PREDICTION OF 305-DAY LACTATION MILK YIELD BASED ON BIMONTHLY TEST DAY VALUES IN KARAN FRIES CATTLE

The present investigation was carried out using data of first lactation bimonthly (BTDY) test day milk yields and 305-day milk yield records of 1345 Karan Fries cows sired by 84 bulls from 1984-2006 maintained at NDRI, Karnal. The test day milk yields recorded from 6th to 305th day at bimonthly intervals were used to predict 305 day milk. Based on simple linear regression analysis with only one independent variable, the regression coefficients showed a consistently increasing trend up to BTDY-3 and thereafter a consistently declining trend up to BTDY-7 test day milk yield was noticed. The accuracy of prediction (R2) of 305-day milk yield based on individual bimonthly test day milk yields varied between 19% (BTDY-1) and 59% (BTDY-4). However, slightly higher estimates of accuracy of prediction in the middle portion of lactation in bimonthly test day milk yields were observed. The absolute error, percent error and error variance showed continuously declining trend from BTDY-1 to BTDY-3 but then increasing trend from BTDY-3 to BTDY-6. Based on fitting of stepwise multiple regressions, the regression equation with 3 variables viz. BTDY-2, BTDY-3 and BTDY-5 was considered more appropriate for prediction of first lactation 305-day milk yield with 83 % accuracy and 7.54 per cent error of prediction in 305-day milk yield.