Plasma amino acids and muscle metabolism in horses

The aim of this study is to contribute to the determination of normal values for blood concentrations of 20 different amino acids in horses under standardized conditions. Furthermore postabsorptive changes and the influence of exercise on the amino acid levels in blood plasma are to be examined together with some parameters related to muscle metabolism. To investigate postabsorptive changes in plasma amino acids blood samples will be taken repeatedly of a homogenous group of horses, first in the morning before feeding and furthermore at two hour intervals after feeding up to eight hours after the meal. To investigate the influence of exercise blood samples will be taken from standardbred trotters immediately before and immediately after standardized training. Blood samples will be analysed for amino acids in the plasma using HPLC technique. Additional parameters (CK, LDH, Lactate, 3- methylhistidine) will be measured to give further information about the muscle metabolism during exercise. In a third part of the study it is planned to investigate the influence of exercise on muscle metabolism. 5 standardbred trotters will be trained to run on a treadmill. Muscle biopsies will be taken before and after the treadmill exercise and will be analysed for the presence of any changes in catabolic enzyme activity, such as catepsin, ubiquitin, Glucose-6-Phosphate: NADP+ oxidoreductase and acid phosphatase. Furthermore the expression of metabolism regulating gene products will be investigated using real time RT-PCR. As little is known of the amino acid metabolism in horses especially during exercise the determination of reference values for amino acids and further investigation of muscle metabolism during exercise are the prerequisite to optimize nutrition and amino acid supplementation for exercising horses and thus to prevent muscle catabolism. Optimal nutrition and prevention of muscle catabolism are requirements for maintenance of good health and animal welfare especially for those horses used in athletic competitions such as races or show jumping. The determination of reference values for amino acids in horses will increase the basic knowledge in exercise physiology. The results of this study will be a basis for further studies about the benefits of general or individual amino acid supplementation and other nutritional support measures for horses; but it will also serve as a model for muscle physiology in human athletes, as race horses can be considered as well trained athletes.

The objective of the present study was to investigate amino acid concentrations in the blood and changes in the muscle metabolism in horses under the influence of feeding and exercise. Amino acids (AA) are the building blocks of protein and thus can be found ubiquitously in the body either in free form or as part of structural and functional proteins. The study was carried out in three parts. In the first part, concentrations of amino acids were measured before and at certain time intervals after feed intake in 10 young horses. Concentrations before feeding showed little influence by day or by individual, whereas concentrations after feeding showed stronger individual differences between horses. All AA increased after feeding, reaching their maximum concentration at 2 hrs. Most concentrations returned to fasting concentrations at 8 hours. The second part of the study focussed on changes of amino acid concentrations after intense exercise. Blood samples were taken from 37 standardbred Trotters (trotting race horses) before and after training. Distinct changes of AA concentrations were noted immediately after exercise, with some concentrations higher and others lower than before exercise. Some AA were not influenced by exercise. Sampling was repeated in 20 horses and a significant effect of sampling day was seen. In the third part of the study 9 trotting horses were exercised on a high speed treadmill and blood and muscle samples were taken to investigate changes in the muscle as well as in the blood. Changes in the blood concentrations were similar to those measured in part 2. Analysis of muscle samples showed a higher activity of one protein degrading system immediately after exercise and four hours after exercise. This might, to some extend, explain the increased concentrations of amino acids in the blood. A good understanding of the events taking place inside the muscle during exercise is important to understand exercise effects on the muscle, to avoid non-physiological training effects and to optimize nutrition and thus help keeping the animal healthy.