentand that he maintain cow size ordecrease it slightly (no more than threeXs for mature size and no more thantwo Xs for milk production).

When the family reviewed their options,they decided they would like to keepthe disposition and “rustling ability” ofthe Hereford cows. With the two


pasture limitation, they decided toimplement a two stage crossbreedingprogram by first developing a herd ofF1 females and then crossing the 4-year-old and older crossbred cows to asmaller framed terminal sire (no calvingassistance rendered). The sire breedswhich fitted the family’s criteria wereAngus for the initial sires to produce F1females and Limousin for the terminalsire. Red Poll was considered briefly forthe initial sire breed due to the smallersize and younger age at puberty andthen eliminated due to the difficulty inobtaining bulls and the possibility ofincreased milk production. It was feltthat the Angus sires would reduce ageat puberty slightly (Clay Center hasadjusted age at puberty at 359 days forRed Poll, 393 days for Angus, and 411days for Hereford) and sires with lowbirth weight EPDs are readily available.The stages in implementing the cross-breeding program are as follows:

Stage 1: Replace all Hereford bulls withAngus with low EPDs for birth weight,yearling weight, and maternal milk.Keep as many of the replacements aspossible, allowing for a more rapidturnover to F1 cows. For two years,breed all cows to Angus bulls. From thefirst calf crop on, start selecting cross-bred bulls prospects from the herd atweaning. From weaning until the springof their yearling year, test bulls in homefeedlot and pasture for performance ona roughage based diet. Cull bullsaccording to performance and breedingsoundness examinations. Bull to cowratio for F1 bulls is 1:15 or 1:20 asyearlings and 1:33 as 2-year-olds.

Stage 2: At the beginning of the thirdbreeding season, a proportion of thebull battery is replaced with F1 bulls. AllF1 females over 4 years old will bebred to the terminal sires. When the

herd stabilizes at 100% F1 females,45% of the herd (younger cows) will bebred to F1 bulls for replacements and55% (older cows) will be bred to theterminal sires in a different pasture withall these calves being sold.

The possibility of inbreeding fromretained crossbreed bulls after theirthird and final breeding season is (onthe high side) about 6.5% if the herdstayed in a simple F1 breeding systemand about 3% for the combination F1/terminal sire crossbreeding program. Inthe future, some of this can be alleviatedby (a) buying crossbred bulls as theybecome more popular or (b) by estrussynchronizing the cow herd for 1 heatcycle and using mass AI with F1 AI siresas they become more available.

OTHER INFORMATION

Other information on crossbreedingsystems is available from the followingpublications:

Crossbreeding Beef Cattle for WesternRange Environments TB-88-1. 1988.D.D. Kress and T.C. Nelson. NevadaAgricultural Experiment Station, Col-lege of Agriculture, University ofNevada-Reno.

Crossbreeding Beef Cattle C-714.1990. D.D. Simms, K.O. Zoellner, R.R.Schalles. Kansas State University,Cooperative Extension Service, Man-hattan, KS.

Detailed information on breed groupaverages for different traits at ClayCenter, NB can be found on theInternet at

http://www.ansi.okstate.edu/breeds/research/marccomp.htm

1Area Extension Agent, Animal ScienceUniversity of Arizona


FROM:

Arizona Ranchers’ Management GuideRussell Tronstad, George Ruyle, and Jim Sprinkle, Editors.Arizona Cooperative Extension

DisclaimerDisclaimerDisclaimerDisclaimerDisclaimer

Neither the issuing individual, originating unit, Arizona Cooperative Extension, nor the ArizonaBoard of Regents warrant or guarantee the use or results of this publication issued by ArizonaCooperative Extension and its cooperating Departments and Offices.


Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, incooperation with the U.S. Department of Agriculture, James Christenson, Director, CooperativeExtension, College of Agriculture and Life Sciences, The University of Arizona.

The University of Arizona College of Agriculture and Life Sciences is an Equal Opportunityemployer authorized to provide research, educational information, and other services only toindividuals and institutions that function without regard to sex, race, religion, color, national origin,age, Vietnam Era Veteran’s status, or handicapping conditions.


Currently, most registered bulls haveinformation available from their ownperformance records, progeny, orrelatives which enables us to predictthe performance of future offspring forvarious traits. An expected progenydifference or EPD is the difference insome trait (usually expressed aspounds, but sometimes as inches forcarcass type traits) which one canexpect when compared to other ani-mals of the same breed. For example, ifa bull’s birth weight EPD is +5.0, thenon an average his offspring shouldweigh 5 lbs. more at birth than does abull with a birth weight EPD of 0. Theactual difference you will realize withinyour herd for a particular trait willdepend upon how your herd comparesto the breed as a whole. For example, ifweaning weights on a particular ranchare greater than the observed breedaverage, then it is conceivable that abull’s weaning weight EPD in this herdmay be less than that listed for thebreed.

