Historical perspectives on genetic fitness research

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Historical perspectives on genetic fitness
research
ADSA Pioneer
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Fitness (Dictionary.com)

• The state or condition for being fit suitability
  or appropriateness
• Good health or physical condition
• The extent to which an organism is adapted to or
  able to produce offspring in a particular
  environment

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Common understandingof fitness traits

• Nonproduction
• Functional
• But what makes a dairy cow more fit and
  functional than production?
• We may strain the dictionary definition, but we
  know what we mean

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Conformationor type

• Anecdotal observations for eons
• What we thought cow should look like
• Linear scoring began around 1980
• Promoted research on real value of type traits

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Longevity

• Justification for type emphasis
• Direct observation
• Indicator traits

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Somatic cell/mastitis

• SCS is convenient trait for selection for reduced
  mastitis
• Clear importance and relatively ready acceptance
  of research
• Like yield, obvious milking-to-milking impact on
  income (profit)

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Fertility

• Should we have foreseen problems?
• Some natural selection
• Tribolium pupa weight study (1976)
• Negative response in family size
• Eventual extinction by generation 16

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Calving ease

• Giving birth is most traumatic time in a cows
  life
• Can minimize negatives by reducing calvings or by
  mating plan
• Better yet, reduce frequency of bad genes
  (daughter calving ease)

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Genetic evaluations
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Indexes

• Consider all traits with a single number
• Vital with so many traits
• Needs to be appropriate for market
• Needs to be reasonably accurate
• Many correlated traits complicate process

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History of USDA indexes

• Traits Year
• Milk, fat 1971
• Protein, solids-not fat 1976
• Productive life, somatic cell score 1994
• Type composites 2000
• Daughter pregnancy rate, 2003
• calving ease
• Stillbirths 2006

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Deleterious genes

• Mulefoot
• Bovine leukocyte adhesion deficiency (BLAD)
• Uridine monophosphate synthase deficiency (DUMPS)
• Complex vertebral malformation (CVM)
• Weaver
• Limber leg
• Rectovaginal constriction (RVC)

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Learning from history

• Obsession with production
• Low heritability vs. no heritability
• High economic value
• Large variation
• Breed for yield, cull for function
• We got what we asked for

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Learning from history (cont.)

• Beware of pendulum swinging too far back
• Theoretically, index weights based on research ?
  correct index ? optimum progress