Effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behaviour in horses

Noble, G. K., Brockwell, Y. M., Munn, K. J., Harris, P. A., Davidson, H. R. B., Li, X., Zhang, D. and Sillence, M. N. (2008) Effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behaviour in horses. Equine Veterinary Journal, 40 1: 51-56. doi:10.2746/042516407X238503

Author Noble, G. K.
Brockwell, Y. M.
Munn, K. J.
Harris, P. A.
Davidson, H. R. B.
Li, X.
Zhang, D.
Sillence, M. N.
Title Effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behaviour in horses
Journal name Equine Veterinary Journal   Check publisher's open access policy
ISSN 0425-1644
Publication date 2008-01
Year available 2008
Sub-type Article (original research)
DOI 10.2746/042516407X238503
Volume 40
Issue 1
Start page 51
End page 56
Total pages 6
Place of publication Hoboken, N. J.
Publisher John Wiley & Sons
Collection year 2009
Language eng
Subject 0707 Veterinary Sciences
Formatted abstract
Reasons for performing the study: L-tryptophan is a common ingredient in equine calmative products, but its effectiveness has not been demonstrated in horses.

Hypothesis: To determine whether a commercial dose of L-tryptophan increases plasma tryptophan and alters behaviour in horses fed a roughage or concentrate meal.

Methods: L-tryptophan (6.3 g) or placebo (water) was administered per os in a cross-over design, to 12 Thoroughbred horses (503 ± 12.1 kg bwt), just before a meal of lucerne hay or oats. Plasma tryptophan was measured by gas chromatography. Horse behaviour was observed in an empty enclosure, then in the presence of an unfamiliar person and a novel object.

Results: Total plasma tryptophan increased 3-fold in both studies, peaking 1.5-2 h after dosing. After the peak, tryptophan remained high for several hours if the horses had been fed hay, but fell sharply if fed oats, consistent with the glycaemic responses to these meals. However, the ratio of tryptophan to 4 large neutral amino acids (phenylalanine, tyrosine, leucine and isoleucine) increased in the tryptophan-treated horses to a similar extent and for a similar duration, with both diets. The presence of a stranger or novel object increased heart rate (P<0.05), but caused no behavioural effects that were altered by tryptophan, regardless of the diet.

Conclusions: 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.

Potential relevance
: Further work is required to refine behavioural tests and identify an effective dose of L-tryptophan in the horse.
Keyword horse
acute hemolytic-anemia
amino acids
nutrition supplement
Q-Index Code C1
Q-Index Status Provisional Code

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Agriculture and Food Sciences
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Citation counts: TR Web of Science Citation Count  Cited 4 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 6 times in Scopus Article | Citations
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Created: Thu, 03 Sep 2009, 10:35:56 EST by Mr Andrew Martlew on behalf of School of Animal Studies