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Tell Me About Tyrosine


Tyrosine is an amino acid that is beginning find a role in horse calming supplements. Unfortunately a number of the other amino acids used in calmers also begin with “T” creating a huge potential for confusion – especially as some of them work in particularly different ways.

Tyrosine is incorporated into many proteins and itself can be made in the body from phenylalanine. Animals can’t make phenylalanine so if they are not eating enough of that they can run out of tyrosine impacting on the ability to make proteins.

Tyrosine is also used to make a number of hormones and neurotransmitters. These include dopamine, epinephrine (also known as adrenaline) and norepinephrine. It is the broader biologically active chemicals – or the lack of them - that impact most on horse behaviour. When stressed horses produce more of these hormones and that can deplete tyrosine (and tryptophan) levels. A shortage of those two amino acids seems to lead to insufficient levels in the brain and that is what causes the behavioural issues.

Supplementing with tyrosine does not seem to force the production of any of these hormones - so it has no effect if the levels have not been depleted (see below). So it meets our (EquiFeast’s) requirement of being an “enabler” not a drug. At EquiFeast we are passionate that our job is to help horse’s brains to function properly not to force them to be sedated. Having said that the combination of very low levels of tyrosine with high magnesium diets doesn’t seem to be ideal. So we do have a minimum application rate for tyrosine.

This showed up in the trials we ran on tyrosine early in 2019. The outcomes of those trials were roughly:

  • 10% negative effect (with high Mg diets)
  • 30% no effect
  • 60% helped horses with improved behaviour

So, just as with any other calmer, it isn’t always the whole answer.

Field trials are all well and good but we continue to collect data from customers as we now use tyrosine (product designated FineTUNE 1) as part of our fine tuning process. The feedback we get from that process will enable us to refine how and when we use tyrosine in the future.

The really good news about tyrosine is that we seem to be able to use much smaller amounts than we have of Tryptophan in the past. The reason for that is not clear as they are both precursors of serotonin. It is also much more palatable than tryptophan. So tryptophan has been demoted in our fine tuning process and may become less important over time.

The other two amino acids beginning with “T” that are commonly used in calmers are Theanine and Taurine. We do not use either as both interfere with normal brain function by locking on to the same receptors in the brain as diazepam. This makes them non-compliant with FEI regulations as well as being a method of calming horses that we are not comfortable with.

EquiFeast products that contain Tyrosine. This is a long list so feel free to contact us to chat about your horse by phone on 01453 836974 or email

Any of our CORE range of balancers except for EssentialCORE

Any of our Cool, Calm and Collected range of supplements

Sensible Essential and Mare Essentials

Any of our WINNINGEDGE Supplements

FineTUNE 1


Related articles: 

Tell me about Tryptophan

FEI Legal Calmers

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