ANSC 1000 Exam 2 Lecture 8-10
ANSC 1000 Exam 2 Lecture 8-10 ANSC 1000
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This 17 page Class Notes was uploaded by Brianna Notetaker on Saturday October 8, 2016. The Class Notes belongs to ANSC 1000 at Auburn University taught by Dr. Carolyn Huntington in Spring 2016. Since its upload, it has received 5 views. For similar materials see Introduction to Animal Sciences in Animal Science at Auburn University.
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Date Created: 10/08/16
ANSC 1000Exam 2 Lecture 8 Breeding 2 FundamentalQuestions 1.)Whatis the “best”animal? o Labradorwithshow-winningconformation? o Or onewith exceptionalretrievinginstinct? o Is the best dairycow theone thatgives the most milk? o Or onewith bestlegs, feet,uddersupport? Answers determinedirectionofgeneticchange for breeding operations 2.)How doyou breed animalssotheirdescendantswillbe,if not“best”, at leastbetterthantoday’sanimals? o How are animalpopulationsimprovedgenetically? Involvesgeneticprinciplesandanimalbreedingtechnology 1.)Whatis the “best”animal? “Best” is a relativeterm o Animalthatworks bestfor one environmentvs.anothermaybe quitedifferent Methodknownas “systems approach” o Requiresdetailedknowledgeoftraitsofimportance o Interactionwithenvironment,managementprocedures,costs, andprices TraitsshowContinuousVariation Most economicallyimportanttraits(milkproduction,egg production,growthrate,etc.) are controlledbyhundredsofpairs ofgenes Livestockhave100,000+ genes o Thinkbeyondoneor two pairsofgenes Likelyto havesomeheterozygousandsome homozygousgene pairs As genes expressthemselves,andthe environmentinfluences thesetraits,producersobserve & measuredifferences 2 StatisticalMeasurements Quantitativevs.QualitativeTraits Multipletraitscanbe measuredor described Quantitative=objectivelymeasured o Observationsexistalongacontinuum o Ex:growth traits,skeletalsize, speed Qualitative=descriptive,subjective o Ex:hair color,hornedvs.polled 3 Qualitative(SimpleInheritance) 1 – 4 pairsofgenes controlone trait Environmentplayslittle,ifany,role Examples o Coatcolor (normally1 – 4 pairs) o Dwarfism in cattle(normally1pair -recessive) o Polledor horned(1pair) Quantitative(ManyPairsofGenes AffectingOne Trait) Usuallytheones thatare ofeconomicimportance These traitsinclude: o average dailygain o feed efficiency o weaningweight or litter weight o yearlingweight (cattle) o loineyearea (alsocalledrib eyearea) o backfat thickness o muscling o frame size (cattle) o reproduction(littersize,calfcrop,twinning) Affected bymanypairsofgenes Possibly100 or more pairsinvolved o If ananimalis horned,itis pp;ifit is polled,itcan be eitherPP or Pp o However, ifI tellyou ananimalgains3.2 lb/dayandaskyou what thegenotype is,you wouldn'tbe ableto tellme Nobodyknowsthe answer o It has beenestimatedthatrateofgain has over14million possiblegenotypes Some genes may havean effect onmore thanone trait(called pleiotropy) Thismaybe good for your selectionprogram,or it couldwork againstyou Examples: 4 o Rate ofgainand feed efficiency – Some ofthe genes thataffect rate ofgain alsoaffect feed efficiency. Animalsthateatmore alsogain more, andare more efficient. o ADG andbackfat (BF)thicknessin hogs – Some ofthe genes that affect rate ofgain in hogsalso affect the amountoffat deposited.Fastergaininghogstend tobe fatter.Thiscreates a problembecausehogproducerswantfast-gaining,leanhogs. ChangingAnimalPopulationsGenetically As breeders,we want toknowthe most desirablephenotypesand genotypes P=G+E o P=phenotype o G=genotype o E=environment G is the portionthatisselectable o Controlledbygenes:i.e.,there are selectabledifferences Beyondvisualappraisal… P = G + E One approachisto make E (environment)thesame(common)for allanimalswithinacomparison(contemporary)group o P = G + Ecommon o Begins withdefinitionofcontemporarygroup 5 ContemporaryGroup A contemporarygroupis a groupof animalswiththesame: o Herd o Sex o Breed or breedtype o Birthseason o Weigh dates o Management Ratio Comparecalves for a traitwithina contemporarygroup. Average ratioofa group is 100 WhatMakes AnimalsDifferent Some differences are dueto somethingotherthangenes (undefinedvariability) Environmentaldifferencesinclude: o Nutrition o Health o Weather o Injury o Management o Fertilityofthe sire anddam o Time ofmatingduringthe heatperiod o Seasonofthe year Environmentaleffectscan be knownor unknown 6 Known -havean average effect onindividuals o Ex:Age, age ofdam, gender Unknown- randominnatureandmore difficulttocontrol Breeders useadjustedrecords AdjustedData Adjustments o Age of Dam o Age of calf Records o