Changes of serum free amino acids in eventing horses at rest and during exercise in response to dietary protein

Although there are published expertise about serum free amino acids, to the knowledge of the authors no data were reported on eventing horses. In this way, it is important to study the concentration of dietary protein and serum free amino acid during exercise in order to improve nutritional strategies. The aim of this study was to investigate the concentration of the serum free lysine (Lys), threonine (Thr), leucine (Leu), isoleucine (Ile) and valine (Val) of eventing horses fed diets with different levels of protein at before and during exercise. Twenty-four Brazilian Sport Horses trained for eventing were used in a randomized block design with 4 diets (7.5%, 9.0%, 11.0% and 13.0% of CP) and 6 repetitions (horses). Horses were blocked according to their experience in competitions. The test protocol consisted of a warm up of walking and trotting and then a gallop starting at 6.0 m/s with increases in speed of 1 m/s every minute up to 10 m/s. Venous blood samples were collected before the test and during exercise. Concentration of Lys, Thr, Leu, Ile and Val from diets and serum free amino acids were determined by HPLC analysis. Total intake values of Lys, Thr, Leu, Ile and Val were affected by dietary protein levels. Differences on the serum free concentrations of Lys, Leu, Ile and Val as a function of the sampling time were observed. The Lys requirement for athletic horses appear to be lower than what is currently proposed. Moreover, the effect of exercise on serum free Lys, Leu, Ile and Val concentration, may be interpreted as an indicator of these amino acids metabolic response.