Drop the temp in the brooder at least 5 - 7 degrees per week of age for the chicks. Are they spread out from each other near the edges (walls) of the brooder? If so that means they are too hot. The only time I ever saw chicks pant that was not heat related is when I was a teenager and raised chickens with my aunt and uncle. A few developed a respiratory illness that closed their nasal passages so the little guys and girls had to pant to breath. We treated them with a mild anti-biotic and in a couple of days the were fine. It was easy to diagnose because they had a small discharge out their noses and it was easy to see their little passages blocked.