RANKING SIRES FOR CALVING EASE

Field records from the American Simmental Association were used to study the relationship between sire expected progeny differences (EPD) for calving ease score and birth weight. Dependent variables in the mixed model, least-squares analyses were calving ease score (1-4) and birth weight. Data analyzed contained progeny records from 87 sires subdivided into 3 subsets containing 4642, 3383 and 4656 records for 2 yr old, 3 yr old and mature dams, respectively. Independent variables were managment unit, sire, sex and percentage Simmental. Each age of dam group was analyzed separately, then all groups were combined in a single analysis. Sire EPD were calculated by regressing the sire constants. Sire was a significant source of variation for calving ease score in 2 yr old and mature dams. Birth weight was significantly affected by sire in all analyses. Correlations of sire EPD for calving ease in 2 yr old with 3 yr old and mature dams were 0.32 and 0.04, respectively, when all sires were considered. When the correlations included only sires with 20 or more progeny, these correlations were 0.46 and 0.21. The correlation of calving ease score with birth weight was 0.53, 0.41 and 0.33 for 2 yr old, 3 yr old and mature dams, respectively.