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Use of early lactation days open records for genetic evaluation of cow fertility

This study explores the use of early lactation days open (DO) records for genetic evaluation of cow fertility. The predictor equation includes lactation, calving ease, age, days open based on last breeding, and milk yield. The results show that records can begin to be used at 130 DIM, leading to a reduction of 4 months in the evaluation of cow fertility.

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Use of early lactation days open records for genetic evaluation of cow fertility

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  1. Use of early lactation days open records for genetic evaluation of cow fertility M.T. Kuhn* and P. M. VanRaden USDA-AIPL, Beltsville, MD

  2. Introduction • - National genetic evaluation for female fertility introduced in February, 2003 • - Evaluations are based on Days Open (DO) • - Current requirement: • Records must be a minimum of 250 days in milk

  3. Reason for 250 DIM Requirement • - Avoid potential bias • - Sires poor for fertility: • - Only best daughters available early in • lactation •  upward bias for poor sires

  4. Consequence of 250 requirement: • - Young bulls: • - First proof for yield 40 days after • daughters initiate first lactation • - Must wait 7 more months for DPR • evaluation

  5. Objectives • - Develop a predictor for DO • - Determine how early in lactation it can be used

  6. Prediction Equation • ŷ = Intercept + • Lactation + • Calving Ease (CE) + • ß1*Age + ß2*Age2 + • ß3*Milk + ß4*Milk2 + • ß5*(DO based on last breeding) - Models without milk yield also examined

  7. Prediction Equation • - Model is fit separately for each of 9 DIM groups: • 70, 90, 110, 130, 150, 170, 190, 210, 230 Define: DO70 = DO based on breedings up to 70 DIM DO90 = DO based on breedings up to 90 DIM . . . . . . DO230 = DO based on breedings up to 230 DIM

  8. Evaluation of the Predictor • - Bias: Compare ŷ vs y • - Cor(ŷ, y) • - Phenotypic • - Genetic • - Compare: PTAŷ and PTAy

  9. 3 main things to do: 1) Estimate effects in prediction model, solutions to be used to calculate ŷ’s • DATA • - Breeding records from 4 DRPCs • - Years available: 1995-1999 • - Date of breeding, service sire, service number • recorded for each service on each cow-lactation 2) Estimate genetic correlations 3) Calculate PTAs: PTAy vs PTAŷ

  10. Estimation of Genetic Correlations • - Vars/Covs estimated using REML • - Model for estimation: • y = HYSP + Sire + e • - 11 traits: • Actual DO, DO70, DO90, …, DO230, Milk • - Data from 1995-1998 •   670,000 records, 1000 sires

  11. Comparing PTAs • - Data from 1995-1998 •  375,000 records • - Only 1998 records were predicted •  127,000 predicted records • - Animal model for calculation of PTAs: • y = HYSP + A + PE + e

  12. RESULTSPercentage of cows with a breeding by DIM • Days Percent Cumulative % • 70 36 36 • 90 25 61 • 110 15 76 • 130 9 85 • 150 5 90 • 170 3 93 • . . . • . . . • . . . • > 250 1.4 100

  13. Phenotypic Comparisons • Trait Mean Cor • Actual 138.8 1 • DO70 138.7 .28 • DO90 138.1 .36 • DO110 137.8 .44 • DO130 137.9 .54 • DO150 138.1 .63 • DO170 138.3 .71 • DO190 138.4 .78 • DO210 138.5 .83 • DO230 138.5 .88

  14. Genetic Correlations of Predicted and Actual DO • Prediction Model • Day W/ Milk No Milk Mix • 70 .73 .73 .74 • 90 .80 .80 .80 • 110 .85 .86 .86 • 130 .90 .91 .91 • 150 .94 .94 .94 • 170 .96 .97 .97 • 190 .98 .98 .98 • 210 .99 .99 .99 • 230 .99 .99 .99

  15. Genetic Correlations of Predicted DO with Milk • Prediction Model • DayW/ Milk No Milk Mix • 70 .42 .29 .36 • 90 .44 .33 .36 • 110 .45 .35 .36 • 130 .45 .36 .36 • 150 .42 .35 .35 • 170 .39 .34 .34 • 190 .38 .33 .33 • 210 .35 .32 .32 • 230 .34 .31 .31 Gen Cor of milk with Actual DO = .31

  16. w/ Milk in ŷ for all records Milk if no brdg, No milk, o.w. Cow PTAs Based on Actual vs Predicted Records • Mean* • DIM PTAŷ-PTAy Corr • 110 -.06 .90 • 130 -.007 .92 • 150 .01 .93 • 110 -.10 .90 • 130 -.04 .91 • 150 -.01 .93 • *Expressed in standard deviation units

  17. Sire PTAs Based on Actual vs Predicted Records1 • Mean2 Corr Rank • DIM PTAŷ-PTAy (PTAŷ, PTAy) Corr • 110 -.06 .93 .92 • 130 -.008 .94 .93 • 150 .02 .95 .94 • 1 Predictor included milk if no breeding, no milk if with breeding • 2 Expressed in standard deviation units

  18. Conclusions • 1. Projection of DO records will utilize: • - Lactation • - Calving ease score • - Age • - DO based on last breeding • - Milk yield, if no breeding • 2. Records can begin to be used at 130 DIM •  Reduction of 4 months

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