EPDs: Unraveling the Alphabet

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EPDs Unraveling the Alphabet

• J. Benton Glaze, Jr., Ph.D.
• Animal Veterinary Science Department
• University of Idaho

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Introduction

• The major objective (aim) of all beef producers
  should be to increase genetically the producing
  ability of cattle in their herds
• Genetic improvement is only possible if the
  breeding stock are, on the average, superior to
  the animals in the breeding herd the previous
  year of generation

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Introduction

• Selection of beef cattle is an attempt to
  identify and retain the best animals in the
  current generation to be parents in the next
  generation
• Improvement made through selection is dependent
  upon the genetic superiority of the selected
  animals

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The Genetic Model

• Phenotype (P) Genetics (G) Environment (E)
• Phenotypic value measure of performance for a
  trait in an individual animal
• Genotypic value effect of an individuals genes
  on its performance for a trait
• Environmental effect effect that external
  (non-genetic) factors have on animal performance

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Terms Used in Animal Breeding

• Heritability (h2) measure of the strength of
  the relationship between breeding values and
  phenotypic values (Values range from 0 to 1)
• Measures the amount of variation in a trait that
  is due to genetics
• Provides an indication of the amount of genetic
  change that can be made through selection

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Terms Used in Animal Breeding

• Genetic Correlation (rg) measure of the
  strength of the relationship between the breeding
  values of one trait and the breeding values of
  another trait (Values range 1 to 1)
• Describes the genetic relationship between two
  traits
• Indicates how one trait will respond to selection
  given that another trait is the one under
  selection

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Terms Used in Animal Breeding

• Contemporary Group group in which animals of a
  given sex and age, having similar treatment, are
  given equal opportunity to perform

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Expected Progeny Differences

• EPD a prediction, based on available data, of
  what the animal is expected to transmit to future
  offspring expressed as a difference in the trait
  unit (e.g. pounds, inches, centimeters)
• EPD an estimate of the expected performance of
  an animals offspring
• EPD a prediction of progeny difference

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Expected Progeny Differences

• EPDs do not predict performance
• EPDs predict differences in performance
• EPDs do change and are not static
• EPDs are as good as the data going into the
  system
• EPDs are currently the best predictor of genetic
  worth

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Calculation of EPDs

• EPDs are obtained from genetic evaluation systems
  based on BLUP which accounts for
• Environment and management differences among CG
• Genetic merit of mates
• Performance of individual, relatives, and progeny
• Genetic trend

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Types of Expected Progeny Differences (EPDs)

• Parent EPDs
• Non-Parent EPDs
• Pedigree EPDs
• ½ Sire EPD
• ½ Dam EPD
• Interim EPDs

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Expected Progeny Difference- Example -

• A producer is interested in improving YWT in his
  herd, and has the choice of purchasing Bull 1
  with a YWT EPD of 60 and Bull 2 with a YWT EPD
  of 50
• Difference between 1 and 2 is 10 pounds
• The producer should expect 1s progeny to differ
  on average by 10 pounds more than 2s progeny

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Expected Progeny Difference- Example -(in
reference to previous text)
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EPDs Growth Traits

• Growth Trait EPDs predict a calfs ability to
  grow with regard to a specific trait
• Birth weight EPD
• Weaning weight EPD
• Yearling weight EPD

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EPDs Maternal Traits

• Maternal Trait EPDs predict how a sires
  daughter will affect the performance of her calf
• Milk EPD
• Total Maternal EPD
• Calving Ease EPD

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Milk EPD

• Milk EPD evaluates genetic merit for mothering
  ability the expected difference in WWT of
  calves from daughters of a particular sire, due
  to differences in mothering ability
• Sire A 10
• Sire B -5
• Difference 15 pounds

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Total Maternal EPD

• Total Maternal EPD reflects both the milking
  ability transmitted to daughters and direct
  weaning growth transmitted through daughters to
  their calves
• Total ½ WWT EPD Milk EPD
• Predicts total difference in WWT of a calf due to
  growth and milking ability

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Calving Ease EPD

• Calving Ease EPD reflects the ease with which a
  sires progeny is born to heifers or cows
• Direct ease with which calves of a sire are
  born to heifers or cows
• Maternal ease with which a daughters of a sire
  calve as heifers or mature cows

