Wheat middlings and red dog are co-products from the wheat processing industry and are the high-fiber leftovers from production of wheat flour. There is an estimated total annual production of 6 to million tons of wheat coproducts produced in the U.S. and much of that amount is used in the feeding of swine. There has, however, been very little research conducted to determine the nutritional value of wheat coproducts fed to pigs. The present research determined, in 2 experiments, the ileal digestibility of amino acids in 10 sources of wheat middlings that were collected throughout the U.S. and in one source of red dog. The concentrations of DE and ME were also determined and equations to predict the concentration of DE and ME in wheat middlings were developed as well. 
Results indicated that red dog has greater digestibility of amino acids and also contains more DE and ME than wheat middlings. All sources of wheat middlings had relatively low digestibility of lysine indicating that high amounts of  heat most likely is applied to these ingredients during the production process. The digestibility of all fiber components is also greater in red dog than in wheat middlings. The reason for the greater concentration of DE and ME in red dog is most likely that this ingredient contains twice as much starch  and much less fiber than wheat middlings. These differences in composition are likely also the reason for the greater digestibility of AA in red dog than in wheat middlings. As a consequence, red dog has a greater nutritional value in diets for pigs.  Data from this research provide, for the first time, a robust estimate of digestibility values for AA and energy in wheat middlings and for one source of red dog. These values may be used in formulation of diets for pigs.
Overall conclusions:
• Wheat middlings selected from across the U.S. has a relatively constant nutrient composition
• Wheat middlings has a relatively high concentration of fiber and a low concentration of starch.
• The digestibility of amino acids and the concentration of metabolizable energy in wheat middlings is less than previously thought
• Red dog has a greater digestibility of amino acids and contains more metabolizable energy than wheat middlings due to a greater concentration of starch and a reduced concentration of fiber compared with wheat middlings