Predicting Breeding Value

Breeding Value (BV)

• Genetic merit of an animal for a given trait.

• Often expressed as a deviation from herd or group average.

Breeding Value (BV)

• In real life we observe the phenotype but want to estimate the breeding value (or its genetic additive effect)

Breeding Value (BV)

• We observed that the phenotype of a given animal is 630 lbs at Weaning

• But what is its breeding value (i.e. values of its genes to its offspring)?

Some DefinitionsPredicting Genetic Gain

• Breeding Value (BV): The value of an animal as a (genetic) parent.

• Breeding Value: The part of an individual genotypic value that is due to additive effect and therefore transmittable. (Breed true)

• Independent Gene Effect: The effect of an allele is independent of the effect of the other allele at the same locus (dominance) and the effects of alleles at other loci (epistasis). ADDITIVE EFFECT.

• Estimated Breeding Value (EBV): An estimation of a breeding Value.

Some DefinitionsPredicting Genetic Gain

• Independent Gene Effect: The effect of an allele is independent of the effect of the other allele at the same locus (dominance) and the effects of alleles at other loci (epistasis). ADDITIVE EFFECT.

• Estimated Breeding Value (EBV): An estimation of a breeding Value.

• Additive Genetic Value = Breeding Value.

• “Breed True" (i.e., average offspring performance closely approximates average parent performance assuming constant environment)

Genotypic Value is not the same as

Breeding Value

• Genotypic Value of an animal is the value of its genes on itself and includes Additive, Dominant and Epistatic Effects.

• Breeding Value is the value of its genes on the progeny and is related to the Additive Effects (Breed True and narrow sense heritability)

Progeny Differences

• Progeny Difference (PD) or Transmitting Ability (TA): Half of an individual’s breeding value. The expected difference of the individual’s progeny and the mean performance of all progenies.

• Expected Progeny Difference (EPD) or Predicted Transmitting Ability (PTA): A prediction of a progeny difference.

Expected Progeny Difference (EPD) or Predicted Transmitting Ability (PTA):

The expected difference of the individual’s progeny and the mean

performance of all progenies.

• Its called prediction because its an estimation of the future performance of the animal’s offspring in relation to all progenies

Breeding Value (BV)

• The contribution of each effect is proportional to the variance explained

by effect

PV

VA

P

A

Additive Effect Dominance Environment

or Breeding Value

PV

VE

P

EPV

VD

P

d

• Concepts discussed on Phenotypic Selection still valid!!

Estimated Breeding Value (EBV)

• Notice that the Breeding Value of an animal is the sum of its genes Additive Effects

PV

VA

P

Aˆ

Additive Effect Breeding Value Genetic Gain

When estimated from Phenotypes Phenot. Selection

Phenotype expressed as

a deviation from the mean

PV

VBV

P

A ShG 2

• Concepts discussed on Phenotypic Selection still valid!!

EPD or PTA: Half of an individual’s breeding value (BV).

• A parent passes 1/2 of its BV to an offspring.

• The other half comes from the other parent

• On phenotypic selection the gain is determined by selection differential averaged for males and females

Estimated Breeding Value (EBV)

• Actual BV is unknown for most traits.

• We can estimate BV of an animal based on performance of the animal itself and its relatives.

• Similar to EPD, PTA, etc.

• Animal of Interest

– Animal whose BV is being estimated.

• Animal(s) of Record

– Animal(s) being evaluated or measured. Can be the animal of interest and(or) relatives.

Predicting Breeding Value

• Phenotypic deviation from a contemporary mean!!

• Population mean• Herd or flock mean• Mean of animal born in same management

group

• It’s a way to correct for non- genetic effects

Predicting Breeding Value

Population

FarmsContemporary

Groups

Predicting Breeding Value

PopulationFarms

Contemporary Groups

Animals Compared within Contemporary Group.It’s a way to correct for non- genetic effects.

Reference Sires = Animal used in different contemporary groups or different farms.

Mean production of Half Sibs from Reference Sires allows the estimation of the effect of the contemporay group.

Once the contemporary group effect is calculated is possible to compare animals born in different farms.

Within Contemporary GroupAnimals have performance adjustedfor non-genetics effects such as age of the Dam

General Formulas for BV and ACC

• P = trait mean of the animal(s) of record.

• trait mean of contemporary group.

• g = relationship weighting factor.

• b = regression factor.

)( PPbBV

P

PV

VBV

P

A

Accuracy (ACC) of EBV

• Mathematical expression of the degree of confidence that the EBV accurately predicts true BV.

• Ranges between 0 and 1.

General Formulas for EBV and ACC

• g = relationship weighting factor.

• b = regression factor.

gbACC

EBVEBVrACC

,

Correlation between real breeding value and estimated breeding value

i.e. the closest the estimation to real BV more accurate is the EBV

Mixed Models