Objective 1: Develop or adapt poly-phenol systems in forage legumes for improved N use efficiency in dairy production systems. Subobjective 1.1: Evaluate efficacy of the polyphenol oxidase (PPO)/o-diphenol system on preserving true protein during ensiling and improving N-use efficiency. Subobjective 1.2: Determine the chemical basis for proteolytic inhibition caused by PPO-generated o-quinones. Subobjective 1.3: Develop strategies to produce optimal levels of PPO substrates in alfalfa. Objective 2: Develop or adapt tannin systems in forage legumes for improved N use efficiency in dairy production systems. Subobjective 2.1: Determine the chemical basis for protection of protein during rumen digestion and providing elevated levels of escape protein into the hindgut by condensed tannins (CTs). Subobjective 2.2: Analyze the effects of harvesting and storage methods on active CT content and protein preservation. Objective 3: Improve forage digestibility and nutrient utilization efficiency in the cow through physiological modifications. Subobjective 3.1: Prevent excessive leaf loss during plant development and harvesting by identifying genetic factors involved in leaf abscission in alfalfa providing a foundation for gene-based strategies for improvement. Subobjective 3.2: Use genetic manipulation of sugar nucleotide biosynthetic pathways to identify avenues for altering cell wall structural polysaccharides and matrix interactions. Objective 4: Improve forage silage quality and preservation to lessen forage losses, improve nutrition value for the cow, enhance soil ecology, and reduce environmental impacts for integrated dairy systems. Subobjective 4.1: Incorporate non-traditional silage additives (novel forages, inoculants, concentrates) and management strategies to reduce forage loss and improve relative nutrition in the animal. Subobjective 4.2: Leverage computational and sequencing technologies to elucidate connections between plant, silo, and animal microbiomes. Objective 5: Develop system-based models to assess the productivity, efficiency, and environmental impact of dairy forage production. Develop a whole-farm dairy simulation model that can be used to assess the impact of forage crop modifications and management on farm-scale nutrient cycling, farm crop and milk productivity, and environmental impacts.