It was terribly cold in West Texas last night, horrible rain (rain? It rains here??), but I was thoroughly convinced I would see dead 4-week old chicks this morning in my coop. But they were all fine and healthy. I agree with the conditioning, I think its best to allow them a little feeling of the cold or they wont get used to it. And the quicker and more you do it now, the less worrying you will do later.