J. Dairy Sci. 86:1845–1848 American Dairy Science Association, 2003. Calving Ease (Co)Variance Components for a Sire-Maternal Grandsire Threshold Model

Variance components for a sire-maternal grandsire (MGS) threshold model were estimated from subsets of the US calving ease (CE) database, which includes over 10million calving recordswithCE scored 1 (no problem) to 5 (extreme difficulty). Selected records included sire and MGS among the 2601 most frequently appearing bulls. The data were further restricted by requiring at least 20 records in each herd year. Five mutually exclusive sample datasets of approximately 200,000 re-cords each were created based on herd code. The model included random herd-year, sire, MGS, and residual effects and fixed year-season, parity-sex, and birth year of sire and MGS effects. Fewer than 50 iterations were required to reach convergence. The (co)variance compo-nent estimates from the five replicates were quite simi-lar. The set of estimates (0.438, herd-year; 0.022, sire; 0.016, MGS; 0.009, sire-MGS) that yielded among the highest heritabilities (0.086, direct; 0.048, maternal) and a correlation of direct and maternal effects near the mean (−0.12) was selected for use in the implemen-tation of a sire-MGS model for CE. (Key words: calving ease, dystocia, threshold model) Abbreviation key: CE = calving ease, MGS = mater-nal grandsire