Feeding intact protein from soybean meal instead of corn and synthetic amino acids does not affect growth performance, carcass composition, blood cytokines, or mRNA abundance of intestinal amino acid transporters in growing pigs, but net energy tends to be greater in diets with soybean meal

Lay Summary The hypothesis that reducing dietary crude protein in corn-soybean meal-based diets will not increase net energy in diets and will not affect growth performance, carcass composition, nutrient deposition, intestinal morphology, or immune status of pigs was tested. Four diets were formulated with decreasing soybean meal inclusion and increasing corn and synthetic amino acids, resulting in protein levels of 20.0, 16.4, 15.4, and 13.4%, respectively. Pigs (initial weight: 32.2 ± 4.2 kg) were fed these diets for 28 days with samples collected to assess body composition, intestinal morphology, blood markers, and mRNA abundance of amino acid transporters. Results indicated that reducing dietary protein levels did not impact any of the analyzed pig characteristics, but net energy tended to decrease as soybean meal in the diet was reduced. In conclusion, growth performance can be maintained on low-protein diets with synthetic amino acid supplementation, but reducing dietary protein levels may decrease net energy values in diets.