The effect of training sessions and feeding regimes on neuromodulator role of serotonin, tryptophan, and β-endorphin of horses

We tested the hypothesis that diet affects equine feeding behavior and that diet composition affects a shift in energy metabolism characterized by a wide range of neuroendocrine changes. We investigated the effects of training sessions on circulating serotonin (5-HT), tryptophan, and β-endorphin (β-EN) concentrations in horses to ascertain whether two different isoenergetic diets would affect this response. Thirty-six Dutch Warmblood horses were randomly distinguished in 18 horses fed with a low-fiber diet (LF) and 18 horses fed with a high-fiber diet (HF). The training session was represented by a medium-heavy exercise and consisted of 21 minutes/day of walk, 36 minutes/day of trot, 15 minutes/day of canter, for a total of 72 minutes/day. At the end of this session, a set exercise test was performed. There was a significant increase in plasma 5-HT (P < 0.0001) and β-EN (P < 0.0001) concentrations following exercise compared to baseline values, in both HF and LF groups. No significant changes were observed for plasma tryptophan concentrations after exercise. A two-way analysis of variance showed significant effects of medium-heavy workload exercise treatments and time points of sampling during exercise on 5-HT and β-EN changes. Plasma 5-HT and β-EN patterns are presumably linked to the workload exercise effect, as shown by their increasing trend in both HF and LF groups.