Nutritional and Genetical Factors Influencing Nitrogen Metabolism and Excretion in Dairy Cows: A Review.

This paper aimed to review the literature concerning nitrogen metabolism and excretion in dairy cows in the light of actual global climate change picture. Nutritional factors like dietary crude protein or dietary carbohydrate concentration have a significant effect on nitrogen balance, through the decreasing capacity of the total N excretion and improving the milk nitrogen efficiency. At the same time, the protein and carbohydrate degradability rates as well as dietary minerals will impact the excretion routes, urinary and faecal. Shifting between urinary to faecal pathway could benefit to the mitigation of air pollution as the faecal nitrogen content is less prone to volatilisation compared to the urine nitrogen. Feed additives such as direct feed microbial, plant secondary metabolites and rumenprotected amino acids can mitigate and shift the N excretion from the urinary to the faecal pathway. Finally, breeding animals for lower MUN traits could also be considered as an efficient approach for a longer-term strategy to reduce N emissions. [ABSTRACT FROM AUTHOR]