The traits which are commonly avail-able for sires include birth weight,weaning weight, yearling weight, milk ormaternal milk, and total maternal. Forall of these traits, an EPD is expressedin pounds deviation + or - from thebreed base average of 0. (Note: Thebreed base average is often outdatedby several years, so actual baseaverages for a given year often exceed0.) It must be pointed out that milk EPDvalues are not pounds of milk, but thepounds of weaning weight in theoffspring of daughters of a bull whichcan be expected due to milk productionalone. In explanation, an EPD value of+12 for milk means that on average youcan expect grandsons and grand-daughters of calves from a bull’sdaughters to weigh 12 lbs. more at

weaning due to the influence of milkproduction in the daughters. Totalmaternal EPD values in grandsons andgranddaughters are total pounds ofweaning weight expected due to thecombined influence of milk productionand growth genetics from dams.

Accuracy (often shown as ACC) is theamount of confidence one can place inthe estimated EPD. This accuracyfigure is related to the number ofprogeny of a particular bull for whichrecords exist. An accuracy of .93basically means you are 93% confidentthat the bull’s EPD will be what therecord says it is. An accuracy of .40would be more unreliable. Young,unproven bulls have low accuracyfigures.

The EPD values for a bull must becompared within a breed. A birth weightEPD of +5 for a Charolais bull wouldnot have the same effect upon calvingdifficulty as a +5 for an Angus bull in acommercial crossbred herd becausebreed averages are different. Therespective breed averages for aparticular year can usually be obtainedby contacting breed associations orreviewing breed sire summaries. Table 1contains information from more than4,000 offspring (from Angus x Hereforddams) along with 30 sires per breed.This data was collected in one environ-ment only (Clay Center, Nebraska) andsires were adjusted for 1991 EPDbreed averages. Some of the respectiverankings may change as cattle movefrom one environment to another.

In order to utilize heterosis and com-bine complementary breeds in cowherds, crossbreeding is practiced. Onemay be concerned about matchingcattle to the environment or in meetinga particular marketing niche. To aid inthese decisions, EPDs across breedscan be estimated using Table 1 and theindividual bull EPDs. The actualdifference between bulls of differentbreeds can be estimated by adding theEPDs to the respective breed averages

UNDERSTANDING EPDS

Jim Sprinkle1


Table 2. Across Breed EPDs for Some Traitsa

a EPDs adjusted to a 1992 base with Angus EPDs set to zero in MARC’s GPEproject. From Barkhouse et. al., 1994. Proc. Beef Improvement Federation 26thResearch Symposium and Annual Meeting, West Des Moines, Iowa. June 1-4,1994.

and then comparing the resulting sums.For example, assume we wish tocompare a Charolais bull with a birthweight EPD of +4 and an Angus bullwith an EPD of +6. Using the breedaverages from Table 1, progeny of theCharolais bull should be 6.4 lbs.heavier at birth than Angus progeny atClay Center, Nebraska.

[(86 + 4) – (77.6 + 6)]Charolais Angus

In this example, the Charolais bull isexpected to sire calves with heavierbirth weights than the Angus bull eventhough the birth weight EPD wasgreater for the Angus bull. While thismethod does not fully account for theeffects of heterosis when combiningmales and females of two unlikebreeds, it is a good starting point forplanning breeding programs.

If you have an idea of what your herdaverages are for various traits, Table 2may be more useful to you. Table 2allows comparison of EPDs acrossbreeds with Angus EPD values beingspecified as 0 for all traits. For example,an Angus bull with a birth weight EPDof +5 should sire calves with birthweights 5 lbs. heavier than the averageAngus bull. If you used a Limousin bullin your commercial herd with a birthweight EPD of +2, then you couldexpect him to sire calves weighing 8.6lbs. (2 + 6.6) heavier than an averageAngus bull. Table 2 information is alsofrom Clay Center, Nebraska and will notcompletely account for changes in breedrankings with different environments.

Expected progeny differences can beused as a tool to predict future perfor-mance and to plan goals for geneticimprovement in your cow herd. Avail-able resources should be evaluatedand genetic change should be plannedto match these resources. In planninggenetic trends in your herd, it should beremembered that one genetic trait isoften correlated with another. Forexample, as yearling weight increases,

deerBhtriB

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gnilraeYthgieW thgieW thgieW thgieW thgieW

sugnA 8.77 144 018

drofereHdelloP 3.08 054 608

drofereH 4.18 244 008

nrohtrohS 5.38 164 238

namharB 8.78 744 447

latnemmiS 0.68 174 068

nisuomiL 1.38 054 897

sialorahC 0.68 854 918

uojnA-eniaM 8.78 854 628

heivbleG 3.78 564 228

reuagzniP 4.28 044 387

srelaS 9.08 464 038

Table 1. Breed Averages for Some Traitsa

a Averages of offspring sired by bulls with EPDs in MARC's GPEproject. Adjusted for 1991 EPD breed averages. From Beef,September 1993.

