Abstract
Data on part production records of first lactation of 259 Sahiwal cows maintained at the Livestock Production Research Institute, Bahadurnagar (Okara), during 1979-89 were collected and analysed. The relative efficiency of selection based on 61-90 days milk yield or first 90 days cumulative yield was high i,e, 1.211 and 1.278 as compared to that of selection using total lactation milk yield. Thus the selection of cows can be made earlier, after third month of lactation
