You are missing one of the main reasons for heavy lather on a horse. It has to do with a diet high in calcium. Horses that consume a higher % of alfalfa in their diet usually get 2-3 times the calcium they need and this creates a heavier lather.
This is one of the main reason that endurance riders avoid feeding a high % of alfalfa to their endurance horses. A thin watery sweat helps to disapate body heat much more effectively than a heavy lather sweat. Endurance horses that need to sustain an 8 hour performance in which it is critical they disapate heat from the muscles. Most performance horses have a 2 minute cutting run, a 16 second barrel run. So they are not concerned about long term heat management nor about long term muscle twitch.
But endurance riders like to give alfalfa during the race, because the extra calcium helps with the muscle triggers that cause the muscles to twitch. Calcium is stored in the bones of the body, But the retrieval of that calcium is way too slow during a 50 mile endurance race, So feeding calcium rich food just before and during the race helps the horses perform better. But since they have not been eating it all week long, they don't get the heavy lather.
Performance horses, such as the Kentucky Derby horses mentioned above, are often fed a diet high in alfalfa because it contain more calories than a diet of straight grass and the calories are needed for a horse under a heavy work out routine.
Do some searches on nutritional needs of distance horses and you can find plenty of dicusssion about the difference in diets and what they produce.
Last edited by Painted Horse; 05-09-2011 at 01:15 PM.