Relationship between milk expected progeny differences of polled Hereford sires and actual milk production of their crossbred daughters.

One hundred sixteen spring-calving Polled Hereford x Angus cows were milked using milking machines after receiving 20 IU of oxytocin. Sires of the cows had been divergently selected on yearling weight (YW) and total maternal (MAT) EPD to form four groups: high YW, high MAT EPD; high YW, low MAT EPD; low YW, high MAT EPD; and low YW, low MAT EPD. Average milk production after 12-h calf separation was 3.7 +/- 1.3 kg. Actual milk production of cows was regressed on their sires' milk EPD, where the milk EPD estimates the additive maternal genetic contribution of a sire to the weaning weight of his daughters' calves. The regression of actual 12-h milk production on sire milk EPD was .038 +/- .014 kg/kg, and the correlation was .26 (P less than .006), close to its expected value, based on the accuracy of the prediction, heritability of the trait, and the relationship between sire and daughter. Extension of results of a single milking to an entire lactation is difficult, but over the range of sire milk EPD sampled (-10 to 16 kg), the range in daughters' milk production predicted from the regression analysis was 27% of the mean actual milk production, corresponding to an increase of about 1% more milk per kilogram of milk EPD.