Scientific and Equine Consultant

Why You Should Avoid Tryptophan Calmers For Horses!


I have had a number of emails and messages recently asking about tryptophan based calmers. The answer is pretty simple – unless you want to excite your horses, avoid them like the plague.

WHY? Studies show that tryptophan in low doses as used in most equine calmers causes EXCITEMENT as opposed to having a calming effect. Higher doses have no effect. This position was recently strengthened by the publication of a further paper on tryptophan in horses (Noble et al., 2016). Studies in people also suggest tryptophan may play a role in IBS.

So, on the basis that the information is in the public domain, I find it surprising that the following list tryptophan in their calmers:

-Calming Serenity
-So Kalm
-Topspec calmer
-B Kalm
-Good as Gold
-Cool, Calm and Collected Bombproofing

Again, why? Suggests that none of these companies have done their homework before “throwing together” a calmer 🙁

AND NOW FOR THE SCIENCE BIT……(apologies to L-Oreal)

Noble GK, Li X, Zhang D, Sillence MN. 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. Vet J. 2016 Jul;213:84-6.

Plasma TRP concentrations were increased (P <0.001) by the administration of TRP paste. However, TRP had no effect on the reaction speed of horses when startled. There was no evidence of alterations in clinical pathology parameters in 432 blood samples. While the safety of these doses of TRP can be confirmed, there was no evidence to suggest that a single dose of TRP is an effective calmative for horses.

The Tryptophan Hydroxylase Inhibitor LX1031 Shows Clinical Benefit in Patients With Nonconstipating Irritable Bowel Syndrome. Brown. P.M. et al. Gastroenterology
Volume 141, Issue 2, August 2011, Pages 507-516. http://www.sciencedirect.com/…/article/pii/S0016508511006226

-In a phase 2 study, LX1031 was well tolerated, relieving symptoms and increasing stool consistency in patients with nonconstipating IBS.

Noble GK, Brockwell YM, Munn KJ, Harris PA, Davidson HP, Li X, Zhang D, Sillence MN. Effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behaviour in horses. Equine Vet J. 2008 Jan;40(1):51-6. https://www.ncbi.nlm.nih.gov/pubmed/18083660

-Plasma tryptophan increases when tryptophan is administered at a dose used in some commercial products, but this is not reflected by marked behavioural changes in the horse.

Grimmett A and Sillence MN. Calmatives for the excitable horse: a review of L-tryptophan. Vet J. 2005 Jul;170(1):24-32.

-In the meantime, available data suggest that it would be imprudent to rely on tryptophan to calm the excitable horse…

Behavioral and physiological effect of orally administered tryptophan on horses subjected to acute isolation stress. C.S. Bagshaw. S.L. Ralston. and H.Fisher. Applied Animal Behaviour Science. Volume 40, Issue 1, April 1994, Pages 1-12.

-Tryptophan at 0.05 and 0.1 mg kg−1 increased both heart rate and activity relative to zero dose under both isolation and visual contact environments, suggesting that oral tryptophan may stimulate horses 2–4 h after dosing rather than having a sedative effect.

Date: July 13, 2017