The role of Tryptophan in your horse’s diet

L-Tryptophan is an amino acid, which, if lacking in the diet, can cause anxiety. Serotonin is made from L-Tryptophan and serotonin is the neurotransmitter in the horse’s brain that helps your horse feel calm. You can see why a horse lacking in L-Tryptophan might be spooky and tense.

Doubts raised on how beneficial Tryptophan is

A friend sent me this (most excellent) review of L-Tryptophan as a calmer for horses: http://bit.ly/1A8hRaS.

Why we think supplementing Tryptophan for horses makes sense

This is my response to her email:

“Thank you for sending this – it’s an excellent article and the authors must’ve spent weeks gathering all this info together.

For me, this article was very slightly biased against Tryptophan. Which is probably why it appeared where it did. But they do still put all the relevant facts forward, which is commendable.)

The points:

1. “There are zero studies that confirm Tryptophan (Trp) as a calmer in horses.” This is true. It is also true of a huge number of other nutraceuticals. Research into naturally occurring, easily available ingredients is limited, because of the lack of financial return to big pharmaceuticals. Especially in horses. It doesn’t mean that Trp isn’t a valid calmer.
2. “Of the work that has been done, very low doses (25 and 50mg per day) cause mild excitement. (Bagshaw study.)” As mentioned here, this study was very flawed. Only a few horses, only a few hours, too low a dose, breed differences. IMHO the poor horse probably just got a bit bored of standing around having their heart rate measured. I think this dose of Trp did absolutely nothing.
3. “Very high oral doses (350 and 600mg/kg bodyweight) lead to anaemia, increased respiration and haemolysis.” This also doesn’t mean that Trp doesn’t work as a calmer. It just means that very high doses are dangerous. Very high doses of carrots are also dangerous. That doesn’t mean that it is bad to feed horses carrots.
4. The daily dose of Trp included in our UK version of Calm Mix is 2000 mg per day. This is above the dose that Bagshaw found to cause slight excitement (25 or 50mg per day) and way below the dose that Paradis found to cause anaemia (175 000 mg or 300 000 mg per day).
5. They then make the point that other factors (diet, exercise, gender etc.) influence the uptake of Trp and therefore the effectiveness.  This is also true (in fact I think it’s a bit of a no-brainer), but also doesn’t mean that Trp doesn’t work.
6. The one point they make which is that Trp might decrease endurance is valid.  But I guess if you have a horse that leaps around like a maniac for half of the endurance ride, that might also decrease his ability to stay the distance. It’s a judgement call.
7. Then there is the also very valid point that excitability in horses is not exactly well defined. Is it hysteria? Or aggression? Or hyperactivity? Or fearfulness? Because Trp seems (in studies in other species) to have varying effectiveness in controlling these varied symptoms. Aggression, fearfulness and hysteria are decreased by Trp. Whereas hyperactivity isn’t.
8. The one symptom which has strongly been shown to improve with Trp supplementation in other species is depression. Which these authors immediately disregarded because they felt it was irrelevant to horses. I disagree. I think horses can and do get depressed. And that anything that improves mood is bound (IMHO) to improve behaviour.

Also, in our version of Calm Mix for the UK we have added Vitamin D. In a very recent study, Vit D has been found to increase the production of the enzyme Tryptophan Hydroxylase 2 (TPH2). This is the enzyme which drives the conversion of Trp to 5-HTP, which in turn is converted to Serotonin. The conversion of Trp to 5-HTP is the rate limiting step (slows the whole process down). So anything that can increase this step is invaluable in getting a higher Serotonin level in the brain.

Whenever I look at other studies like this, I am more than a bit sceptical. Because, every single day, we get feedback from our customers that Calm Mix works.