Sire marbling score expected progeny difference and weaning weight maternal expected progeny difference associations with age at first calving and calving interval in angus beef cattle

Field records from the American Angus Association were used to study the as sociations of sire marbling score EPD and sire weaning weight maternal (mil k) EPD with age at first calving (AFC) and calving interval (CI). Cows were selected based on the accuracy of their sire's milk (greater than or equal to.7) or marbling (greater than or equal to.6) EPD, The data were screened using biological constraints, and regression models were used to identify records that were greater than 5 SD from the mean. The AFC was modeled for both milk and marbling data sets to account for effects of year, sire EPD, and their interaction. The CI was subdivided into first, second, and mature calving interval traits and modeled to account for state, year, calf sex, calf birth weight (BW), calf weaning weight (WW), sire EPD, and interaction s of EPD with year and state. Derivative-free REML was used to estimate her itability and genetic correlations for AFC and CI. Sire milk EPD and marbli ng EPD were predictors of AFC (P<.001); however, pooled estimates were unre liable because of state x EPD interactions (P<.001). Increases in sire milk EPD resulted in reductions in AFC; however, there was no consistent patter n to effects of marbling EPD increases. Models accounted for <8% of variati on in AFC, Sire milk EPD was not a predictor of first, second, or mature CI (P>.1). Sire marbling score EPD was not a predictor of second, or mature C I (P>.1); however, it was associated (P=.059)with first CI, although regres sion estimates varied across states and prevented pooling. The BW, sex, and WW were predictors of CI (P<.001). Increases in BW resulted in longer matu re CI, and mature CI decreased as WW increased. The AFC was heritable (.22) , and CI traits had heritabilities ranging from .01 to .03. The AFC was gen etically correlated with first CI (-.6) and mature CI (-.93), Genetic corre lations between CI traits were uninterpretable because of low additive gene tic variances. In conclusion, sire marbling score and milk EPD do not seem to be reliable predictors of AFC or CI. The BW and WW have significant but small effects on AFC and CI. Selection for AFC is possible, but earlier cal ving heifers may have longer calving intervals.