Considering all the important tasks L-methionine performs it’s perplexing you don’t hear or read more about it.
L-methionine is one of the essential amino acids, meaning the horse must get his supply from the diet because the body cannot manufacture it. Methionine is a structural amino acid which means you can find it in all proteins in the body, from skeletal muscle to hemoglobin, antibodies and enzymes. Methionine is also required for the initiation of building proteins in the body.
Insufficient methionine can play a role in crumbling and cracking hooves.
Methionine can be converted to the other two sulfur containing amino acids, cysteine and cystine. Sulfur bonds between cystine amino acids strengthen the structure of hooves, hair, tendons and ligaments.
Methionine is required for the production of:
- Taurine – central to health of the heart, nervous system and eyes
- L-carnitine – a carrier that is necessary to burn fats for energy
- Metallothionein – a protein which binds excess dietary minerals, and toxics, and carries them back into the bowel for excretion
- creatine – the carrier of high energy bonds for muscle contraction
- glutathione – the body’s master antioxidant
Methionine also functions as a methyl group donor by being the precursor for SAM. Transfer of methyl groups (transmethylation) is involved in a host of body functions including:
- Detoxification reactions in the liver
- Production of epinephrine
- Regulation of the activity of DNA
- Production of the active form of the vitamin folic acid
- Recycling of methionine
- Regulation of the immune response
- Recycling of glutathione into an active form
More is never better even with a nutrient this important but unfortunately we really don’t even know what the equine methionine requirement is! A look at the most common things fed to horses quickly shows they are mostly on the low end for methionine:
Hays also vary in methionine content quite a bit, based on both their protein content and the type of hay. Levels are dropping in many areas since pollution controls have greatly reduced the levels of sulfuric acid in the air, which was serving as a natural sulfur fertilizer.
The current best guess for methionine requirement in adults is that it is 1/2 to 1/3 of the lysine requirement. If your horse has outward signs consistent with inadequate methionine such as weak hoof structure consider supplementing with 2500 to 5000 mg of methionine/day. This is commonly paired with 7 to 10 grams of lysine, another amino acid that is often deficient.
Eleanor Kellon, VMD