Some people put a tennis ball in... At the very least you then have a hole in the ice which will help to break the ice. Never tried it myself though so can't say how good it is!
Thats weird as I was only thinking last night i might put a post about this myself! The only thing I thought of was an apple floating in the water, but had visions of my horse applebobbing in the night and water pouring over my stable floor to make a nice ice rink for him to skate on in the morning.
Put something in that will float - as it moves around stops the water from freezing - failing that some people use salt - not sure if that works though - just another idea!
Tennis ball for stable water and a slightly deflated football for the feild trough... works a treat because it moves around whenever they drink, therefore preventing the top layer from freezing...
A floating tennis ball is supposed to help for some reason. I keep meaning to try this, but it always slips my mind until too late.
My gang had managed to make a hole in their trough yesterday morning somehow. It was a smooth edged hole though, so I really don't know if they somehow melted an area with their warm breath (daft as it may seem)??? However, I still had to use a hammer to break the rest of the ice on the trough as it was a good 2 inches thick.
Am taking 25 gallons of extra water up this evening, as I suspect the underground pipes are now frozen as well, meaning the trough won't fill up automatically until we have a thaw.
We have a football floating in the big troughs in the fields, which has been such a help! Still have to break and remove inches of ice, but it makes it so much easier. Haven't had anything in the stables freeze yet (knock on wood).
Sadly I don't - we have stand pipes and hoses and fill plastic containers. It was -3C at 10.00am this morning (I am in northern Loire). We have lagged our stand pipes with bubble wrap and can get the taps going quite quickly with a bit of warm water.
You could try covering them with gardners fleece - I have coriander growing outside under a fleece. Try putting some sacks of horse manure around the tank.