192003 Armidale Feeder Steer School

Growth, maturity and carcase specificationsNSW AgricultureBeef Industry Centre, UNEArmidale NSW 2351Ph: 02 6770 1812Fax: 02 6770 1830Email: bob.gaden@agric.nsw.gov.au

Bob Gaden

Session 2a

IntroductionThe aim of this session is to set a simple foundation for understanding the main principles ofgrowthandmaturity.Thisisthebasisfordecidinghowtofindthebestcombinationofframesize,muscling,breedtypeandnutritiontomeetmarketspecificationsforweightandfatdepth.

A general growth curveLet’simagineFigure2a-1isthegrowthcurveforatypicalsteerfrombirthtomaturity,withadequatenutritiontomeethisbasicneeds:

Astheanimalgrowsfrombirthtomaturity,therearechangesintheproportionoffat,muscleandbone(Figure2a-2).

Stage 1Stage 1

CalfCalf

GrowoutGrowout

FinishFinish

AgeAge

WeightWeight

Three phases of growth

Stage 2Stage 2 Stage 3Stage 3

BoneBone

MuscleMuscle

FatFat

Figure 2a-1. General growth curveAgeAge

WeightWeight

Composition of growth

bonebone

musclemuscle

fatfat

Figure 2a-2. Composition of growth

Stage 1 - Birth to weaning (say 6-7 months)After birth, bone growth is first priority, toestablish frame for future body growth. Newmuscle cells are being formed and muscleweight increases rapidly.Fat is onlydepositedinsmallquantities.

A calf requires nutrition of very high qualityto develop bone and muscle, and this ismainly ensured by milk from its mother.Inadequatenutritionatthisstageaffectsfuturedevelopment.

The carcase at this stage has a high bonecontent, high muscle, low fat, with low gutweight.

Themeatfromcalves istender,has littlehardconnectivetissue,andnotmuchflavour.

Stage 2 - Growing outInmidgrowth(sayafterweaningat6-9months)bone growth continues but the animal’s mainpriority becomes muscle growth. Normally, fatisonlydepositedinsmallquantities.Thisisthe“backgrounding”or“growingout”phase.

The growing animal requires high qualityprotein-rich diet, and the rate of developmentduring this phase is very sensitive to feedquality.

After weaning, gut weight increases markedlyto cope with digesting roughage diets – thiskeeps dressing percentage down. The carcaseitselfhasanincreasingratioofmuscletobone,andverylittlefat,sogenerallyhasahighyield(percentageofsaleablemeat).

Meat is tender at this vealer/yearling stage,

20 2003 Armidale Feeder Steer School

andhasmoreflavour.Fatteranimalsgenerallyhavebettereatingquality,withlessriskofcoldshorteningandenhanced juiciness fromsmallamountsofmarbling.

Stage 3 - Finishing/maturingWhengrowthofbone is largelycompletedandallmusclecellshavebeenestablished,allthatisleftisformusclecellstofillout,andafterthat,surplusenergyisstoredasbodyfat.

Asanimalsmature,theycanexistonquitepoorqualityfeed,butiffeedqualityisgood,theycanexpresstheirmusclepotentialandaccumulatefatveryquickly.

As fattening takes place, fat is deposited inthe gut and carcase depots (subcutaneous orselvedge fat, intermuscular or seam fat, andintramuscular or marbling fat). The carcasebecomes an increasing proportion of the totalbody,sodressingpercentagerises.Theyieldofsaleablemeatinthecarcasefallsastheneedforfattrimmingrises.

Meat flavour reaches its maximum in theprime cuts of amature, finished steer, but asconnective tissue increases with age, thereis a decline in tenderness, especially in thesecondarycuts.

Cattle with different growth curvesSex

Heifers–giventhesameaccesstonutritionassteers,heifersgrowalittlelessbone,considerablylessmuscle,andputonconsiderablymorefat.They follow a “flatter” growth curve with anearlierendpointi.e.areearlier maturing.

Bulls – they grow moremuscle and bone, andare less inclined to putonfat.Theyhavealongerperiod in Stage 2 andgreateramountofmuscleinStage3–theyarelater maturing.

Frame size

Large framed cattle growtoahighermatureweightandtakealittlelongertoreachmatureweight(latermaturing).

Small framed cattle growtoalightermatureweightand get there earlier(earliermaturing).

Muscling

Heavilymuscled cattle at the same frame sizetake a little longer in Stage 2 to fill out theirmuscling, and carrymoremuscle and less fatlater in life. They are heavier, and effectivelylater maturing than average-muscled cattle ofthesameframesize.

Lightlymuscledcattlearelikeheifers,andfinishtheir muscle growth earlier and at a lighterweight,puttingthesurplusintoextrafat.

