Addition of Carbohydrates to Low Crude Protein Pig Diets to Reduce Manure Nitrogen Excretion and Odors

Purdue University 1998 Swine Research Report. The threat of odors emitted from pork production operations in some areas of Indiana has restricted growth of the industry and has created negative relations with residential neighbors. Odors from manure result from microbial decomposition of the organic matter and nutrients in undigested feed, and normal exogenous end products of cellular metabolism. Reducing nutrient excretions and controlling compounds creating the odors in manure are needed to significantly reduce odors emitted from pork production units. Minimizing nutrient excesses in diets, improving nutrient digestibility and utilization, and balancing nutrient levels to meet the needs of the pig and of the microflora in the digestive system are approaches needing evaluation as potential methods of odor control. Reducing the dietary crude protein level and supplementing with synthetic amino acids has reduced nitrogen excretion from pigs, with a 25 to 30% reduction reported; theoretically, a nitrogen reduction of 40 to 50% is possible. In a previous research study, total nitrogen excretion from pigs was reduced 28% by supplementing four essential synthetic amino acids (lysine, threonine, tryptophan, methionine) in a 10% crude protein corn-soy diet as compared to a standard 13% crude protein corn-soy diet. Altering the ratio of nitrogen excretion in urine and feces is a potential means for reducing ammonia emissions. By reducing the nitrogen excretion in urine as urea, which is the primary precursor for ammonia volatilization, and shifting the nitrogen excretion into the feces, which is primarily in the form of bacterial protein, ammonia volatilization is reduced. Changing the carbohydrate structure in the diet to increase bacterial utilization of nitrogen in the cecum and colon results in a significant reduction of nitrogen excretion in urine. Recent research in human and poultry nutrition suggests that the addition of small amounts of certain dietary fiber or oligosaccharides changes the bacterial populations in the lower gastrointestinal tract and reduces the amount and form of nitrogen excretion. The objectives of this study were to determine the sources and concentrations of odorous compounds in cecal contents, fresh manure and anaerobically stored manure from swine, and to determine the effects of dietary nitrogen and carbohydrate manipulation on production of odorous compounds.