[Swizec]

Where does the phrase "Sweating like a horse" come from then?

And I've often heard people complaining that training horses in hot weather is horrible because they get sweaty and all the dust sticks to them.

While I have never myself witnessed a horse sweat, I've read/heard enough references to the sweatines of horses that I assume horses do in fact ... sweat.

[rimantas]

They key is "not efficiently enough". The body volume (where heat is produced) is propoprtional to the cube of linear dimensions, when surface area is proportional only to the square — hence the bigger you are the harder it is to get read of extra heat. And vice versa: the smaller you are the more effort it takes to keep yourself warm.

[alter8]

> (...) get read of extra heat.

rid

[geekagirl]

There's a tool for grooming horses called a "sweat scrapper" for a reason. :)

If you ever watch a horse race or any other time a horse is working hard and fast, you'll see white foam near where the reins touch the horse's neck and and anywhere else there's friction. That's frothed up sweat.

[JPKab]

Horses absolutely do sweat.... however, this is where the bipedal aspect comes into play.

Not only is a bipedal gait more efficient over long distances, but the fact that humans have a mostly hairless torso which is directly perpendicular to the direction they are running means two things: a maximum amount of surface area of sweaty skin is being exposed to moving air vs. body mass it has to cool. Much greater than a quadraped's.