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P REDICTING BREEDING V ALUE

Management of candidates for selection Adjusting records of performancePredicting the values of individual animals

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M ANAGEMENT OF CANDIDATES FORSELECTION TO DISENTANGLE THE EFFECT

OF GENE AND ENVIRONMENTDifficult to identify with certainty the animals thathave been affected by subclinical diseaseDiscard the performance records from animals that

clearly have been affectedImportant to give animals equal opportunity (bornover a relatively short period of time, on the samefarm, and fed and managed similarly)to express theirgenetic meritThese animals called contemporaries and groups theybelong was called contemporary groupWill improve the accuracy of selection

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A DJUSTING RECORDS OF PERFORMANCE

Additive correction factors

Involve adding amount to (or subtracting amount from)the performance records of animals which belong toparticular classes such as singles or twins

On average the singles were 3 kg heavier than twins forlambs weight at weaning

Add 3 kg to the weaning weight of all twin lamb (orsubtract 3 kg the weight of all single lambs) to create aset of adjusted records.

Then all the lambs could be compared as a single groupand those with the heaviest adjusted weights selected

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A DVANTAGE OF A DDITIVE CORRECTIONFACTORS

Easy to useMake no assumption about the average geneticmerit of animals in different contemporary

groups

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D ISDVANTAGE OF A DDITIVE CORRECTIONFACTORS

Many record of performance are needed to estimatecorrection factors accuratelyHave to be estimated from data prior to the selectionof animals

May be fairly specific to a particular herd, flock ormanagement systemCan over-correct records of performance and removesome genetic differences. Eg. If CF were estimated fora flock in which two rams had been used and by

chance the genetically largest ram had more singleborn offspring. The effect of being born as a singlelamb could be over estimated due to part of theadvantage to singles was in fact due to having agenetically heavier ram.

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M ULTIPLICATIVE CORRECTION FACTORS

The records of performance are adjusted bymultiplying by the CFEg. Let say that triplet 4% lighter than twins,

and so multiply all weight from triplets by 1.04 tobring them to the level expected for twin.

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S TANDARDIZING TO ADJUST RECORD

A method of adjusting records involve assigning recordsborn in a specified time period to a contemporary group,based on the factors to be adjusted for.Within each of these groups each record is then expressedas a deviation from the mean of the group, in standarddeviation units.Eg. Records from lambs born over a period of a few weeks(a season) could be assigned to 4 groups: single reared from2 yr old dams: single reared from older dams: multiplereared from 2 yr old dams: single reared from older dams:

The mean and sd of the trait concerned are then calculatedseparately for each of 4 groups. Finally the performancerecord of each animal is expressed as a deviation from themean of its own group and then divided by the sd forthat group. This gives records expressed in sd units(typically ranging from about -3 to about +3.

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P REDICTING BREEDING VALUE

PBV or EBVThe clues we can use to predict BVs are recordsof performance from:

the animal itself the animals ancestorThe animals full or half sibsThe animals progeny

Any other relatives of the animalsCombination of the classes of relatives listed

above

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U SING THE ANIMAL S OWN PERFORMANCE

The simplest caseThe deviation in performance fromcontemporaries, multiplied by the heritability of

the trait concernedh 2 x (x i x p )

The animals rank in exactly the same orderwithin a herd as they rank on their performancerecord or on their deviation from the mean of contemporaries. However the PBV predicts howmuch of the superiority or inferiority in theanimals performance is due to its genes.

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F EATURES OF PBV

Can have +ve or ve value, or zeroThe sign indicates whether they are expected tobe genetically above or below mean of the group

They span a narrower range than the deviation sin performance - this regression or shrinkingreflects the fact the part of variation inperformance is environmental. For an animalwith a single record of performance theregression coefficient is simply the heritability of the trait concerned.

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U SING INFORMATION FROM RELATIVES

The simplest case is when records available fromthe parents.PBV offspring = PBV sire + PBV dam

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TERIMA KASIH