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EPDs Carcass Traits

• Carcass Trait EPDs predict genetic differences
  in carcass merit
• Carcass weight EPD
• Ribeye area EPD
• Fat thickness EPD
• Marbling EPD

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(No Transcript)
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Beef Cattle Performance Targets
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Average Non-Parent EPDs for Calves Born in 1997ab
aNon-parent averages from 1997 or 1998 sire
summaries. bBIF, 1999.
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Genetic Base

• Genetic base is defined as a group of animals
  whose EPDs average zero
• Can be arbitrarily defined
• Can be set by forcing EPD values of animals with
  a certain birth year and breed to average zero
• Can be set by allowing EPD values of base animals
  to average zero

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Genetic Base - Example
Difference between two bulls is 15 pounds
regardless of the base.
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Accuracy (ACC)

• A measure of certainty associated with each EPD
• Accuracy values range from zero (0) to one (1)
• Values closer to 1 indicates a higher level of
  certainty
• Is a reflection of the amount of information
  which has gone into the EPD calculation
  (prediction)

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Accuracy CategoriesMeaning Risk
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Possible Change (PC)

• Given an accuracy value, PC provides a confidence
  range of EPD values in which the true EPDs will
  lie
• A measure of the expected change a producer can
  expect in an individuals EPD values
• An additional way to assess the risk of using a
  particular animal as a parent

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Possible Change Table(Each value is /-)
aFrom Spring 2000 Simmental Sire Summary
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Possible Change Example(in reference to the
previous table)

• If the EPD for WWT is 35 and the ACC value is
  0.20, then the true value for WWT EPD is probably
  between 22 and 48 (35 /- 13)
• The possible change values in the table represent
  one standard deviation. Technically, there is a
  68 chance that the true value for WWT EPD falls
  between 22 and 48.

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The Normal Distribution(Bell Shaped Curve)

• For traits that are normally distributed
• 68 lie in range of /- one standard deviation
• 95 lie in range of /- two standard deviations
• 99 lie in range of /- three standard deviations

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Across Breed EPDs

• EPDs should not be compared across breeds
• Concept of across-breed EPDs was developed in
  late 1980s
• Data from Germ Plasm Evaluation (GPE) at the US
  Meat Animal Research Center (MARC) have been used
  to compute across-breed adjustment factors

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Across Breed EPDs -- Uses

• Commercial producers, utilizing crossbreeding,
  can compare bulls of one breed to those of
  another breed which provides an additional tool
  to achieve breeding goals
• Compare bulls of different breeds being used for
  similar purposes (milk production, calving ease)
• Manage uniformity when rotating breeds
• Note AB-EPDs have no associated accuracies

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2000 Across Breed EPD Adjustment Factors
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Across Breed EPD Adjustment Example 1(in
reference to the previous table)

• To calculate across-breed EPDs, simply add the
  adjustment factor found in the table to the
  existing within-breed EPD for the animals of
  interest
• Example WWT EPD Consider a Simmental with a
  35 WWT EPD and a Charolais with a 15 WWT EPD
• Simmental (35 25.4) 60.4 Across-breed WWT
  EPD
• Charolais (15 44.8) 59.8 Across-breed WWT
  EPD

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Across Breed EPD Adjustment Example 2(in
reference to the previous table)

• To calculate across-breed EPDs, simply add the
  adjustment factor found in the table to the
  existing within-breed EPD for the animals of
  interest
• Example YWT EPD Consider a Limousin with a
  50 YWT EPD and a Charolais with a 50 WWT EPD
• Limousin (50 34.6) 84.6 Across-breed WWT
  EPD
• Charolais (50 73.4) 123.4 Across-breed WWT
  EPD

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Expected Progeny Differences (EPDs)

• EPDs are a measure of an individuals value as a
  parent
• EPDs must be used in a comparison situation
  because the predict differences and not
  performance
• EPDs have associated accuracy and possible change
  values

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Expected Progeny Differences (EPDs)

• EPDs are a powerful selection tool available to
  producers
• EPDs allow fair comparisons of future progeny
  performance for bulls of the same breed
• EPDs add predictability to the genetics of a
  producers cattle