Abstract
Rising feed costs and increasing environmental concerns necessitate the evaluation of sustainable alternatives to conventional protein sources in dairy nutrition. This study investigated the effects of replacing soybean meal with alternative protein sources, including agro-industrial by-products, former foodstuffs, and distillers grains, on dairy cow performance, nitrogen utilization, economic returns, and environmental indicators. Using a controlled mixed-method experimental design, lactating dairy cows were assigned to isoenergetic and isonitrogenous diets differing only in protein source. Results demonstrated that alternative protein diets sustained or improved milk yield and feed efficiency while enhancing nitrogen use efficiency and shifting nitrogen excretion away from environmentally sensitive pathways. Favorable rumen fermentation responses indicated efficient microbial activity and potential mitigation of methane-equivalent emissions. Economically, alternative protein inclusion consistently increased income over feed cost, reflecting reduced ration costs without adverse effects on productivity. Integrated sustainability indices further confirmed the superiority of alternative protein strategies in balancing production, profitability, and environmental performance. These findings indicate that alternative protein sources can successfully replace conventional feeds in dairy rations, contributing to resilient, cost-effective, and environmentally sustainable dairy production systems aligned with global sustainability objectives.