One of the causes of culling dairy cows is low milk yield and to the extent that this has any genetic basis one might expect the daughters of old cows to outyield their contemporaries from younger and hence less selected mothers. This is quite apart from any confounding effects resulting from the non-genetic influences of dams' parity. The rate of genetic improvement derived from the culling process will be modified within a population by the extent to which farmers choose to retain the progeny of older rather than younger cows. Milk yields for recorded cows in Scotland, available to the Livestock Records Bureau, have been used to obtain some information on these points.