Calmatives for the excitable horse: a review of L-tryptophan.

This research article discusses the use of tryptophan-based treatments to calm overly excitable horses. The study suggests that despite the popular use of tryptophan, there is not enough scientific evidence to confirm its effectiveness in horses, and heavy dosage may even cause harmful effects.

Review of L-Tryptophan as a Calmative

The paper begins by discussing how preparations containing tryptophan are widely marketed as calmative agents for horses. Tryptophan, a precursor for the neurotransmitter serotonin, is associated with sedation and the inhibition of aggression, fear, and stress in various animal species and humans.

• Tryptophan supplementation has been demonstrated to decrease aggression in humans, dogs, pigs, poultry, and fish, and to potentially decrease fearfulness and stress in animals such as calves, vixens, and poultry.
• However, tryptophan does not appear to affect behaviors more closely associated with excitement, like hyperactivity in dogs.

Variations in Tryptophan Response

The paper further explores how the behavioral response to tryptophan can vary based on numerous factors in animals.

• These factors include age, breed, and gender, and can be modified by diet, exercise, social status, and level of arousal.
• Importantly, the response to tryptophan is species-dependent. Despite its widespread use, there are no scientific publications that confirm the efficacy of tryptophan as a calmative in excitable horses.

Effects of Tryptophan in Horses

The few studies where tryptophan has been given to horses have shown a range of results.

• Low doses of tryptophan (compared to those in commercial preparations) may cause mild excitement in horses.
• High doses can decrease the horses’ endurance capacity and can cause a severe condition known as acute haemolytic anaemia if administered orally. This is due to the production of a toxic metabolite in the horse’s hindgut.

Call for Further Research

The study advocates for more research to confirm the efficacy of tryptophan in horses and to determine a safe therapeutic dose range.

• The use of tryptophan as a calmative is popular, thus it’s critical to establish if it is indeed effective and safe for horses.
• In the meantime, the data suggest that it would be imprudent to rely on tryptophan to calm an excitable horse. Instead, a greater effort should be made to identify the underlying causes of the horse’s excitability and to explore more suitable non-pharmacological remedies.