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drofereHdelloP 9.5 3.11 4.72- 8.8

drofereH 1.6 4.6 7.3- 3.7

nrohtrohS 7.8 2.52 9.11 9.13

namharB 8.31 8.82 4.43 1.12-

latnemmiS 5.01 8.94 4.52 2.97

nisuomiL 6.6 8.82 5.8- 0.02

sialorahC 7.9 2.73 7.3 4.25

uojnA-eniaM 9.11 5.13 1.32 7.93

heivbleG 6.9 6.83 1.72 8.14

reuagzniP 7.8 6.12 1.7 4.61

esiatneraT 4.4 3.22 1.02 5.01

srelaS 8.6 8.03 9.11 7.13


so does birth weight and matureweight. An environment with 10 inchesof rainfall may not be the place to use asire with a yearling weight EPD of +70unless all replacement heifers werepurchased elsewhere. Otherwise,mature weight of the cows will increase.In arid western climates with limitedforage availability, oftentimes the use ofsmaller cows is required to obtainacceptable conception rates. Bulls withlow or negative birth weight EPDsshould be used on first calf heifers.High milk production may be a liabilityin arid environments, so milk EPDvalues should be moderate. TheAmerican Angus Association reportedthe observations of a breeder who hadevaluated EPDs in a range operation.He suggested that for Angus cattleunder range conditions, an EPD formilk from -5 to +9 was adequate for calfgrowth and still allowed for rebreedingsuccess.

In addition to using EPDs in chartinggenetic change, ranchers with commercialherds can predict genetic change intheir herds with the formula below.When this value is divided by 2(parents only contribute 1/2 of theirgenes to offspring), it approximates anEPD value on a herd-wide basis.

Genetic change/generation =h2 • selection differential

The heritability (h2) of birth weight isaround .35 to .50, for weaning weight itis around .25 to .30, and for yearlingweight around .40

The selection differential is the differ-ence between selected individuals for a

specific trait (e.g. weaning weight) andthe average for all animals by sex in theherd. For example, the selectiondifferential would be 60 lbs. if heifersat weaning averaged 400 lbs. andselected heifers weighed 460 lbs.When calculating selection differentials,it is important for the animals beingcompared to have been treated simi-larly. In other words, if one group ofselected heifers were grazed onirrigated pasture and another groupwas grazed on rangeland, it would notbe appropriate to compare thesegroups without applying a weaningweight discount to the irrigated pasturegroup.

An example in calculating geneticchange is shown below. Selectedheifers weigh 60 lbs. more at weaningthan the average of all heifers in theherd. The heritability of .25 is multi-plied by .60 to give 15 lbs. geneticsuperiority.

60 lbs. • .25 = 15 lbs.

This must be divided by 2, since theheifers will only contribute 1/2 of thegenes to offspring. Therefore, 7.5 lbs.will be added from the female side. Aselected bull has a weaning weightEPD of +25 lbs. when used in yourherd. Therefore, the predicted increasein weaning weight for the selectedheifers and this bull would be 32.5 lbs.

The above example shows theresponse per year which can beexpected for single trait selection.Selecting for more than one trait at atime usually reduces the genetic changeexpected in single trait selection.

1Area Extension Agent, Animal ScienceUniversity of Arizona


FROM:

Arizona Ranchers’ Management GuideRussell Tronstad, George Ruyle, and Jim Sprinkle, Editors.Arizona Cooperative Extension

DisclaimerDisclaimerDisclaimerDisclaimerDisclaimer

Neither the issuing individual, originating unit, Arizona Cooperative Extension, nor the ArizonaBoard of Regents warrant or guarantee the use or results of this publication issued by ArizonaCooperative Extension and its cooperating Departments and Offices.


Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, incooperation with the U.S. Department of Agriculture, James Christenson, Director, CooperativeExtension, College of Agriculture and Life Sciences, The University of Arizona.

The University of Arizona College of Agriculture and Life Sciences is an Equal Opportunityemployer authorized to provide research, educational information, and other services only toindividuals and institutions that function without regard to sex, race, religion, color, national origin,age, Vietnam Era Veteran’s status, or handicapping conditions.

13 spec lines for beef breeding - university of arizona · breeder. the first calves were dropped...

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