Adjustment of a Net Income Function for Opportunity Cost of Postponed Replacement on a Lactation Basis

Opportunity cost of postponed replacement is the income forfeited by keeping a cow an additional lactation and is estimated by the income produced by an average replacement. We studied the effect of refining estimated net income by calculation of an opportunity cost for each lactation. After edits, the data consisted of records for 2,982,001 Holstein cows from herds classified be- tween 1983 and 1992.