J. Dairy Sci. 86:3366–3373 American Dairy Science Association, 2003. Implementation of a Sire-Maternal Grandsire Model for Evaluation of Calving Ease in the United States

The objective of this study was to add a maternal grandsire (MGS) effect to the existing sire model for national calving ease genetic evaluations. The Animal Improvement Programs Laboratory (AIPL) of USDA assumed responsibility for conducting the national ge-netic evaluation for calving ease and maintaining the associated database in 1999. Existing evaluations used a sire threshold model. Adding an MGS effect to the model was expected to improve accuracy by partially accounting for merit of mates and differences in mater-nal ability of the dams. Dystocia data were migrated to a relational database integrated with the AIPL pro-duction database. This database design allowed more rigorous data edits by comparison with the production data and improved MGS identification (ID) rate by uti-lizing pedigrees from the production records. Integra-tion of dystocia data with production data increased MGS ID rate from 58 to 73%. In addition, nearly 200,000 duplicate records were identified using the new edit system. Sire and sire-MGS models were compared using over 10 million observations available for the August 2002 national genetic evaluation. The sire model included herd-year, season, sex of calf, parity of dam, birth year group of sire, and sire. For the sire-MGS model, MGS and birth year group of MGS were added, year-seasons rather than seasons were used, and sex of calf and parity of dam were combined into a single interaction effect. Herd-year, sire, and MGS were random effects. Variance components used for the sire model were those previously used in the national evaluation and for the sire-MGS model were estimated in a separate study. Correlations between predicted genetic merits for service sire calving ease from the twomodels was 85%, indicating general agreement, but with some significant differences in evaluations. A sire