This may be at least a partial answer to my question. Apparently, contrary to the popular belief that corn and scratch generate heat, protein is a bigger source of heat in the diet. Therefore, in an extreme heat situation, like 110 degrees, it would make sense that severely lowering the protein levels would decrease the amount of panting. I've started mixing the flock raiser with scratch and they are definitely better than receiving straight flock raiser. They are also getting a higher level of kitchen scraps, which again, lowers protein and probably increases carbs, fats and electrolytes. Remember, when reading this, that the most efficient source of "energy" is fat, the second most efficient source is carbohydrates:
" The energy content of the diet, along with other nutrients, should be increased. Increasing fat calories should be considered. Dietary vitamin and mineral concentrations should be re-evaluated. The use of vitamin C, as an anti-stress agent, is often considered during periods of heat stress. Choosing the correct coccidiostat is very important as well as the use of antioxidants and mold inhibitors in stored feed. Protein contributes more to metabolic heat production than do carbohydrate and fat. Therefore, feeding imbalanced diets with regards to amino acids will result in increased metabolic heat production. Amino acid balance in the diet is especially important. Efforts should be made to formulate diets with slightly lower protein levels and to utilize synthetic amino acids, especially methionine and lysine."
So, it looks like, when raising broilers in a hotter environment, it may be a good idea to lower the protein total concentration and improve the quality of protein source, perhaps supplementing with methionine and lysine, since these are often limiting amino acids. This week, along with limiting total protein, I have added a bit of meat protein to my mixed flock's treats. They certainly love that idea!
I'm going to do some figuring and pull out my old "Feeds and Feeding" book from graduate school. I may see if I can formulate a ration and have a couple of rations, one for broilers, one for my young, mixed flock, milled by the milling company in Casa Grande, taking some of this information into account.