Abstract
Improving lifetime milk yield through the early identification of superior replacement animals is a key objective of sustainable dairy production systems. This study investigated the potential of first-lactation performance indicators to predict lifetime milk yield in dairy cattle managed under subtropical conditions. Historical production records from 349 Holstein, Jersey and crossbred dairy cows maintained at a commercial dairy farm were analysed using linear mixed models, multiple regression and receiver operating characteristic analysis. Estimated lifetime milk yield (ELMY) was calculated from average daily milk yield and lactation length across recorded lactations. Breed, parity, and their interaction significantly influenced several milk production traits (P 4-P5) for selected traits. First-lactation daily milk yield (FDMY) was strongly associated with ELMY (r = 0.849, P P < 0.001), with an overall classification accuracy of 90.6%. Receiver operating characteristic analysis demonstrated excellent discriminatory ability of FDMY (AUC = 0.917 ± 0.036, P < 0.001), with an optimal threshold of 16.0 kg/day providing 76.2% sensitivity and 93.7% specificity. These findings identify first-lactation milk yield as a promising early-life indicator of subsequent estimated lifetime milk yield.