Abstract
Two methods for estimation of genetic change are discussed, namely; 1. (1) Comparison of contemporary progenies by sires of two different generations. 2. (2) Comparison of change over time in population mean and performance of successive groups of progeny of individual sires. The pattern of bull usage in modern dairy cattle breeding provides a basis for estimation of genetic change according to either of the two methods, if the data are appropriately adjusted for the effect of selection of bulls on basis of their early progeny. Further, after a slight modification of method 2, the two methods lead to the same mathematical expression. Method 1 has been applied to a set of data from the Norwegian Red breed (NRF). Correction for the effect of selection on basis of the expected repeatability of the progeny test led to an estimate of genetic change of 33 kg FCM per year. However, when the observed regression of subsequent daughters on previous progeny test was used as basis for correction this estimate was reduced to 20 kg FCM.
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