How Does Additional Information Impact Accuracy? Dan W. Moser Department of Animal Sciences and Industry Kansas 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? BV / t rBV , EBV i BV L 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 CE 1 U 2 U 3 U 4 U 5 U 6 U 7 A 8 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 True Accuracy of Selection for IMF Genetic correlation between IMF and MARB True Accuracy of Selection for Marbling (BIF) Accuracy of Selection for Marbling 0.90 0.50 0.20 0.995 0.866 0.600 0.70 0.70 0.70 0.696 0.606 0.420 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 PHS 10 10 10 200 200 200 h2 .05 .25 .45 .05 .25 .45 No Prog .04 .17 .29 .11 .22 .32 BIF Accuracy 5 50 Prog Prog .07 .24 .25 .54 .38 .65 .13 .28 .29 .55 .44 .66 500 Prog .63 .83 .88 .64 .83 .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.