Author
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Kuhn, Melvin |
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Hutchison, Jana |
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Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/25/2008 Publication Date: 6/1/2008 Citation: Kuhn, M.T., Hutchison, J.L. 2008. Prediction of dairy bull fertility from field data: Use of multiple services and identification and utilization of factors affecting bull fertility. Journal of Dairy Science. 91(6):2481-2492. Interpretive Summary: The objectives of this research were to assess the use of multiple services, rather than first service only, and use the factors related to bull fertility for improved prediction of bull conception rate. Accuracy of bull fertility evaluation was improved by a minimum of 20% using the methods tested. These results provide an improved tool for dairy farmers and the artificial insemination industry in their quest to enhance conception rate of U.S. dairy cattle. Technical Abstract: The objectives of this research were to assess the utility of using multiple services, rather than first service only, and an expanded service sire term for prediction of bull conception rate (CR) in the US. The intent with the expanded service sire term was to determine if accuracy could be improved by estimating factors affecting the bull's CR explicitly in the model and then formulating the bull's prediction as the sum of his own service sire solution along with the solutions for the other factors. Factors considered for the expanded service term included age of the bull at the time of mating, stud, inbreeding of the service sire, inbreeding of the mating (potential embryo), and an additive genetic effect. Both simulated and field data were utilized to study the objectives. In simulation, predictions were compared to true values while with real data, predictions were compared to bulls' average CR in set aside data. Field data included 3,312,998 breedings for 737,626 Holstein cows in 1,419 herds distributed over 43 states and across 12 years (1995 to 2006). The use of both multiple services and an expanded service sire term improved accuracy of predictions. Multiple services contributed a 7 to 9% increase in accuracy while the expanded service sire term improved accuracy by an estimated 12%. The amount of improvement in accuracy depends on the number of services available for the bull but even for bulls with at least 500 matings, the combination of multiple services and an expanded service sire term can be expected to result in an overall increase in accuracy of at least 20%. Mean differences between predictions and bulls' average CR in set aside data indicated that this improvement in accuracy can be brought about without introducing bias into the evaluations. Heritability estimates were essentially zero. Thus, use of an additive genetic effect for the service sire will not be of assistance in prediction of bull fertility. All 4 of the other factors used in the expanded service sire term contributed to improved accuracy, although age of bull at the time of mating was, by far, the major factor. Allowing the stud effect to vary by year and using only the stud's most recent year solution in prediction was shown to be superior to using just stud alone; i.e., than assuming stud effects were constant over time. Furthermore, exclusion of stud*year from predictions reduced accuracy by about 6%. |
