Yep...you should be able to do 40 meat chicks under that, especially if it's next month in PA and you have a nice, snug brooder setup. They won't stay under that heating pad any time at all, as they have a faster metabolism and run a little warmer than do DP chicks. I'd advise to leave both ends of the brooder frame open to air...meat chicks tend to pile up on one another at night if given the opportunity.