Resting concentrations of the plasma free amino acids in horses following chronic submaximal exercise training

Six horses were conditioned on a treadmill at a constant speed of 5.6 km/hr on a 12.5% grade for gradually increasing periods of time over 14 days in order to determine the effect of repeated submaximal exercise on the concentrations of plasma free amino acids, protein metabolism, and plasma volume. Following 14-days of training, plasma volume increased (29%, P<0.05), as did total circulating content of plasma protein, albumin and urea. Urinary urea nitrogen excretion decreased (P<0.05) with exercise training. After the first week of training, the concentration of glycine had decreased (P<0.05) and the concentrations glutamic acid, arginine and alanine were increased (P<0.05) when compared to their corresponding pre-training (control week) levels. Compared to pretraining levels, there were decreases (P<0.05) in aspartic acid, histidine, arginine, valine, phenylalanine, isoleucine, and lysine, following the second week of training. Following a week of recovery, all resting concentrations of plasma free amino acids; when compared to their pretraining control; had decreased, with the exception of three nonessential amino acids (glutamic acid,serine, and glycine). Based upon the results of the present study, it would appear that exercise training produced a significant change in the amino acid and protein metabolism of the horse.