Tryptophan, marketed as a calming supplement in horses for years, was found to have to effect on reactive behavior in horses, researchers found. Claims for tryptophan have included that it can help horses focus and relax, reducing spookiness and tension. Supplements that have tryptophan in them are used on horses for transportation and competition, reports HorseTalk.
Tryptophan is an amino acid that is a precursor to serotonin, which is involved in mood, memory, appetite, sleep and learning in both horses and humans. Serotonin-enhancing drugs in people are used to treat depression, anxiety and obsessive-compulsive disorder.
Brittany Davis and Colorado State University colleagues Jason Ransom, Terry Engle and Temple Grandin used 11 horses (nine geldings and two mares) at the university's Equine Teaching and Research Center for the study. The horses were draft crosses and Quarter Horse types that were between 2.5 years old and 16 years old.
Each horse was assigned one of four treatments: low (20mgTryptophan/kg bodyweight), medium (40mgTrp/kg BW), high (60mgTrp/kg BW) or no supplementation (these horses served as the controls). The horses were treated for three days, then given four days where they didn't receive the treatment.
Researchers assessed the horse's physiological response and behavior using a reactivity and a startle test. The startle test recorded the amount of time it took a horse to move away from a stimulus like an umbrella opening while an alarm sounded.
No significant behavioral changes were found after the horses were treated with tryptophan, the scientists reported in the journal Applied Animal Behaviour Science, but the team did find different physiological effects on Day 1 and Day 3 of the study.
On Day 1, all treatment groups showed at least one change. The low-dose group appeared to have a sedative effect in terms of changes in heart rate and serum lactate levels. The medium- and high- dose groups had reduced cortisol levels. Interestingly, on Day 3, the researchers recorded no change or, for the medium-treatment group, a significant increase in the time for heart rate to return to normal after startling.
It was concluded that “supplementing horses with tryptophan may produce desired results only a few hours after administration; longer-term use may provide no additional benefit or may even have unwanted effects.”
It was recommended that owners look for the causes of unwanted behaviors before turning to calming supplements or drugs. Suggestions included more turnout time or training, or treatment for an underlying disease to make horses quieter.
Read the full study here.
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