How liniment works
There are a number of different brands of equine liniment, each with their own unique formula. Most, however, have the same active ingredient: Menthol.
Menthol concentration in veterinary liniments on the market in both liquid and gel form vary significantly from around 1% to 7%. There is a study that was done comparing menthol concentration to effectiveness, and it found that concentrations as low as .5% and as high as 10% actually produced less cooling sensation on the human test subjects than those with a more moderate concentration. This means you're looking for a menthol concentration ideally around the 4-7% range for maximum effectiveness. (4)
A word of caution on that note; while any brand of liniment can cause this, the enhanced cooling "tingly" sensation caused by the target menthol concentrations, while more effective, may also trigger a more excitable reaction in your horse for a couple minutes when you first apply it. This can happen with any method of application, but most noticeably when applied as a body wash.
Pay attention to the blend of other ingredients found in the various liniments on the market. You'll see many of them with the characteristic green color, which is almost always achieved using artificial coloring. This may or may not be a big deal for you personally and if so look for a liniment that leaves the coloring out, there are several on the market. Other ingredients should include some form of skin moisturizers and healing agents. There should be various rubefacients, which are substances that cause the blood vessels near the skin to open up, or vasodilate, to allow increased circulation to the affected area. Finally, there are usually some emulsifiers, humectants, and other agents which help all the ingredients become and stay blended together.
As with all therapeutic treatment regimens, it is wise to consult with your veterinarian before you begin treatment. Package directions should also be followed, as some manufacturers may or may not recommend various methods of application. This includes all listed uses below.
Liniment and Brace
Use before and after exercise for optimal effect. First wet down the areas to be treated with warm water to open the pores of the skin for faster penetration. Then apply liniment full strength and gently rub in. Vigorously rubbing/massaging is not recommended and may cause scurfing and blistering of the skin. Applying liniment full strength under the saddle and girth area is also not recommended.
Mix one part liniment with five parts warm water and apply to all areas desiring treatment with a sponge. Allow to drip dry instead of scraping off with a sweat scraper.
Two hours before competition or workout, coat the horse's lower legs with liniment. Wrap with cold water bandages. Pour cold water over legs, place legs in bucket full of ice water, or apply ice boots. To extend freezing action, re-apply Trainer's Choice every 30 minutes leading up to competition or workout.
Completely coat area to be wrapped with liniment. Work into coat gently, do not vigorously massage. Cover with sheet cotton and wrap with standing bandage.
*Caution* DO NOT apply plastic wrap or other method of "sweating" as you will blister the skin. Repeated wrapping with liniment over several days may also cause blistering, so use this method with caution.
(1) R. Eccles (1994). "Menthol and Related Cooling Compounds". J. Pharm. Pharmacol. 46 (8): 618–630. doi:10.1111/j.2042-7158.1994.tb03871.x. PMID 7529306.
(2) Galeotti, N., Mannellia, L. D. C., Mazzantib, G., Bartolinia, A., Ghelardini, C.; Di Cesare Mannelli; Mazzanti; Bartolini; Ghelardini (2002). "Menthol: a natural analgesic compound". Neuroscience Letters. 322 (3): 145–148. doi:10.1016/S0304-3940(01)02527-7. PMID 11897159.
(3) G. Haeseler; D. Maue; J. Grosskreutz; J. Bufler; B. Nentwig; S. Piepenbrock; R. Dengler; M. Leuwer. (2002). "Voltage-dependent block of neuronal and skeletal muscle sodium channels by thymol and menthol". European Journal of Anaesthesiology. 19 (8): 571–579. doi:10.1017/S0265021502000923.