Prediction of 305-Day Lactation Milk Yield Based Monthly Test Day Values in Karan Fries Cattle

摘要

The present investigation was carried out using data of first lactation monthly (MTDY) 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 monthly intervals were used to predict 305 day milk. Simple linear regression analysis with only one independent variable at a time and stepwise backward multiple linear regression analysis was used to predict 305-day milk yield. Based on simple linear regression analysis with only one independent variable, the regression coefficients ranged from 83.18 (MTDY-11)to 189.65 (MTDY-5). The regression coefficients showed a consistently increasing trend up to MTDY-4 and thereafter consistently declining trend up to 11th monthly test day milk yield was noticed. The accuracy of prediction (R~2) of 305-day milk yield based on individual monthly test day milk yields varied between 19% (MTDY-1) and 61% (MTDY-6). The absolute error,percent error and error variance showed continuously declining trend in all the monthly test day milk yields. Based on fitting of stepwise multiple regressions, the regression equation with 4 variables viz. MTDY-2, MTDY-4, MTDY-6 and MTDY-9 was considered more appropriate for prediction of first lactation 305-day milk yield with 86% accuracy and 6.79 percent error of prediction in 305-day milk yield.