Greenhouse gas production and performance of growing pigs fed high wheat millrun diets supplemented with a multi-carbohydrase enzyme

Abstract

The inclusion of wheat millrun, a low-cost milling co-product, into swine rations is limited by high non-starch polysaccharide (NSP) content. The high NSP content may decrease digestibility and performance and increase fermentation, perhaps leading to increased greenhouse gas (GHG) production. The high NSP content also suggests that carbohydrase enzymes may improve digestibility. This thesis, therefore, evaluated the impact of wheat millrun and enzyme (carbohydrase) supplementation in diets of growing-finishing pigs on the environment (GHG production) and performance of pigs. A partial life cycle analysis (LCA) was performed to assess GHG output when feed production and manure management was considered. A performance study carried out in the first experiment, showed no interactive effects on growth performance and nutrient digestibility when wheat millrun was supplemented with multi-carbohydrase enzymes in diets of growing-finishing pigs. Increasing wheat millrun linearly reduced energy, nitrogen (N) and phosphorus (P) apparent total-tract digestibility (ATTD) and net energy (NE) content whiles enzyme reduced energy digestibility but not N or P ATTD. Overall average daily gain (ADG) and gain to feed ratio (G:F) were reduced, and average daily feed intake (ADFI) was unaffected in pigs fed the wheat millrun diets. Pigs on the enzyme supplemented diets experienced reduced G:F in the first 14 d. Neither wheat millrun nor multi-carbohydrase supplementation affected days to market. In the second experiment, wheat millrun inclusion in swine diets failed to increase GHG (CO2, N2O, CH4) emissions from growing pigs housed in environmental chambers. Multi-carbohydrase supplementation also had no effect on GHG production. There was an increase in CO2 flux and a decrease in CH4 flux in manure gas measurements with time. In the final experiment, data from the Holos model used in an LCA framework indicated that when feed production was considered, feeding pigs up to 30 % wheat millrun inclusion in the diet could result in about a 25 % reduction in GHG emission in terms of global warming potential (GWP). In summary, the results indicate that feeding growing-finishing pigs up to 30 % wheat millrun diets may be beneficial to the farmer and the environment as it reduces GHG emissions when feed production is also considered.