How to prevent an exterior automatic watering system from freezing
The first order of business is to find out where the frost line is in your area. The second is to dig a trench 6 to 12 inches deeper than the frost line from the immediate vicinity of an outdoor frostproof faucet (a frostproof hose bibb at the house sill is ideal) to the pasture. The house end of the trench should be pretty well squared off.

You can get ABS pipe in long rolls, and it splices very easily with nylon couplings and stainless hose clamps. Lay it in the trench. At the house end, it should have a 90-degree nylon elbow pointing straight up immediately adjacent to the faucet or hose bibb. On that end, install a female faucet adapter so it can be screwed directly onto the faucet/bibb.

You can now bury the pipe from the house all the way out to the pasture, except for the last several feet. At the end, where you'll draw water for the trough, install another 90-degree elbow and a "Yard Hydrant" (your local ag supply place will know exactly what I'm talking about). Finish burying the pipe.

At the beginning of frosty weather, you'll now build a small lean-to igloo of hay bales around the new faucet adapter. Don't try to insulate between the house and the "hayloo", let heat coming from the house wall heat it. A typical hay bale's R-value is about R-50, which should be plenty to keep the hose connection from freezing over the winter, considering you're all the way down in balmy NJ. If there's ever any question - say an extemely deep freeze - you can add a little heat with an extension cord and a CFL light bulb (an incandescent may be hot enough to set the hay afire).

Over the first winter, put an outdoor thermometer inside the "hayloo" and another outside it. Every time you remember to, go check both temperatures and record what you find. Then you'll have a very good idea how a hayloo performs, so you can predict about how cold it'd have to be before you add electric heat.