Short-Term Partial Replacement of Corn and Soybean Meal with High-Fiber or High-Protein Feedstuffs during Metabolizable Energy Assay Influenced Intestinal Histomorphology, Cecal Short-Chain Fatty Acids, and Selected Nutrient Transporters in 21-Day-Old Broiler Chickens

SIMPLE SUMMARY: During metabolizable energy evaluation for feedstuffs, the feedstuffs being tested are usually incorporated into a standard diet. High levels of substitution of the test feedstuff into the standard diet inevitably result in changes to the chemical profile of the newly composited diet. Such changes may result in very high levels of fiber, protein, or other components, but the effects of such changes on growth performance, gut health, or nutrient transport in the intestine are usually not investigated. In the current study, the inclusion of low-protein soybean meal, wheat bran, soy hull, corn gluten feed, or rice bran resulted in increased soluble and insoluble fibers as well as protein content of the final diet depending on feedstuff incorporated into the standard diet. The chemical changes also resulted in, relative to the standard diet, enhanced or depressed weight gain, nutrient utilization, nutrient transporter mRNA, and profile of cecal short-chain fatty acids. Therefore, it is important to consider the gut health influence of test feedstuffs in test diets for metabolizable energy experiments. ABSTRACT: The current study was conducted to investigate the influence of short-term feeding of test diets during metabolizable energy assays on growth performance, nutrient utilization, jejunal histomorphology, cecal short-chain fatty acids, and nutrient transporters in broilers. One hundred twenty-six broiler chickens were assigned to six treatments, each with seven replicates. Experimental diets were fed between days 14 and 21. Treatments included a corn–soybean meal reference diet and five test diets with low-protein soybean meal (LPSBM), wheat bran, soy hull, corn gluten feed, or rice bran. Birds were weighed on days 14 and 21; excreta, cecal content, and jejunal tissues were collected on day 21. Seven-day weight gain was highest (p < 0.01) for birds receiving the reference diet or LPSBM, whereas FCR was lowest (p < 0.05) for birds receiving the soy hull diet. Cecal acetate and total short-chain fatty acids were higher (p < 0.05) for wheat bran compared with the soy hull test diet. Jejunal villi were longer (p < 0.05) for chickens receiving the reference diet or LPSBM test diet. Glucose transporter (GLUT1) mRNA was greater (p < 0.05) in broilers receiving rice bran compared with soy hull test diets. Therefore, when reporting energy assays, it is important that indicators of animal growth or gut health be included to help contextualize energy utilization.