Ok, the question at hand is whether feeding corn to poultry during hot weather is detrimental. The traditional wisdom is that it makes the bird hot which can lead to greater heat stress and even death in hot weather.
When nutritionists talk of corn being a "hot" feedstock they are referring to the caloric content. Corn is much higher in calories per pound than most cereal grains. People then mistakenly assume that a "hot" feed must make an animal hotter. In defending this they say the excess calories must produce more heat making the animal hotter or they think that that "hot" refers to the animal's temperment, that feeding excess calories makes
them more energetic thus burning excess energy that increases the animal's temperature.
Getting down to the basics of nutrition, a complete ration consists of proteins (amino acids), carbohydrates, lipids (fats), vitamins and minerals. Energy available in a ration is stated in calories. If you were to burn a portion of a ration in a flame to extract all energy you would be measuring the Gross Energy available in kilocalories per kilogram.
All of this energy is not availale to the animal. A certain portion of energy is passed on through fecal matter. The remaining is termed Digestible Energy. A portion of this energy is passed on through the urine and creation of gases. What is left is Metabolizable Energy, but once again all of this energy is still not available to the bird. A portion of this energy is expended as heat in digestion and metabolic processes. This portion is referred to as the Heat Increment. What is left is Net Energy used in maintenance and production. Maintenance being the energy used in daily activities and production being energy used in growth, replacement, and reproductive products.
The Heat Increment is what we are concerned with. The heat produced in digestion is related to the fiber content of the feedstock. The higher the fiber, the more heat. Heat produced in metabolism differs among the nutrients in a feed ration. For protein the heat increment is 20-30%, for carbs, 10-15% and for fats, 5-10%. (Best numbers I could come up with, they vary among different texts).
Based on this, some nutritionists recommended formulating feed rations by Heat Increment to reduce heat stress in livestock. Since animals cut back on feed intake during hot weather, they recommend increasing total energy in the ration to help the animal maintain on the reduced intake. They also recommend lowering protein levels and feeding more carbs, or even better, fats, which have the lowest Heat Increment. Additionally they recommend low fiber rations to reduce the heat increment from digestion.
So where does that leave corn? Well corn is high energy, easily digestible, and low in protein, everything that the nutritionists recommend to reduce heat stress.
Conversely, in cold weather, birds will eat to meet their energy requirements. If a coop is maintained at moderate temperatures feed intake stays fairly normal. If the temperature plunges the birds eat more to maintain their temperature. If they are eating an excess of standard rations they are getting too much protein in which the excess is excreted in the urine, leading to poor feed conversion. Once again, corn to the rescue! Supplemental corn can help them meet their energy requirements and cut their protein intake back to required levels.
