The Effect of Tryptophan Products on Stressful Horses

Thu, 11/10/2011 - 10:37
Veterinary News

Competition horses are often subjected to stressful situations. Several supplements that claim to reduce equine stress levels are marketed worldwide, yet the effectiveness of these supplements remains ambiguous.

A study by S. Liss and Inga Wolframm aimed to investigate the effect of an orally administered tryptophan product on horses ? reaction to an acute stressor.

Sixteen mature warmblood riding horses (N=16, 3 gelding, 13 mares) were used in the study. Loading onto a two-horse trailer parked in an enclosed arena served as the acute stressor for the purpose of this study. Horses were used as their own controls in a blind cross-over design and were tested on two separate testing days, held two weeks apart.

During the experimental condition each horse was fed one oral dose of tryptophan (2.0 mg kg-1) three days prior to and on the day of the experiment, according to the manufacturer ?s recommendations and in addition to their usual rations.

For the control condition horses were fed only their normal rations. Heart rate was recorded during rest for each horse before and after loading and during the process of loading for all horses (n=16).

Saliva samples (n=10) were collected from ten horses 40-60 minutes prior to the test (sample A) and 10-20 minutes after the test (sample B) on both test days. Behaviour was recorded with an ethogram at rest for each horse (n=16) and throughout the process of loading. Most important results revealed that salivary cortisol concentrations of horses during the experimental condition did not differ from cortisol concentrations during the control condition (t (9)=0.16, P>0.05).

Furthermore, heart rates of horses during the experimental condition did not differ from the heart rates during control conditions (t(15)=-1.66, P>0.05). Behavioural parameters of horses during the experimental condition did not differ significantly from their behaviour during the control condition (vocalization t(15)=1.37, P>0.05; defecation t(15)=-0.9, P>0.05; time spent chewing t(15)=-0.9, P>0.05)).

Findings indicate that a dosage of 2.0 mg kg-1 a tryptophan-based product aimed at reducing stress-related symptoms in the horse does not seem to have the desired effect.

The current study seems to indicate that nutritional supplements aimed at relieving stress symptoms in the horse may not always be effective. In order to prevent horses to adversely react to stressful situations riders, trainers and handlers of horses should spend time building the horse’s trust under different circumstances.

-- 2011 ISES Conference Abstract

Related Links
ISES 2011 Bridging the Gap Between Science and Practice
Wolframm, Clayton, McLean: Where Science Becomes Knowledge