Walters / Johnson / Micro Sweeper Ice Preventors

Below is another way to do the constant flow heat trick - the Micro Seeper:

Pictured above is the Johnson / Walters Ice Preventor, and
the Baker Products Micro Sweeper Ice Preventor.
Both of these inventions provide constant flow heat and are an automatic way to start water running through your livestock waterers when the temperature get close to the freezing mark. They start flowing fresh water through the trough which is warmer as the temperature drops to around 40 degrees. The Baker Products Company also makes a device called the Ice Sweeper  (click link to see it) that will automatically start draining your waterer when it gets cold enough as well. The float valve will then open letting new warmer water enter the waterer thus accomplishing the same constant flow heat trick. 

By the way: Your waterer design should be providing a way for the extra water to leave the trough via an oveflow pipe or other means so that the overflow water does not make a big muddy mess around the waterer.

Other livestock valve & float options:
       Ritchie Valves & Floats
       AY McDonald
       Watts / Flippen
       Watson Manufacturing
       Jobe / Stay Tuff
       Hudson Valves