How DoesAdditional Information

Impact Accuracy?

Dan W. MoserDepartment of Animal Sciences and

IndustryKansas State University, Manhattan

http://www.asi.ksu.edu

Additional Information

• Start with a pedigree, possibly a phenotype

• Add:– Phenotype for a correlated indicator trait– Progeny test data– DNA test results

• How much is accuracy of selection increased by adding each piece of additional information?

What Drives Genetic Change?

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irt BVEBVBV

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Bourdon, 2000

What Drives Genetic Change?

• Accuracy of Selection• Generation Interval• Genetic Variation• Intensity of Selection

Rate of Genetic Change

• Additional information

– Should increase accuracy

– May increase generation interval

– May reduce intensity of selection• If only certain animals have additional info

It Often Comes Down To:

• Is the value of the additional information worth the time and cost required to get it?

• Is the additional information available on enough animals to maintain selection intensity?

Correlated Traits

• Birth Weight as a predictor of Calving Ease– Because Calving Ease is a binary trait

(yes/no), having a correlated continuous indicator trait can add considerable accuracy to selection

Correlated Traits

Calf 1 2 3 4 5 6 7 8

CE U U U U U U A A

BW 65 70 75 80 85 90 75 95

CE: U = Unassisted, A = Assisted

Unmeasured ERT

• ERT = Economically relevant trait• When ERT is unmeasured, the

genetic relationship between the ERT and the indicator trait must be strong

• Otherwise accuracy of selection for the ERT using only the indicator is low

Accuracy of Correlated Selection

Acc (ERT selection) = Acc (Indicator EPD)

x rG btw ERT and Indicator

Where Acc is true accuracy, not BIF accuracy

Example: Ultrasound

• Use live-animal ultrasound measurement as an indicator of carcass merit

• Assume genetic correlation btw yearling bull ultrasound and steer carcass is 0.70

• If a bull has an ultrasound EPD with accuracy of 0.90, what is the accuracy of selection for carcass?

Example: Ultrasound

If the 0.90 accuracy is “true” accuracy, then the “true” accuracy of selection is:

0.90 x 0.70 = 0.63

But “BIF” accuracy would be quite different:

BIF Accuracy

(BIF) Accuracy of IMF EPD

0.90 0.50 0.20

True Accuracy of Selection for IMF

0.995 0.866 0.600

Genetic correlation between IMF and MARB

0.70 0.70 0.70

True Accuracy of Selection for Marbling

0.696 0.606 0.420

(BIF) Accuracy of Selection for Marbling

0.282 0.205 0.092

Bottom Line

• BIF accuracy understates the true accuracy of selection

• Selection on indicator traits only is significantly less accurate unless the genetic correlation is very high

Progeny Test

• How much additional accuracy is added by a progeny test, assuming the animal is phenotyped?– Depends on the heritability of the trait– Depends on the number of progeny– Depends (a little) on how much

pedigree information is available on the animal

Progeny Test Example

• BIF accuracy values, calculated from Selection Index

• Individual record on animal• 10 or 200 Paternal half-sibs• 0, 5, 50 or 500 progeny• Heritability of 0.05, 0.25 or 0.45

Progeny Test Example

BIF Accuracy

PHS h2

No Prog

5 Prog

50 Prog

500 Prog

10 .05 .04 .07 .24 .63

10 .25 .17 .25 .54 .83

10 .45 .29 .38 .65 .88

200 .05 .11 .13 .28 .64

200 .25 .22 .29 .55 .83

200 .45 .32 .44 .66 .88

Progeny Test Example

• Progeny data add accuracy, regardless of heritability

• Pedigree adds relatively little accuracy especially when significant numbers of progeny are evaluated

Adding Molecular Information

• Van Eenennaam (2010) showed that if molecular breeding values (MBV) explained all of the genetic variation for a trait, the increase in genetic gain from MAS would be substantial

• No products currently on the market have been shown to explain a majority of the variation for a quantitative trait

Adding Molecular Information

• MacNeil et al. (2010) compared the use of ultrasound measurements and MBV for prediction of carcass marbling BV in Angus cattle

• Genetic correlation between ultrasound IMF and carcass marbling was 0.56, and 0.38 between MBV and carcass marbling

Adding Molecular Information

• Despite the lower genetic correlation, the authors expected greater genetic gain from selection on MBV than on ultrasound, because MBV are fully heritable

• Ultrasound values on sibs provide significantly increased genetic gain, but MBV on sibs does not

Adding Molecular Information

• Authors concluded that a very limited amount of progeny carcass data would be more informative than either MBV or ultrasound

• MBV selection is more useful for traits that are difficult to measure, or that are measured later in life

Summary

• Accuracy of indicator trait EPD does not reflect accuracy of selection for ERT

• Progeny records add significant information, but adds both expense and time to evaluations

• Molecular breeding values could be a very useful tool for selection, if the tests explain larger portions of the variation in a trait.