CalfSim tool: A free and user-friendly decision support tool for designing and simulating optimized feeding plans for dairy calves-A prediction assessment study.

Optimizing calf feeding strategies is critical for improving performance, health, and weaning transitions of preweaning animals. Despite the updated National Academies of Sciences, Engineering, and Medicine (NASEM, 2021) , decision support tools integrating these equations for simulating optimized calf feeding strategies remain limited. To address this gap, we developed and tested the CalfSim, a free, user-friendly decision support tool designed to simulate and optimize feeding plans for dairy calves. CalfSim incorporates inputs that farmers can readily collect, enabling users to establish baseline scenarios, explore "what-if" questions, and evaluate the impacts of nutritional strategies on calf performance and rearing cost. The tool is built based on NASEM (2021) equations, with adaptations for predicting energy-allowable growth and solid feed intake under varying conditions. CalfSim's performance predictions were assessed using data from 27 studies, 24 from the and 3 other unpublished studies (n = 76 treatments, 258 BW observations, and 1,585 calves), demonstrating accurate and precise predictions (root mean square error = 8.56 kg, R = 0.91, and concordance correlation coefficient = 0.93). However, farm-specific factors (e.g., disease incidence, environmental stress, genetics) can influence predictions, and these factors are not accounted for. This highlights the need for on-farm data to assist users in making more informed decisions (e.g., by comparing scenarios, calculating cost per kilogram of gain). CalfSim provides actionable insights for designing cost-effective feeding plans, making it a valuable resource for dairy nutritionists, farmers, students, and consultants.