nuts and bolts of genetic improvement genetic model predicting genetic levels increase commercial...

Nuts and Bolts of Genetic Improvement

Genetic ModelPredicting Genetic Levels

Increase Commercial Profitability

Lauren Hyde

Jackie Atkins

Wade Shafer

Fall Focus, Gettysburg, PA Sept. 14th, 2015

Punnett Square

Qualitative Traits

• Controlled by one or few pairs of genes• Measured on a categorical (either-or) scale• Examples

– Black or red– Polled or horned– Genetic defects

• Genotype determined through DNA testing

Genetic defects?

Quantitative Traits

• Controlled by many genes• Measured on a continuous scale• Examples

– Weaning weight (lb)– Ribeye area (sq in)

• Transmittable part of genotype determined through statistical techniques (and DNA testing)– EPD = ½ * EBV

Genetic Model

• Phenotype = Genotype + Environment• Phenotype is the observed level of

performance• Genotype is the genetic makeup of the animal• Environment is the effect that non-genetic

factors have on performance

Genetic Predictions (EPDs)

• Separate genetics from environment– Nature vs nurture

• Estimated using highly advanced statistical methods– BLUP– System of linear equations– Solve for x and y if 2x + 3y = 6 and 4x + 9y = 15

Mixed Model Equations

Heritability

• Heritability - the proportion of phenotypic variation for a specific trait in a specific population that is due to transmissible genetic merit

• Ranges from 0 to 1– h2

CE = 0.19

– h2BW = 0.38

– h2REA = 0.46

Heritability

• The higher the heritability of a trait, the more accurately an individual’s own performance predicts genetic merit

• Even with high heritability we are limited in what we can learn about an animal’s true breeding value from its phenotype

Data

• Large amounts of performance data are the solution– Animal’s own performance– Progeny performance– Performance of ancestors and other relatives

• Progeny performance records are the most influential

Data Collection

• Accurate pedigree records• Performance records for as many traits as

possible on complete contemporary groups– Performance Advocate

Contemporary Group

• Same sex• Close in age (within 90 days)• Raised in same management group from birth

– Same pasture– Same feed

Contemporary Group

• Should include as many cattle as can be compared accurately

• But only takes two

Contemporary Group ExampleAnimal ID Weaning Weight (lb)

2142 801

2134 783

2135 756

2147 729

2139 671


2142 801

2134 783

2135 756

2147 729

2139 671

• Average WW = 748 lb• 2142’s WW ratio = 107.1


2142 801

2134 783

2135 756

2147 729

2139 671

Contemporary Group Example

• What happens when 2142 starts getting used in other herds?

Contemporary Group Example

• Progeny data will get his EPDs going in the right direction

• Faulty data will get washed away• BLUP is very robust

Sire Summary

Interpretation

• 35R– BW EPD = -3.0 (.64)

• 3C Full Figures C288 BLK– BW EPD = -0.7 (.96)

• Difference– -3.0 – (-0.7) = -2.3– We would expect 35R’s progeny to weigh -2.3

pounds less at birth on average than 3C Full Figures C288 BLK’s

Accuracy

• Measure of the strength of the relationship between the true breeding value and its prediction

• Range from 0 to 1• Affected by the number of progeny records• Higher values associated with less risk and

lower values with more

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