The Ruminant Farm Systems (RuFaS) model is a platform to support future research and actions for sustainable dairy...

The Ruminant Farm Systems (RuFaS) model is an open-source, modular, whole-farm simulation platform designed to support interdisciplinary research, innovation, and decision making in sustainable dairy production. This review outlines RuFaS structure, functionality, current applications, and potential for further development. Through integration of biophysical modules for animal, manure, soil and crop, and feed storage systems, RuFaS enables comprehensive evaluation of management strategies, environmental interventions, and productivity outcomes in a whole-farm context. The RuFaS model facilitates hypothesis testing, multi-objective analysis, scenario evaluation, and identification of research gaps by simulating interactions and trade-offs across biological, environmental, and management domains. The model's current applications include its integration into the Farmers Assuring Responsible Management Environmental Stewardship program for GHG accounting and its use in evaluating innovations in nutrition, breeding, and manure management technologies. Its modular architecture supports rapid prototyping, modeling at different scales, and uncertainty analysis, making it adaptable to diverse research questions and stakeholder needs. Finally, it highlights the critical role its open-source foundation has for promoting transparency, reproducibility, and collaborative development across disciplines. Its transparent development process, hosted on GitHub under a GPLv3 license, invites contributions from across disciplines and institutions. Scientists are encouraged to explore RuFaS as a tool for advancing their own research, contributing to model development, and engaging in a shared effort to improve the sustainability of dairy systems.