Predicting Breeding Value

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Predicting Breeding Value
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Breeding Value (BV)

• Genetic merit of an animal for a given trait.
• Often expressed as a deviation from herd or group
  average.

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Breeding Value (BV)

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

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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)?

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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.

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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)

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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)

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Progeny Differences

• Progeny Difference (PD) or Transmitting Ability
  (TA) Half of an individuals breeding value. The
  expected difference of the individuals progeny
  and the mean performance of all progenies.
• Expected Progeny Difference (EPD) or Predicted
  Transmitting Ability (PTA) A prediction of a
  progeny difference.

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Expected Progeny Difference (EPD) or Predicted
Transmitting Ability (PTA) The expected
difference of the individuals progeny and the
mean performance of all progenies.

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

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Breeding Value (BV)

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

• Concepts discussed on Phenotypic Selection still
  valid!!

Additive Effect Dominance
Environment or Breeding Value
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Estimated Breeding Value (EBV)

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

• Concepts discussed on Phenotypic Selection still
  valid!!

Additive Effect Breeding Value
Genetic Gain When estimated from Phenotypes
Phenot. Selection Phenotype expressed as a
deviation from the mean
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EPD or PTA Half of an individuals 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

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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.

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• 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.

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Predicting Breeding Value

• Phenotypic deviation from a contemporary mean!!
• Population mean
• Herd or flock mean
• Mean of animal born in same management group
• Its a way to correct for non- genetic effects

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Predicting Breeding Value
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Predicting Breeding Value
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.
Animals Compared within Contemporary Group. Its
a way to correct for non- genetic effects.
Once the contemporary group effect is calculated
is possible to compare animals born in different
farms.
Within Contemporary Group Animals have
performance adjusted for non-genetics effects
such as age of the Dam
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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.

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Accuracy (ACC) of EBV

• Mathematical expression of the degree of
  confidence that the EBV accurately predicts true
  BV.
• Ranges between 0 and 1.

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General Formulas for EBV and ACC

• g relationship weighting factor.
• b regression factor.

Correlation between real breeding value and
estimated breeding value i.e. the closest the
estimation to real BV more accurate is the EBV
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Mixed Models