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Potential consequences of selection on gestation length on Holstein performance

Potential consequences of selection on gestation length on Holstein performance. Introduction. Gestation length (GL) genetic evaluations were recently calculated (Norman et. al., 2009) Although GL can be changed genetically, the preferred direction is not clear

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Potential consequences of selection on gestation length on Holstein performance

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  1. Potential consequences of selection on gestation length on Holstein performance

  2. Introduction • Gestation length (GL) genetic evaluations were recently calculated (Norman et. al., 2009) • Although GL can be changed genetically, the preferred direction is not clear • Selection for GL could have economic indirect effects through correlations with cow or calf health and longevity

  3. Objectives • Determine if genetic evaluations of GL were accurate and repeatable • To assess the consequences of changing GL on subsequent milk and fitness traits

  4. Data and methods • Predictor data: • PTA GL derived from calvings between Jan. 1998 and Dec. 2005 • Stratify bulls into 7 groups (<-3.00, -3.00 to -2.01, -2.00 to 1.01, … 1.00 to 1.99, and ≥2.00) according to PTA GL • Predictee data: • First parity phenotypic data of cows calving Jan. 2006 through Nov. 2009 mated to same bulls

  5. Model to examine effectiveness of PTA GL Phenotypic trait= Herd-yr of conception + Service sire PTA GL group + cow conception day + cow conception day squared + error

  6. GL (days) Milk (kg) Fat (kg) Protein (kg) SCS Productive Life Days Open Calving Ease score Stillbirth (%) Culled (%) Traits predicted:

  7. Least squares means for gestation length

  8. Least squares means for production traits

  9. Least squares means for fitness traits

  10. Model to examine GL effect on subsequent lactation (phenotypic) 2nd parity trait= Herd-yr of conception + Cow 1st parity gestation length group + cow conception day + cow conception day squared + error

  11. Least squares means for 2nd parity production traits

  12. Least squares means for 2nd parity fitness traits

  13. Conclusions • Gestation length can be changed through choice of service sire • Relationship between GL and subsequent performance was small • Little evidence found that shortening or increasing GL would provide an advantage overall

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