This thesis aims to (1) quantify the impact of MR feeding levels in calves on carcass composition and (2) to evaluate a mechanistic model’s (SIMON) ability to predict multiple outcomes in diary calves. The calves were fed one of two MR allowances (LOW or MOD) and the carcass composition was analyzed through chemical analy-sis. The results indicate that elevating preweaning milk replacer consumption can increase carcass fat percentage, carcass weight, viscera weight, protein weight, and dry matter and moisture when expressed as a percentage or in weight. The model was evaluated against 5 published studies as well as against the data collected in Chapter 2. The model was excellent at predicting BW and methane production, did well predicting carcass weight and nitrogen retention, and with further development will be a useful tool to evaluate and develop feeding strategies for calves without the use of animal trials.