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Genetic Evaluations for Birth Weight: Comparison of Continuous and Discrete Definitions of Birth Weight

This study compares the accuracy of continuous and discrete definitions of birth weight in genetic evaluations. The study examines varying accuracies of recording birth weight and their impact on heritabilities and genetic correlations. The findings suggest that the manipulation of documentation accuracy and subsuming into discrete variables lead to decreased heritabilities, but estimated breeding values remain robust.

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Genetic Evaluations for Birth Weight: Comparison of Continuous and Discrete Definitions of Birth Weight

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  1. Genetic evaluations for birth weight: comparison of continuous and discrete definitions of birth weight under varying accuracies of recording Waurich1), B., Wensch-Dorendorf1), M., Cole, J.B. 2) and Swalve, H.H. 1) 62th Annual Meeting of the European Federation of Animal Science Stavanger, Norway August 29th-September 2nd, 2011. Session 36, Paper 2 • 1Group Animal Breeding, University of Halle, Theodor-Lieser-Str.11, D-016120 Halle/Saale Germany, • 2Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD, USA.

  2. Introduction • many countries have calving problems • birth weight is highly heritable and strongly connected with dystocia • documentation of birth weight takes economic efforts  weighing or scoring?

  3. Introduction • Data from Mecklenburg-Western Pomerania cooperator test herd scheme with precise documentation ( 22 herds from 2005 ) • Documentation for all calvings of a herd (also stillborn) • Weighing of all calves • heifers (41±4,5kg) and cows (45±5,2kg)

  4. The Idea For birth weight parameter estimation: weighing necessary or subjective scoring precise enough ? frame birth weight muscle mass Weighing data: For research purposes  manipulation of data  grouping weights into in classes

  5. Manipulation of weight data - varying accuracies A Birth weight B +RANUNI(-1,0,1) C +RANUNI(-1,0,1) +RANUNI(-1,0,1) D + N(0,1.5) E + N(0,2)

  6. Calf size - The discrete definitions Continuous Birth weight Five Classes, each about 20 Percent of weighings verylight light medium heavy very heavy Birth weightThresholds 39 42 44 48 Three Classes equal, each about 33 Percent of weighings light medium heavy 41 45 Three Classes wide, thresholds 25, 75 Percent of weighings light medium heavy 40 47

  7. Outcome of class allocations

  8. Model • yijklmno = µ + Hi + YSj + PARk + SEXl + sirem + mgsn + eo Calculation of genetic parameters Calculation of maternal breeding value

  9. Heritabilities and genetic correlations maternal Genetic correlations range between -0.02 and 0.15

  10. Rank correlations of EBVswith undistorted original birth weight

  11. Conclusions • - birth weight heritability is situated mainly on calf side • - manipulation of documentation accuracy leads to reduced heritabilities • - subsumming into discrete variables leads to decreased heritabilities  decrease is far not as strong as expected  estimated breeding values stay robust • This study may not be a perfect imitation of the outcome of a subjective • scoring system (where farmers may describe weights inaccurately), but some • assessment of such a system is given

  12. End

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