Selected aspects of nitrogen metabolism in exercising horses

Goal in deriving requirements is to combine objective criteria about quantity of a nutrient that defines dependent functions. In the case of nitrogen and exercise it becomes evident that muscle activity is not a function depending on a defined quantity of nitrogen; consequently the factorial approach in formulation of requirements answers, exercise needs no protein. But simply the fact that the involved tissue is rich in complex nitrogenous structures like mitochondria, stimulate the question how intensively muscle cell nitrogen is in touch with the kinetic energy performing process of the cell. There are clear changes in the plasma as well muscle amino acid profile; alanine and branched amino acids are of major interest. In a nonspecific response on this kind of amino acid abrasion protein supply should be above maintenance level. The actual recommendations of the NRC include an adjusting factor for protein intake in exercising horses. There is growing knowledge about the degree in amino acid utilization during exercise and the response of the muscle performance on specific amino acids. On the other hand, an overconsumption of protein is inappropriate as it can result in heat and metabolic load of the horse. In conclusion the role of single amino acids for regulation of muscle energy metabolism and restoration, for the mechanisms of fatigue and recovery are challenging further research.vo