The carbon footprint from pork production can be reduced by decreasing emissions of carbon dioxide, nitrous oxide, and methane from pigs, or by reducing exretion of nitrogen from pigs. Canola meal and corn distillers dried grains with solubles (DDGS) are the two most used alternative protein sources in North America, but these ingredients have a less balanced amino acid composition than soybean meal (SBM), and they also contain more fiber. Therefore, it is possible that the use of canola meal and DDGS in pig diets increase N-excretion in manure and increase carbon dioxide and methane emissions due to increased fermentation. The current experiment aimed at testing the hypothesis that pigs fed diets based on corn and canola meal or corn and DDGS excrete more N in the manure and emit more greenhouse gases than pigs fed a corn-SBM-based diet. Twenty-four growing pigs with an initial body weight of 46.84 ± 2.25 kg were randomly allotted to three dietary treatments using a repeated 3 × 3 Latin square design with six calorimetry chambers and three consecutive periods. Four pigs (i.e., two gilts and two barrows) were housed in each chamber. Three diets were formulated with corn and one of three protein feed ingredients (i.e., SBM, canola meal, and corn DDGS). Gas analyzers measured O2 consumption and CO2 and CH4 production for determination of total heat production (THP) and fasting heat production (FHP) and for calculation of NE. Digestibility and retention of nitrogen (N) were also determined. Results indicated that weight of feces (kg/d) was lower (P < 0.05) for pigs fed the SBM diet compared with pigs fed the canola meal diet, which was lower (P < 0.05) than that of pigs fed the DDGS diet. Methan emission was not differne among diets, but pigs fed the SBM diet had greater (P < 0.05) CO2 emission than pigs fed the other diets. The NE of the SBM diet was not different from that of pigs fed the other diets, but the NE of the canola meal diet was less (P < 0.05) than that of the DDGS diet. However, nitrogen excretion in feces (g/d) was reduced (P < 0.05), and nitrogen absorption (g/d) was greater (P < 0.05) for pigs fed the SBM diet compared to those fed the DDGS diet. Nitrogen absorption (g/d) was greater (P < 0.05) for the SBM diet compared with the other diets. In conclusion, feeding diets based on SBM will reduce the N-excretion from pigs and thereby lower the environmental effects of swine production.

Results of this experiment demonstrated that diets based on corn and SBM will result in reduced excretion of Nitrogen in the manure. Therefore, results of this research will contribute to convincing swine producers and integrators that the environmental footprint of SBM-based diets is less than of diets containing other protein sources. This will result in increased demand for SBM, which ultimately will result in increased profit to soybean producers.