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Definition of Traits and Comparison of Models for Cow Fertility

Definition of Traits and Comparison of Models for Cow Fertility . Cow Fertility Simulation. Compare data and models Days open Log of days open Lactation pregnancy rate (1 / n) 21-day pregnancy rate (yes or no) Population simulated 500 sires with 10 – 1000 daughters

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Definition of Traits and Comparison of Models for Cow Fertility

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  1. Definition of Traits and Comparison of Models for Cow Fertility

  2. Cow Fertility Simulation • Compare data and models • Days open • Log of days open • Lactation pregnancy rate (1 / n) • 21-day pregnancy rate (yes or no) • Population simulated • 500 sires with 10 – 1000 daughters • Sire effects normal for days open

  3. Theoretical Distribution ofDays Open

  4. Pregnancy Rate • Rate that cows become pregnant • Can be derived from days open • Non-linear: 21 / (DO – VWP + 11) • Linear approx: (233 – DO) / 4 • Advantages over days open • Positive numbers are desirable • Earlier measure of herd fertility

  5. Pregnancy Rate vs Days Open 100 90 80 70 60 Pregnancy Rate 50 40 30 20 10 1 2 3 4 5 6 7 8 9 0 60 81 102 123 144 165 186 207 228 249 Number of Chances Days Open

  6. Simulation Results • Heritability estimates .040 for days open .035 for log (days open) .029 for lactation pregnancy rate .009 (4) for 21-day pregnancy rate • True accuracy, or corr (EBV, BV) .603 for days open .585 for log (days open) .566 for lactation pregnancy rate .602 for 21-day pregnancy rate

  7. Value of Cow Fertility • Optimum days open • Pregnancy rate affects mean and variance • Reduced yield/day vs longer lactations • Fertility expenses per day open • Heat detection ($20 / lact  .005) = $.10 • Semen ($15 / unit + $5 labor) *.025 = $.50 • Pregnancy exam ($10 / exam)*.012 = $.12 • Lactations too long or short = $.75 • Relative value of DPR = 7% of total

  8. Value of Calving Ease • Daughter CE value / difficult birth • Veterinary, labor costs = $50 • Calf death (20% prob) = $25 • Cow deaths before 1st test (1% prob) = $15 • Service sire CE also includes • Yield losses / lactation = $40 • Fertility and longevity losses = $30 • Relative values of each are 2% of total

  9. Current and Proposed Selection Indexes:Yield and Health Traits

  10. Current and Proposed Selection Indexes:Conformation and Management Traits

  11. Conclusions • Days open is right skewed but was more accurate and heritable than log or reciprocal transformations • 21-day pregnancy rate had equal accuracy due to more observations but lower heritability per observation • In NM$, cow fertility will receive 7% and calving ease traits each will receive 2% of total selection

  12. Thank You • Tony Seykora (U. Minnesota) and Bob Miller (AIPL) helped derive an economic value for cow fertility • Many others contributed to the revision of Net Merit: • Jack Dekkers, Duane Norman, Melvin Kuhn, Les Hansen, Kent Weigel, Gary Rogers, Steve Schnell, Cheryl Marti, Bennet Cassell, George Shook

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