Adjustedbirthweight o Adjusted205-dayweight o Adjusted365-dayweight o Adjusted365-dayhipheight o Adjusted365-daypelvicarea o Adjusted365-dayscrotalcircumference Breed specific adjustment for age AdjustmentGuidelines Adjustmentequationscanbe foundatthe Beef Improvement Federationwebsite: (www.beefimprovement.org) Clickon theGuidelinessection WeaningWeightAdjustment 7 8 P = G + E 9 ANSC 1000Exam 2 Lecture 9 ExpectedProgenyDifferences (EPDs) Whatis an EPD? A predictionoffutureprogenyperformancerelativeto some standard EPDs are designedtocompare animals,nothingmore! How are EPDs calculated? EPDs are calculatedusingstatisticalproceduresthattakeinto accountlarge amountsofinformation o Individual’sownrecord o Ancestorandprogenyrecords o Heritabilityofthe trait o Geneticcorrelationoftrait withothertraits CanEPDs be comparedacross breeds? No.Different breedshavedifferentbases(standards) Breed associationsareagreeingto finda common baseyear (e.g., average geneticvalueof allcalves bornin 1975) Heritability(h ) The portionofthe phenotypic(observed)variationinatraitwhich can be attributedtotransmissiblegeneticeffects (i.e,additive geneticeffects) Heritabilities 10 2 Higher h resultsina greater responsetoselection. CorrelatedResponses Geneticchange seen in traitsnotdirectlyselected for Canbe a positiveor negativeresponse GeneticCorrelationGeneralities Higher weaningand yearlingweights aregenerally associatedwith higherbirthweights Higher growth rates are generally associatedwithlarger scrotal circumferences andribeyeareas Higher growth EPDs are generally associatedwithlower maternal milkEPDs Higher maternalmilkEPDs are generally associatedwithhigher marblinginprogeny EPDs Do not predictperformance,butdo predict differences in performance Are onlyas good as thedatagoingintothe system Best predictorofgeneticworth Do not change Do account for preferentialmatings Types ofEPDs Direct andMaternalEPDs Weaningweight o Calf’sown genes – inherentabilitytogrow-EPD weaningweight o Genesof thecalf’s dam – nutritionalenvironment,i.e.,milk - EPD milk EPD WWT reflects theexpected weaningweight performanceof a bull’scalves 11 EPD reflects thatportionofexpectedweaningweight MILK performanceof a bull’sdaughters’calvesinfluencedbyher milking ability ProductionEPDs – Direct Birthweight Calvingease Weaningweight Yearlingweight Yearlingheight Scrotal circumference ProductionEPDs – Maternal Milk(WW) Scrotal circumference Calvingease Heifer pregnancyrate Stayability CarcassEPDs Carcassweight Marbling Ribeyearea Backfat % RetailProduct UltrasoundEPDs % Intramuscularfat Ribeyearea Fat 12 How doI use anEPD? ComparingEPD BWTfor Sires A andB of theSame Breed The DIFFERENCE is what’simportant! ComparingEPD BWTfor Sires A andC ofthe Same Breed The DIFFERENCE is what’simportant! 13 The problemisthatwe stilldon’tknowwhatto expect in terms of calfbirthweights ifwe use BullA. Shouldwe use BullA on heifers? We need to lookat thebreed average for EPD Birth weight ComparingEPD BWTfor Sire A to the BreedAverage Calfbirthweights for Sire A willbe 1.1 lbs.lighterthanthe“average sire”in the breed(withinthe siresummary). Are EPDs thatare equalinvalueequallyreliable? No.Theyare not. ReliabilityofanEPD is expressedinterms of ACCURACY. Accuracy valuesrange from 0.00 to 1.00 As Accuracy approaches1.00,theEPD is more reliable PossibleChangeofEPD WWT at VaryingAccuracies 14 ComparativeReliabilityofEPD WWT Factors AffectingAccuracy Amountofperformanceinformationavailableforanindividual,its relatives,andcontemporaries–More is Better Numberof progenyhas thegreatest potentialforimprovingaccuracy Heritabilitiesandgeneticcorrelationsamongtraits How doI interpretaccuracy? 15 SortingThrougha “Sea” of Data Determinewhich traitsare importanttoyourproduction/marketing goals Use informationinbreedsiresummaries o Currentbreedaverages for EPDs o EPD percentage breakdown BreedingAverage EPDs WhatMakes AnimalsDifferent? Cannotselectfor environmentaldifferencesandcarryit intothe next generation Examples: o Litter size inhogs – Mostdifferences are environmental;will make most improvementthroughbettermanagement(Avg. littersize inU.S. increasedonly~1/2 pigoverlast15-20 years, from 7.1 to 7.7 pigs marketed.) o Frame size in cattle– Mostdifferences are genetic. Cattlehave gottenmuch tallerin the U.S.since 1970. Producers haveput emphasisonframe size intheir selectionprograms 16 How are AnimalPopulationsImproved? Purposeofbreedingis to geneticallyimprovepopulations,notjust individuals Two basictools: o Selection which are to be parents;howlongtheyremainin breedingpopulation o Mating whichmale bred towhich female Bothtoolsinvolvedecisionmaking! 17