Net Energy of Soybean Mill Run for Growing Cattle

The objective of the experiment was to estimate the net energies for maintenance (NEm) and gain (NEg) of soybean mill run (SMR), a by-product typically containing about 90% soyhulls. Six steers with an average weight of 288 kg were alternately fed pelleted test diets at intakes varying from 3.6 to 9.4 kg per day in an energy balance experiment arranged in a crossover design. The test diets contained either 96.6% alfalfa (ALF) or 46.6% alfalfa and 50.0% soybean mill run (ALFSMR). Energy intake from feed and losses in feces and urine were determined from total collections. Energy lost as methane and heat were determined by indirect respiration calorimetry while the steers were fed and also while fasted. Dry matter (DM), neutral detergent fiber and acid detergent fiber digestibilities were greater (P\u3c.05) for the ALF diet than the ALFSMR diet (66.7 vs 58.1%, 63.3 vs 52.5%, and 59.7 vs 45.6%, respectively). Diet protein digestibilities did not differ (P\u3e.20). Fecal energy loss was greater for the ALF diet than the ALFSMR diet (41.8 and 34.9% of gross energy intake, P\u3c.01), while urine and methane energy losses did not differ (2.6 vs 2.3% and 5.1 vs 4.8% of gross energy intake, respectively, P\u3e.20). Diet digestible and metabolizable energy estimates (Mcal/kg of DM) were 2.56 and 2.21 for ALF and 2.83 and 2.51 for ALFSMR, respectively. Partial efficiencies of ME use for maintenance (k,) and gain (kg) did not differ between diets (P\u3e.20). Using pooled k, and kg values, diet NE, and NEg estimates (Mcal/kg of DM) were 1.61 and .83 for ALF and 1.81 and .93 for ALFSMR, respectively. These data suggest that soyhulls, the major component of SMR, had NE, and NE values of 1.98 and .99 Mcal per kg of DM9, respectively