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Comparing Models for Cow Fertility and Traits in a Population Simulation

Explore the definition of traits and comparison of models for cow fertility using a simulation of 500 sires and 10-1000 daughters. Analyze data including days open, lactation pregnancy rate, and 21-day pregnancy rate. Learn about the theoretical distribution of days open pregnancy rate and the advantages of using these models for assessing herd fertility. Discover the impact of pregnancy rate on yield and expenses, as well as the relative values of calving ease and fertility traits. Understand the current and proposed selection indexes for yield, health, conformation, and management traits. Conclude with insights on the accuracy, heritability, and economic value of cow fertility traits. Thanks to Tony Seykora (U. Minnesota) and Bob Miller (AIPL) for their contributions, as well as other experts involved in this research.

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Comparing Models for Cow Fertility and Traits in a Population Simulation

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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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