Meeting the growing demand for livestock protein within limited cropland resources requires adopting intensive farming practices, especially for grain-dependent monogastric animals (pigs and chickens). This study employed a global model to comprehensively estimate changes in nitrogen pollution and greenhouse gas emissions across the whole production chain (including feed production and livestock raising stages) before and after the intensification of monogastric systems. The results show that intensifying monogastric farming can reduce nitrogen pollution and greenhouse gas emission, lower fertilizer use, and free up cropland. When integrated with comprehensively optimized farm management practices, these strategies can yield even greater environmental and economic benefits. The research clearly demonstrates that the intensification of monogastric livestock offers a promising way to food security, environmental protection, and climate change mitigation.