Well looking at this logically - I personally have not done much research into it.
But what ABOUT beer makes horses sweat? Is it the alcohol? The yeast? The hops?
I don’t think it would be the barely or the water, as both of those are quite common to a horse’s diet.
My knee jerk reaction is that it must be the alcohol. I know I am more prone to a flush and sweating after I have drank - and it doesn’t matter if its beer, wine, or hard liqueur.
http://www.md-health.com/Alcohol-Sweating.html
Alcohol is a chemical substance that can cause vasodilation, or the widening of blood vessels. When blood vessels near the skin dilate or enlarge the skin becomes warm and this triggers the sweat glands to produce the fluid which is called sweat. This process, which is also known as perspiration, is a physiologic or normal reaction which is normally associated with other events such as physical exercise that also causes blood vessels to dilate.
Now - with this theory, light beers would be worthless, as they are very low in alcohol. BUT - Guinness - which so many swear by, is also pretty low at 5%
There is also this theory:
First off, the only beer that actually contains the right stuff to provide the widely accepted treatment for anhidrosis is a pint of Guinness stout beer added to the feed twice daily. Guinness Stout contains higher amounts of vitamins C and some of the B complex vitamins, which is thought to be relevant to its effectiveness. It is the specific ingredients used in processing Guinness Stout, and not the vasodilating effects of alcohol, that produce the beneficial effect. This is evidenced by the fact that Guinness Stout is actually lower in percentage of alcohol than many other lighter beers containing more alcohol but that don’t work.
But - I am not sure what is so magical about Guinness. There are lots of stouts on the market - maybe a cheaper one would work just as well? Maybe one with a higher ABV would work better?