When is too cold for pot belly pigs??

Question
We live in the south-western part of Wisconsin and the weather report is calling for below zero temps starting tomorrow. I have 2 male/neutered pot belly pigs that share a pen in a steel shed barn. They do go outside but I will keep them in while we are going through this cold snap and blizzard. They have ample straw to burrow under. They are about 100 lbs a piece. What actually is too cold before I have to put some time of heating lamp in their pen? They share the barn with 3 goats, chickens and sometimes 2 very spoiled mini burro's. Also, I feed them Mazuri pig chow for less active pigs (1 Cup 2 x's a day each) and was wondering if I could supplement rabbit pellets in with the pig chow to cut down on cost. I had our local feed mill compare the ingredients,especially the protein %26 fiber and it is quite similar. Please let me know.  

Answer
Below zero is very cold! Wind makes the cold worse, because body heat is blown away.

The key words in shelter are dry and windproof. Also, the temperature inside the barn is more important than the temperature outside.

I'm not a goat or burro expert, but the goats I had tended to potty where ever. The piggies are much picker, and do not like to potty in their beds. This is a good thing, because straw soaked with pee does not keep them warm. So try to arrange things so the piggies have their own sleeping area that nobody else can pee in.

Heat lamps + straw can = fire. Fresh, dry straw, the best kind for bedding, catches fire pretty easily. So I personally never recommend heat lamps anywhere around straw.

Instead, I suggest insulating the floor by putting down a stall mat. Then, create a mini shelter by stacking bales of straw, two or maybe three high, in an L or U shape, and stuff it with loose straw. The piggies will burrow down into the loose straw, and the stacked bales will provide excellent insulation. You can throw an old blanket over the top of the bales as a "roof". This set up inside a dry, windproof barn will provide more than enough warmth for 2 piggies sleeping together.

The ingredients inside the food bag are more important than the name on the outside. If the rabbit pellets are very similar in both nutritional analysis and ingredients, it's probably ok to mix them with the mini-pig pellets. Complete horse pellets (not sweet feed) is also usually pretty close to pot-bellied pig food.

Water is important even in winter. The piggies will appreciate getting slightly warm (70 - 80 degrees) water when the weather is very cold. An easy way to do this is just fill your water container the night before, and leave it overnight in a warm place in your house.