What options do horse owners have to calm their mounts? In a recent study*, Australian researchers attempted to show that tryptophan is a safe and effective calming agent in horses. Tryptophan thwarted the researchers, however, showing no calming effect.

“Tryptophan has long been the amino acid accused of causing sleepiness after a turkey supper or helping you fall asleep following a mug of warm milk,” explains Kathleen Crandell, a Kentucky Equine Research nutritionist. She added, “Behavioral reactivity in horses is a safety risk for horses, their handlers and bystanders, which makes safe and effective calming agents important to many owners.”

To determine whether tryptophan could indeed help calm horses, 60 horses were administered a single dose of tryptophan paste delivering up to 120 mg/kg of body weight. Ninety minutes later, the horses underwent a standard “reaction speed test.” No effect on reactivity was observed.

Despite these results, the researchers suggested that further study is warranted to determine whether multiple doses of tryptophan have a cumulative effect on calming. In the meantime, horse handlers are advised to not rely on a single dose of oral tryptophan as a calmative in stressful situations.


*Noble, G.K., X. Li, D. Zhang, et al. 2016. Randomised clinical trial on the effect of a single oral administration of L-tryptophan, at three dose rates, on reaction speed, plasma concentration and haemolysis in horses. The Veterinary Journal. 213:84-86.

Article courtesy of Kentucky Equine Research. Visit equinews.com/newsletters to subscribe to The Weekly Feed, KER's award-winning equine nutrition newsletter.