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Title:   Author  item
                                            Kuhn, Melvinitem
                                            Vanraden, Paulitem
                                            Hutchison, Jana
  Submitted to: Journal of Dairy Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/20/2004
                                    Publication  Date: 7/1/2004
                                    Citation: Kuhn, M.T., Van Raden, P.M., Hutchison, J.L. 2004. Use of early lactation days open records for genetic evaluation of cow fertility. Journal of Dairy Science. 87(7):2277-2284.Interpretive Summary: National genetic evaluations for cow fertility, reported as daughter pregnancy rate (DPR), were introduced by USDA in February, 2003.  One requirement of the fertility evaluation system is that lactations be at least 250 days in milk to be included for analysis.  This was done to avoid potential bias that could be created by using only cows that were bred early in lactation.  The objective of this research was to develop a predictor of days open, usable in genetic evaluation, to allow for earlier predicted transmitting abilities, especially for young bulls.  Days open can be adequately predicted, for single trait genetic evaluation, at 130 days in milk.  This is a reduction of four months in waiting time for DPR evaluations based on daughter performance.  USDA plans to implement use of predicted days open in DPR evaluations starting November 2003.  The results of this study are important to the dairy industry because an increase in reliability of about 5% can be expected for sires between the ages of 4 and 5 years.
                                Technical Abstract: 	National genetic evaluations for cow fertility were introduced by USDA in February, 2003.  These evaluations, reported as daughter pregnancy rate, are based on days open.  One requirement of the evaluation system is that lactations be at least 250 days in milk (DIM) to be included for analysis.  The objective of this research was to develop a predictor of days open, usable in genetic evaluation, so as to allow for earlier predicted transmitting abilities (PTA), especially for young bulls.  The final prediction equation included an overall intercept, the effects of lactation and calving ease score, the linear and quadratic effects of age at calving, and a regression on days open based on last breeding.  Data used for estimation were breeding records from four dairy records processing centers for the years 1995 through 1998.  Genetic correlations were >= 0.91 by d 130 and phenotypic means of predicted days open were in agreement with means for final days open indicating that the predictions were phenotypically unbiased.  Comparison of mean PTA based on actual and predicted days open indicated no bias in PTA and correlations between PTA were >= 0.92 by d 130.  USDA plans to implement use of predicted days open, for records that are at least 130 DIM, starting November, 2003.  An increase in reliability of about 5% can be expected for sires between the ages of  4 and 5 years.


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