Relationship of maternal milk expected progeny differences to actual milk yield and calf weaning weight.

Calf weaning weights and estimates of 205-d milk yield (n = 317) were obtained from 90 Polled Hereford (PH) and 80 Simmental (SM) cows to evaluate the relationship of these measures with maternal milk and total maternal EPD from national cattle evaluations. An inverse parabolic exponential function predicted 205-d milk yields for each cow from five estimates of daily milk yield taken once per month via calf weigh-suckle-weigh. Changes in calves' 205-d adjusted weights were greater than predicted (P < .02) by maternal milk EPD of PH and SM dams and PH maternal grandsires (MGS) but were similar to changes predicted by SM MGS (P > .50). These changes were also greater than those predicted by total maternal EPD of PH dams and MGS (P < .02) but were similar to those predicted in SM dams and MGS (P > .38). Interactions of maternal milk and total maternal EPD with sex of calf and year did not influence calves' 205-d adjusted weights (P > .10). A positive relationship was found in both breeds between 205-d milk yield EPD (calculated from 205-d milk yield estimates) and maternal milk EPD from national cattle evaluations. Objectively assessing the magnitude of this relationship was hindered by problems in estimating heritability and interpreting correlations between EPD. These data indicate that maternal milk and total maternal EPD from national cattle evaluations are reasonably good predictors of genetic differences in milk yield and weaning weight.