Relationship between a bull's parental genetic merit difference and subsequent progeny trait variability in Angus, Gelbvieh, and Limousin cattle

Data from the American Angus Association, American Gelbvieh Association, and the North American Limousin Foundation were analyzed to determine whether parental genetic differences are associated with Mendelian sampling of their bull progeny or with Mendelian sampling variances and weight variances of their bull progeny's offspring. Parental differences were measured as the difference between the parents' EPD for birth weight (DIF_BW), weaning weight direct (DIF_WW), and yearling weight (DIF_YW). A bull's data were used if both parents had calculated EPD and the bull had at least 25 progeny with records for the specific trait. Traits calculated for each bull were his Mendelian sampling (MS_Bull), progeny Mendelian sampling variance (MSσ²_progeny), progeny weight variance (WTσ²), and progeny corrected weight variance (CWTσ² = adjusted weight minus appropriate dam EPD) for birth, weaning, and yearling weights. Pearson correlations were computed between DIF_BW, DIF_WW, and DIF_YW and MS_Bull, MSσ²_progeny, WTσ², and CWTσ² for each trait, within each breed. Across breeds, the correlations ranged from -.07 to .11 for MS_Bull, .01 to .14 for MSσ²_progeny, -.06 to .09 for WTσ², and -.06 to .08 for CWTσ². Although some of the correlations were significantly different from zero their relatively small magnitude indicates little relationship between parental differences in genetic merit and subsequent offspring variability for each of the three breeds.