First, I know you don't want to hear this with your love of hatching and chicks, but heat lamps, heat mats etc really suck down the electricity
Second, unless you are using MASSIVELY more heat lamps etc this year than last (and I can't concieve of how much heat lamp use could make your bill rise 5-8x what it was!), it sounds like you have electricity going somewhere you don't know about. As someone suggested, a ground fault is possible -- also, it, errrm, has been known to happen that neighbors, especially ones growing uh illegal plant life under grow-lights, can secretly tap into another house's electric service and cause HUGE electric bills. You need to have someone from the power company come out and check your service.
One thing you can do yourself is to go out to the meter. See how fast it's spinning. Write it down (numbers per time unit)
Now go back in the house and unplug everything, I mean EVERY THING, even the heat lamps and freezer and fridge and all (they'll only be off for a very short while). When you've got everything you can possibly unplug, unplugged, go out and look at the meter again. What is it doing now?
If it is still spinning, go inside and throw the breaker (or pull the fuse) to your water heater if it's electric and anything else you couldn't unplug. Look at the meter again. Still moving? Go in and try to locate the master switch (breaker) for your whole box. Turn it off. Now what is the meter doing? (Now go back in, turn the breakers back on, and plug everything back in <g>) This will give you an idea of where your electricity is going -- known electric devices versus Mysterious Places.
Good luck,
Pat