Magnesium and B vitamins ease nervousness as they protect the nervous system. Herbs can produce a relaxed state of mind.
Magnesium - it is not uncommon for horses to have a magnesium deficiency as magnesium from hay is not easily absorbed. Horses that are tense, easily stressed or spooked, or have a short attention span may be lacking sufficient magnesium. Try adding 5000 mg of magnesium/500 pounds of body weight.
B Vitamins (B1, B6, B12) - B1 (thiamine) can lessen anxiety and spookiness. B6 (pyridoxine) aids in serotonin production. Serotonin regulates anxiety and creates a sense of calmness. B12 (cobalamin) protects the nervous system, it can only be produced by microbes in the hindgut.
L-tryptohan - an essential amino acid can also encourage serotonin production. Should not be fed with concentrates for best results.
Chamomille - Herb that can ease mild anxiety.
Valerian -Herb that can produce a sedative effect, will test positive on a blood test so should not be used in competing.