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Genetic evaluation of an index of birth weight and yearling weight

Genetic evaluation of an index of birth weight and yearling weight. Michael MacNeil USDA Agricultural Research Service Miles City, Montana. I = yearling weight - 3.2(birth weight) Proposed by Dickerson et al. (1974). Objectives.

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Genetic evaluation of an index of birth weight and yearling weight

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  1. Genetic evaluation of an index of birth weight and yearling weight Michael MacNeil USDA Agricultural Research Service Miles City, Montana

  2. I = yearling weight - 3.2(birth weight) Proposed by Dickerson et al. (1974)

  3. Objectives • Estimate genetic parameters for birth, weaning, yearling, and mature weights of CGC • Evaluate genetic responses resulting from selection based on the index

  4. Selection Lines • Established in 1989 • Control line (n = 912) • Index line (n = 950) • Generation intervals • Control line 3.90  0.08 yr • Index line 3.16  0.04 yr • 3 generations • 212 kg selection differential

  5. CGC population • Stabilized composite of ½ Red Angus, ¼ Charolais, and ¼ Tarentaise

  6. Phenotypes • Birth weight (n = 5,083) • 200-d weight (n = 4,902) • 365-d weight & index (n = 4,626) • Cow weight (n = 1,433; 4,375 obs)

  7. Derivative-free multiple-trait REML • Calf traits • fixed contemporary groups • random direct & maternal additive effects • uncorrelated random maternal permanent environmental effects • Cow weight • fixed contemporary group effects, • random direct additive effects, • uncorrelated random permanent environmental effects

  8. Three Sets of Analyses • a single-trait analysis of the index • four 2-trait analyses of the index with birth weight, 200-d weight, 365-d weight, and cow weight • three 2-trait analyses of 365-d weight with birth weight, 200-d weight, and cow weight.

  9. Heritability Estimates

  10. Genetic Trends for the Index

  11. Genetic Trends for Birth Weight

  12. Genetic Trends for 365-d Weight

  13. Genetic Trends for 200-d Weight

  14. Genetic Trends for Cow Weight

  15. Relationship of Index to Weight Traits& Response Versus to Selection for 365-d wt

  16. Implications • Despite a genetic antagonism that compromises selection response for reduced birth weight and increased postnatal growth, favorable genetic responses can be achieved. • Selection for the index favorably affected the shape of the growth curve, restricting response in birth weight and mature weight of cows. • Selection intensity in experiment was reduced relative to that which would be available across a breed using national cattle evaluation and AI.

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