LongevityWhat should we be selecting for Presented at the World Dairy Expo Educational Seminar Octob

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LongevityWhat should we be selecting
for?Presented at the World Dairy Expo
Educational SeminarOctober 2, 2008

• Bennet Cassell
• Virginia Polytechnic Institute and State
  University

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Characteristics of Holsteins born 20 years apart
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Productive Life has changed

• The current definition of Productive life used by
  USDA is months in milk across lifetime,
  regardless of DIM per lactation
• Each month in production receives different
  weight, depending on milk produced
• Early months in lactation get the most weight
• Later months in extended lactation get the least
  weight
• Cows get high productive life by
• Surviving to have another calf
• Calving on shorter calving intervals

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Phenotypic trends in Holstein, Jersey, and Brown
Swiss cattle
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Genetic trends for productive life in Holstein,
Jersey, and Brown Swiss breeds
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Predicting productive life with combinations of
traits available in the early 1990s
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Sire evaluations for fitness traits

• Productive life available since 1994, redefined
  in 2006
• Somatic cell score available since 1994
• Daughter pregnancy rate new in 2003
• Sire calving ease around since 1978, revised in
  2003
• Daughter calving ease new in 2003
• Sire stillbirth new in 2006
• Daughter stillbirth new in 2006

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Some genetic correlations that affect breeding
programs for lifetime profit
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Components of Net Merit
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How heritability affects Reliability of progeny
tests
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Conclusions about selection for low heritability
traits

• Accurate genetic evaluations PTAs on AI bulls -
  are possible for lowly heritable traits, but only
  after many daughters are available
• Producers should use the information available on
  these traits when bulls are young, despite lower
  Reliability than for more highly heritable traits
• Dont ignore genetic evaluations on traits with
  lower heritabilities. The Reliabilities involved
  are usually 55 to 65 - not zero!
• Base breeding plans on average merit for indexes
  like Net Merit for a group of AI bulls and dont
  be concerned/surprised when some proofs go up or
  down