Three experiments were conducted to determine the effects of DDGS on nutrient excretion and gaseous emissions by swine. In Exp. 1, a total of 80 pigs initially weighing 36.8 kg were blocked by weight and allotted to four dietary treatments. Dietary treatments were randomly allotted to four rooms with 2 pens per room (20 pigs/room). Each room was housed within the same building with each room receiving the same incoming air. Each room was equipped with a shallow pit, pull-plug manure system. Thus, each room served as the experimental unit. All pigs within a room were fed one of four diets.
The four dietary treatments included a fortified corn-soybean meal diet (control) or a corn-soybean meal diet with the addition of 10, 20, or 40% distillers dried grains with solubles (DDGS). The corn DDGS was purchased from a new generation ethanol plant. The DDGS diets were formulated to a similar standardized ileal digestible (SID) Lys content and digestible P content as the control diet. Thus, all diets contained similar levels of DM, SID Lys, and digestible P. However, CP and S concentrations increased with increasing DDGS levels. Also, macro- and micro-mineral concentrations varied among diets due to the contribution from DDGS.
Each week, the pigs were removed from each room and weighed. At this time, the feeders were weighed to calculate feed intake and a feed sample was collected from each feeder. Nutrient concentration of the slurry was multiplied by total pit volume to achieve total nutrient output by phase. Airflow from each fan was continuously measured and ammonia and hydrogen sulfide concentrations in the exhaust air were measured. The generation and emission rates of each gas were calculated. The emission rates for each room were based on the mean gas concentration in the exhaust air of each room and the total airflow rate for each sampling cycle.
Daily gain tended to decrease with increasing DDGS. Increasing DDGS did not affect ADFI. However, G:F ratio decreased with increasing DDGS. The daily intake of DM was similar among dietary treatments. However, N and S intakes increased with increasing DDGS. The intake of P tended to decrease with increasing DDGS.
Slurry volume tended to increase for pigs fed increasing DDGS. Pigs fed 40% DDGS had a 15% greater slurry volume compared with pigs fed 0% DDGS. However, slurry pH was reduced for pigs fed increasing DDGS. Nutrient concentration of the slurry was multiplied by total volume of the slurry and divided by the number of pigs and days on test to calculate excretion on a g/pig/d basis. The excretion of DM, N, Mg, Na, and S were increased markedly for pigs fed increasing DDGS. The excretion of P, Ca, Cu, and Zn also tended to be increased for pigs fed DDGS.
Airflow was similar for all rooms. Increasing DDGS increased the concentration of NH3, H2S, CO2, CH4, and N2O in the exhaust air. The emission rates (mg/min) of these gases were also increased with increasing DDGS. When calculated on a per pig basis, the emissions of these gases were increased for pigs fed increasing DDGS.
In Exp. 2, pigs were fed either a control diet or the control diet with 25% DDGS for the entire finishing period. The DDGS diet was formulated to a similar SID Lys content and digestible P content as the control diet. Crystalline Lys, Thr, and Trp were added as needed to the DDGS diet in order to equalize CP similar to that in the control diet. Digestible P was allowed to decrease with age in the control diet, but it remained higher in the DDGS diet due to the contribution from DDGS. In addition, phytase was added to each diet. Thus, both diets contained similar levels of DM, CP, and SID Lys. Digestible P and S content were greater in the DDGS diet. Also, macro- and micro-mineral concentration varied between diets due to the contribution from DDGS.
The addition of 25% DDSG tended to slightly reduce ADG resulting in a slight reduction in final weight. Addition of 25% DDGS did not affect feed intake or G:F ratio. The daily intakes of DM and N were similar for both dietary treatments. However, S intake increased with the addition of DDGS. The intake of P tended to increase with DDGS.
Slurry volume was increased by 16% for pigs fed DDGS; however, this difference was not significant. Slurry pH was reduced for pigs fed 25% DDGS. The excretion of DM, Na, and S were increased markedly for pigs fed 25% DDGS. Cumulative excretion of DM and S per pig for the entire finishing period was increased for pigs fed DDGS.
Airflow was similar for all rooms. Unlike Exp. 1, the concentration and emission of NH3 was similar for pigs fed both diets most likely due to the equalization of protein content in the diets. However, H2S concentration and emission rate was increased for pigs fed DDGS. Also, the emission of CH4 per pig was increased with DDGS. The concentration and emissions of CO2 and N2O were not affected by diet.
In Exp. 3, two similar gestation barns, each housing 44 sows, were used to determine the effect of DDGS inclusion in gestation diets on nutrient excretion. Sow parity and gestation stage (early, mid, late gestation) were equalized between barns. Two dietary treatments consisting of a fortified corn-soybean meal diet and an experimental diet with 40% DDGS inclusion in a corn-soybean meal diet were compared during a 2-phase crossover design. Each period consisted of a 2-week adaptation period, followed by a 4-week collection period. Following the 2-week adjustment where sows were fed their respective dietary treatment, a 4-week collection period began. Following this 1st period, dietary treatments were switched between barns and the 2nd six-week period commenced. The daily intakes of DM and P were similar; however, N and S intakes increased for sows fed DDGS. Pit characteristics, pH, and temperature were similar for sows fed both diets. However, volume was increased by 12% for sows fed DDGS. The daily excretion of DM, Mg, and S were increased for sows fed DDGS. The excretion of N was numerically increased for sows fed DDGS. However, little effect was observed for the other nutrients. The concentrations of NH3, H2S, CH4, and N2O in exhaust air were increased for sows fed DDGS.
In summary, these results suggest that feeding high levels of DDGS to finishing pigs and gestating sows may increase environmental issues for swine facilities. Increasing DDGS in the diet increased DM and S excretion dramatically, while N excretion can be limited. These tremendous increases in excretion resulted in significant increases in CH4 and H2S emissions for swine fed DDGS. Ammonia and N2O emissions can be controlled by minimizing the increase in dietary CP when feeding DDGS. Methods to enhance DM digestibility and reduce S content of DDGS must be explored to limit the environmental implications when feeding high levels of DDGS. This project was funded by the National Pork Checkoff.
Scott D. Carter, Ph.D.
212B Animal Science
Oklahoma State University
Stillwater, OK 74078