The dairy sector is an important component of EU agriculture. However, intense growth has caused an imbalance in the N cycle, with negative environmental impact on groundwater, surface water and the atmosphere. EU-funded scientists working on the project 'Innovative and practical management approaches to reduce nitrogen excretion by ruminants' (REDNEX) aimed to increase the efficiency of dietary protein use by dairy cows in order to decrease N excretion. Previous studies showed that a reduction in protein intake is the best way to reduce N excretion in cows, sheep and goats. However, the challenge is in maintaining decreased excretion without falling below the required dietary protein levels for healthy animals and satisfactory production of high-quality milk. To address these issues, the project developed two detailed mathematical models of N use for protein synthesis and N excretion. These models monitor multiple variables throughout the year and assess how changes such as modified nutrition affect N use and excretion at the herd level. REDNEX showed that decreased dietary protein did not influence the amount of N available to produce proteins. Further, adding essential oils to grasses or antibodies against ammonia-producing bacteria in the rumen does not affect the efficiency of protein use. However, preliminary studies showed that improving dietary starch content and the amino acid profile of dietary protein improved cows' metabolic efficiency. Another area of project work involved developing several rapid analyses and biomarkers to improve the speed and accuracy of these models. REDNEX outcomes should assist dairy farmers in decreasing N waste while maintaining the health and productivity of their herds. The management tools will have important impact on farm profitability and on the ecosystem in which a farm is located.
Nitrogen efficiency, nitrogen excretion, ruminants, dietary protein, metabolic efficiency