CattlethatareBOTHlargeframedANDheavilymuscled,suchasmostEuropeanbreed types,canbeverylatematuring.Thismeanstheyarevery difficult to fatten at lighter weights, andneedtobecarriedtoveryheavyweightstofinishadequately.

Maturity and market specificationsMarket specifications are mainly described intermsofage,sex,weightandfatdepth.Asmostof our target markets focus on young growingsteers,weight and fat depth are the twomainfactorstothinkabout.

It is therefore important to know what makescattleputonfatfasterorslowerastheygrow.Thiswilldeterminewhethertheyare“finished”and meet the target specifications for anyparticularmarket.

Changing the growth curve for a particular animalThere aremany factorswhich can change theactual growth path of a particular animal,and therefore arrive at different combinationsof weight and fat depth, to determine market

suitability. The mainfactorsarenutritionandgenetics.

Nutrition

Nutrition in Stage 1

Ifnutritionisbetterthanadequate, it allows fulldevelopment of potentialbone and muscle, andmay even allow somesurplus to be depositedas fat. Such calves arehighly sought after forslaughter as vealers at7-10months.Iftheyhaveadequate frame size andmuscling, they still havethe potential to grow onand mature at heavyweights.

212003 Armidale Feeder Steer School

On the other hand, severe restriction inStage 1 results in impaired bone and muscledevelopment–thesecalvesdon’tcatchupwhentheyareputongoodfeedlater,andwillproducecarcases with lighter weight, less muscle andmorefat.Bewaryofbuyinglightweightweaners(sayunder180kg)tofinish,andbeawarethatearly weaned calves requires special attentionto their nutrition, to ensure they retain theirpotential.

Nutrition in Stage 2

Cattle receiving better than their basicrequirementsforgrowthinStage2canproduceplentyofmuscleanddepositsomefat.Mostofourtablebeefqualitydomesticandexportcattleareslaughteredinthisstageoflife,around50-70% of mature weight. High quality pasture,forage crops or feedlots will provide the goodnutritionrequiredtofinishcattlewhiletheyarestillactivelygrowing.

Restriction of nutrition in Stage 2 affects thesizeofmusclefibres,butiftheyhavehadagoodstartinlifethiswillbetemporaryandreversible.On returning to good feed they will recover,expressing compensatory gain. Fat depositionwillbedelayedalittle,resultinginleaner,higheryielding carcases. These benefits are used bycattlefinisherstoenhancetheirprofit.

Nutrition in Stage 3

InStage3,cattlefinishthedevelopmentoftheirbone and muscle structure. They can gain orlose weight according to available nutrition,withthemaineffectbeingontheproportionofbodyfat.

Recovering from poor condition, they fill outtheirmusclesfirst–thishappensquicklywhentheyhavefinishedgrowing-and thenput thesurplusbackonasfat.

Maturecattleareveryeasyandquicktofinish,once relievedof theirbreeding responsibilities,provided of course that they are sound(especiallyteeth)andhealthy.

VirtuallyallsteersareslaughteredbeforeStage3, so the main cattle in this group are cullfemalesandbulls.

Genetics

Breed effects

The main breed effects on maturity andcarcasecompositioncanbeexplainedintermsof muscling and frame size. Be aware thatgeneralisingisdangerous-thereisawide(andgrowing)variationbetweenanimalswithineachbreedinframesizeandmuscling.

Somebreedsgenerallyhavelargerframesizee.g.

Charolais,Simmental.Thesearelatermaturingandfinishatheavierweights

TheBritishbreedstendtohaveamoremoderateframe size, and finish at moderate weights.SomeBritishbreedshaveincreasedtheirframesize andmature weight significantly in recentyears.

Breeds which are strong in muscling (highmuscle to bone ratio) produce higher yieldingcarcases and are often prominent in carcasecompetitions.TheLimousinisaheavilymuscledbreedwithamoderateframe-itproduceshighyielding carcases at heavy weights, while theMurrayGreyhasasmallerframe,andproduceshigh yielding carcases at more moderateweights.

Breeds which are BOTH large framed ANDheavilymuscledwillbeverylatematuring.

Selection within breeds

It is very difficult to breed to amaturity typeif you select your bulls by eye, because whatyousee-theirframe,muscleandfatness-arestrongly influenced by non-genetic aspects oftheirupbringing.

In most breeds, BREEDPLAN produces EBVswhichproducerscanuse toselectsireswhichwill fine-tune carcase yield, fatness andmusclingandmaturesize.

Final commentsMatching genetics, nutrition and marketsuitability is a three-dimensional challenge,especially as all of them are dynamic. Cattlewithmoderateframesizeandmediumtoheavymuscling are most versatile, because withreasonable nutrition they can produce high-yielding,moderncarcases,whichfitnearlyallofourmainstreammarkets.