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Understanding USDA Genetic Evaluations for Livestock Type Traits

The USDA conducts genetic evaluations to assess type traits in livestock, detailing the physical characteristics of animals. Final scores range from 50-99, indicating the overall assessment, while linear traits are evaluated on a scale of 1-50. Historical evaluations have evolved since 1986, integrating various models to enhance genetic predictions. Genetic correlations influence the evaluation of traits and heritability measures the genetic contribution to variation. The Production-Type Index (PTI) combines yield and type evaluations, reflecting genetic progress over the years.

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Understanding USDA Genetic Evaluations for Livestock Type Traits

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  1. USDA Genetic Evaluations for Type Traits

  2. Type Traits • Describe physical characteristics of animal • Final Score (overall assessment) • Scored  50-99 • Linear traits (13 traits) • Scored 1-50

  3. History of Type Evaluations • 1986 – Sire model for final score • 1988 – Collection of linear traits • 1989 – Sire model for linear traits • 1995 – Multi-trait animal model • 2000 – Base change • 2005 – Base change

  4. Numbers of Appraisals of Does

  5. Appraisals for Does in 2005(n=4,593)

  6. Evaluation model • An equation that indicates what factors contribute to an observation • Separates the genetic component from other factors • Solutions used to predict the genetic potential of progeny

  7. Type Evaluation Model MODEL: y = h + a + p + e y = Adjusted type record h = Herd appraisal date a = Animal genetic effect (breeding value) p = Permanent environment Non-genetic effect common to all a doe's appraisals e = Unexplained residual

  8. Multi-trait Model • Scores from one trait affect the evaluation of other traits through the genetic correlations

  9. Genetic Correlations

  10. Genetic Parameters • Heritability – Portion of variation due to genetics • Repeatability – Similarity of repeated records, includes genetic and permanent environmental effects

  11. Heritability and Repeatability

  12. Genetic Change per year from does born 1990 – 2003

  13. Breeding value trend for type

  14. Herds for Bucks Born 1999 – 2003(n=2,451)

  15. Daughters for Bucks Born 1999 – 2003(n=2,451)

  16. Distribution of Reliability for Final Score

  17. Methods of Expressing evaluations • Estimated breeding value (EBV) • Animal’s own genetic value • Predicted transmitting ability (PTA) • ½ EBV • Expected contribution to progeny

  18. Combining type and production Production-Type index (PTI) • Combines yield and type evaluations into a single value • There are 2 versions: • PTI 2:1, weights 2 production : 1 type • PTI 1:2, weights 2 type : 1 production

  19. AIPL web services http://aipl.arsusda.gov/query/public/tdb.shtml#GoatsTBL • Queries provide display of: • Pedigree information • Yield records • Herd test characteristics • Genetic evaluations of does & bucks • Yield • Type • Access information using: • ID number • Animal name • Herd code

  20. 1918

  21. 1947

  22. 1977

  23. 2003

  24. Summary • Type data contributes to genetic evaluations of Final Score and 13 linear traits • Multi-trait Animal Model combines information from all relatives and traits • Few bucks have many daughters in many herds so reliability is low • Production-type index combines evaluations • Substantial genetic progress is occurring in several traits

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